[vlc-devel] [PATCH v4] linux: kernel mode setting (KMS) vout plugin

Steve Lhomme robux4 at ycbcr.xyz
Tue Jun 26 10:06:22 CEST 2018


On 6/11/2018 2:34 PM, Juha-Pekka Heikkila wrote:
> Add new kernel mode setting video output plugin.
> By default it tries to match vlc suggested video mode to anything
> kms api offers. There are command line parameters to control
> which video format to use for both vlc and for drm.
>
> kms-vlc-chroma parameter to force VLC to use FourCC as output.
> kms-drm-chroma parameter to overide DRM requested framebuffer type.
>
> v4: rebase
>
> v3: Increased HW frame amount to 3 to be able to reduce stall
> from kernel. HW frame amount can be now changed by changing
> defined MAXHWBUF. General cleanup.
> Rémi Denis-Courmont: I kept module description in beginning
> of kms.c, otherwise my plugin look different from all other
> plugins in this. I changed desciption for my commandline

Not all plugins. We now try to avoid this. It's even easier to find a 
module definition by scrolling down at the bottom of the file.

> parameters in hope to underline their different function.
> Destruction of HW buffers is now moved to picture destroy
> callback.
>
> v2, Rémi Denis-Courmont: Multiple picture pools are gone as well as
> TTY code which I found out I don't need.
> vlc_fourcc_GetYUVFallback/vlc_fourcc_GetRGBFallback I didn't find
> easy way to do back'n'forth mapping of what kernel offers and what
> vlc offers thus I have simple table of most common formats which
> my plugin uses to find 'best' match.
>
> Signed-off-by: Juha-Pekka Heikkila <juhapekka.heikkila at gmail.com>
> ---
>   configure.ac                     |   5 +
>   modules/video_output/Makefile.am |  10 +
>   modules/video_output/kms.c       | 829 +++++++++++++++++++++++++++++++++++++++
>   3 files changed, 844 insertions(+)
>   create mode 100644 modules/video_output/kms.c
>
> diff --git a/configure.ac b/configure.ac
> index dfb8ecd..564c32b 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -3392,6 +3392,11 @@ AC_CHECK_HEADER([linux/fb.h], [
>   ])
>   
>   dnl
> +dnl  Linux kernel mode setting module
> +dnl
> +PKG_ENABLE_MODULES_VLC([KMS], [], [libdrm >= 2.4.83], [Linux kernel mode setting output], [auto])
> +
> +dnl
>   dnl  libcaca plugin
>   dnl
>   PKG_ENABLE_MODULES_VLC([CACA], [], [caca >= 0.99.beta14], [libcaca output],[auto])
> diff --git a/modules/video_output/Makefile.am b/modules/video_output/Makefile.am
> index 5d18a36..2be8758 100644
> --- a/modules/video_output/Makefile.am
> +++ b/modules/video_output/Makefile.am
> @@ -422,6 +422,16 @@ EXTRA_LTLIBRARIES += libfb_plugin.la
>   vout_LTLIBRARIES += $(LTLIBfb)
>   
>   
> +### Kernel Mode Setting ###
> +
> +libkms_plugin_la_SOURCES = video_output/kms.c
> +libkms_plugin_la_CFLAGS = $(AM_CFLAGS) $(KMS_CFLAGS)
> +libkms_plugin_la_LIBADD = $(KMS_LIBS)
> +libkms_plugin_la_LDFLAGS = $(AM_LDFLAGS) -rpath '$(voutdir)'
> +EXTRA_LTLIBRARIES += libkms_plugin.la
> +vout_LTLIBRARIES += $(LTLIBkms)
> +
> +
>   ### Coloured ASCII art ###
>   libcaca_plugin_la_SOURCES = video_output/caca.c
>   libcaca_plugin_la_CFLAGS = $(AM_CFLAGS) $(CACA_CFLAGS)
> diff --git a/modules/video_output/kms.c b/modules/video_output/kms.c
> new file mode 100644
> index 0000000..e26c38b
> --- /dev/null
> +++ b/modules/video_output/kms.c
> @@ -0,0 +1,829 @@
> +/*****************************************************************************
> + * kms.c : kernel mode setting plugin for vlc
> + *****************************************************************************
> + * Copyright © 2018 Intel Corporation
> + *
> + * Permission is hereby granted, free of charge, to any person obtaining a
> + * copy of this software and associated documentation files (the "Software"),
> + * to deal in the Software without restriction, including without limitation
> + * the rights to use, copy, modify, merge, publish, distribute, sublicense,
> + * and/or sell copies of the Software, and to permit persons to whom the
> + * Software is furnished to do so, subject to the following conditions:
> + *
> + * The above copyright notice and this permission notice (including the next
> + * paragraph) shall be included in all copies or substantial portions of the
> + * Software.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
> + * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
> + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
> + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
> + * IN THE SOFTWARE.
> + *****************************************************************************/
> +
> +/*****************************************************************************
> + * Preamble
> + *****************************************************************************/
> +
> +#ifdef HAVE_CONFIG_H
> +# include "config.h"
> +#endif
> +
> +#include <fcntl.h>
> +#include <sys/mman.h>
> +
> +#include <xf86drm.h>
> +#include <xf86drmMode.h>
> +#include <drm_fourcc.h>
> +
> +#include <vlc_common.h>
> +#include <vlc_plugin.h>
> +#include <vlc_vout_display.h>
> +#include <vlc_picture_pool.h>
> +#include <vlc_fs.h>
> +
> +/*****************************************************************************
> + * Module descriptor
> + *****************************************************************************/
> +#define KMS_VAR "kms"
> +
> +#define DEVICE_TEXT N_("Framebuffer device")
> +#define DEVICE_LONGTEXT N_(\
> +    "Framebuffer device to use for rendering (usually /dev/dri/card0).")
> +
> +#define VLC_CHROMA_TEXT N_("Image format used by VLC")
> +#define VLC_CHROMA_LONGTEXT N_("Chroma fourcc request to VLC for output format")
> +
> +#define DRM_CHROMA_TEXT N_("Image format used by DRM")
> +#define DRM_CHROMA_LONGTEXT N_("Chroma fourcc override for DRM framebuffer format selection")
> +
> +static int  Open (vlc_object_t *);
> +static void Close(vlc_object_t *);
> +
> +vlc_module_begin ()
> +    set_shortname("kms")
> +    set_category(CAT_VIDEO)
> +    set_subcategory(SUBCAT_VIDEO_VOUT)
> +    add_loadfile(KMS_VAR, "/dev/dri/card0", DEVICE_TEXT, DEVICE_LONGTEXT)
> +
> +    add_string( "kms-vlc-chroma", NULL, VLC_CHROMA_TEXT, VLC_CHROMA_LONGTEXT,
> +                true)
> +    add_string( "kms-drm-chroma", NULL, DRM_CHROMA_TEXT, DRM_CHROMA_LONGTEXT,
> +                true)
> +    set_description(N_("Linux kernel mode setting video output"))
> +    set_capability("vout display", 30)
> +    set_callbacks(Open, Close)
> +vlc_module_end ()
> +
> +/*****************************************************************************
> + * Local prototypes
> + *****************************************************************************/
> +
> +/*
> + * how many hw buffers are allocated for page flipping. I think
> + * 3 is enough so we shouldn't get unexpected stall from kernel.
> + */
> +#define   MAXHWBUF 3
> +
> +typedef enum { drvSuccess, drvTryNext, drvFail } deviceRval;
> +
> +struct vout_display_sys_t {
> +/*
> + * buffer information
> + */
> +    uint32_t        width;
> +    uint32_t        height;
> +    uint32_t        stride;
> +    uint32_t        size;
> +    uint32_t        offsets[PICTURE_PLANE_MAX];
> +
> +    uint32_t        handle[MAXHWBUF];
> +    uint8_t         *map[MAXHWBUF];
> +
> +    uint32_t        fb[MAXHWBUF];
> +    picture_t       *picture;
> +    picture_pool_t  *pool;
> +
> +    unsigned int    front_buf;
> +
> +    bool            forced_drm_fourcc;
> +    uint32_t        drm_fourcc;
> +    vlc_fourcc_t    vlc_fourcc;
> +
> +/*
> + * modeset information
> + */
> +    uint32_t        crtc;
> +    uint32_t        plane_id;
> +
> +/*
> + * other generic stuff
> + */
> +    int             drm_fd;
> +};
> +
> +typedef struct {
> +    vout_display_sys_t  *p_voutsys;
> +} picture_sys_t;
> +
> +
> +static void DestroyFB(vout_display_sys_t const *sys, uint32_t const buf)
> +{
> +    struct drm_mode_destroy_dumb destroy_req = { .handle = sys->handle[buf] };
> +
> +    munmap(sys->map[buf], sys->size);
> +    drmModeRmFB(sys->drm_fd, sys->fb[buf]);
> +    drmIoctl(sys->drm_fd, DRM_IOCTL_MODE_DESTROY_DUMB, &destroy_req);
> +}
> +
> +
> +#define ALIGN(v, a) (((v) + (a)-1) & ~((a)-1))
> +
> +static deviceRval CreateFB(vout_display_t *vd, const int buf)
> +{
> +    vout_display_sys_t *sys = vd->sys;
> +    struct drm_mode_create_dumb create_req = { .width = sys->width*2,
> +                                               .height = sys->height,
> +                                               .bpp = 16 };
> +    struct drm_mode_destroy_dumb destroy_req;
> +    struct drm_mode_map_dumb modify_req = {};
> +    unsigned int tile_width = 512, tile_height = 16;
> +    deviceRval ret;
> +    int i;
> +    uint32_t offsets[] = {0,0,0,0}, handles[] = {0,0,0,0},
> +            pitches[] = {0,0,0,0};
> +
> +    switch(sys->drm_fourcc) {
> +#ifdef DRM_FORMAT_P010
> +    case DRM_FORMAT_P010:
> +#endif
> +#ifdef DRM_FORMAT_P012
> +    case DRM_FORMAT_P012:
> +#endif
> +#ifdef DRM_FORMAT_P016
> +    case DRM_FORMAT_P016:
> +#endif
> +#if defined(DRM_FORMAT_P010) || defined(DRM_FORMAT_P012) || defined(DRM_FORMAT_P016)
> +        sys->stride = ALIGN(sys->width*2, tile_width);
> +        sys->offsets[1] = sys->stride*ALIGN(sys->height, tile_height);
> +        create_req.height = ALIGN(sys->height*2, tile_height);

Shouldn't it be 2*ALIGN(sys->height, tile_height)? You may have 
misaligned buffers if the alignment doesn't add the same value.
> +        break;
> +#endif
> +    case DRM_FORMAT_NV12:
> +        sys->stride = ALIGN(sys->width, tile_width);
> +        sys->offsets[1] = sys->stride*ALIGN(sys->height, tile_height);
> +        create_req.height = ALIGN(sys->height*2, tile_height);
> +        break;
> +    default:
> +        create_req.height = ALIGN(sys->height*2, tile_height);
> +
> +        /*
> +         * width *4 so there's enough space for anything.
> +         */
> +        sys->stride = ALIGN(sys->width*4, tile_width);

So 4*ALIGN(sys->width, tile_width)?
> +        break;
> +    }
> +
> +    ret = drmIoctl(sys->drm_fd, DRM_IOCTL_MODE_CREATE_DUMB, &create_req);
> +    if (ret < 0) {
> +        msg_Err(vd, "Cannot create dumb buffer");
> +        return drvFail;
> +    }
> +
> +    sys->size = create_req.size;
> +    sys->handle[buf] = create_req.handle;
> +
> +    /*
> +     * create framebuffer object for the dumb-buffer
> +     * index 0 has to be filled in any case.
> +     */
> +    for (i = 0; i < 4 && (sys->offsets[i] || i < 1); i++) {
> +        handles[i] = create_req.handle;

instead of 4 use ARRAY_SIZE(handles)



> +        pitches[i] = sys->stride;
> +        offsets[i] = sys->offsets[i];
> +    }
> +
> +    ret = drmModeAddFB2(sys->drm_fd, sys->width, sys->height, sys->drm_fourcc,
> +                        handles, pitches, offsets, &sys->fb[buf], 1<<1);

If 1<<1 is a flag maybe it has a pretty name ?

> +
> +    if (ret) {
> +        msg_Err(vd, "Cannot create frame buffer");
> +        ret = drvFail;
> +        goto err_destroy;
> +    }
> +
> +    modify_req.handle = sys->handle[buf];
> +    ret = drmIoctl(sys->drm_fd, DRM_IOCTL_MODE_MAP_DUMB, &modify_req);
> +    if (ret) {
> +        msg_Err(vd, "Cannot map dumb buffer");
> +        ret = drvFail;
> +        goto err_fb;
> +    }
> +
> +    sys->map[buf] = mmap(0, sys->size, PROT_READ | PROT_WRITE, MAP_SHARED,
> +                         sys->drm_fd, modify_req.offset);
> +
> +    if (sys->map[buf] == MAP_FAILED) {
> +        msg_Err(vd, "Cannot mmap dumb buffer");
> +        ret = drvFail;
> +        goto err_fb;
> +    }
> +    return drvSuccess;
> +
> +err_fb:
> +    drmModeRmFB(sys->drm_fd, sys->fb[buf]);
> +    sys->fb[buf] = 0;
> +
> +err_destroy:
> +    memset(&destroy_req, 0, sizeof(destroy_req));
> +    destroy_req.handle = sys->handle[buf];
> +    drmIoctl(sys->drm_fd, DRM_IOCTL_MODE_DESTROY_DUMB, &destroy_req);
> +    return ret;
> +}
> +
> +
> +static deviceRval FindCRTC(vout_display_t *vd, drmModeRes const *res,
> +                             drmModeConnector const *conn)
> +{
> +    vout_display_sys_t *sys = vd->sys;
> +    drmModeEncoder *enc;
> +    int i, j;
> +
> +    /*
> +     * Try current encoder and CRTC combo
> +     */
> +    if (conn->encoder_id) {
> +        enc = drmModeGetEncoder(sys->drm_fd, conn->encoder_id);
> +        if (enc) {
> +            if (enc->crtc_id) {
> +                msg_Dbg(vd, "Got CRTC %d from current encoder", enc->crtc_id);
> +
> +                sys->crtc = enc->crtc_id;
> +                drmModeFreeEncoder(enc);
> +                return drvSuccess;
> +            }
> +            drmModeFreeEncoder(enc);
> +        }
> +    }
> +
> +    /*
> +     * Iterate all available encoders to find CRTC
> +     */
> +    for (i = 0; i < conn->count_encoders; i++) {
> +        enc = drmModeGetEncoder(sys->drm_fd, conn->encoders[i]);
> +
> +        for (j = 0; enc && j < res->count_crtcs; ++j) {
> +            if (ffs(enc->possible_crtcs) == j && res->crtcs[j]) {
> +                msg_Dbg(vd, "Got CRTC %d", res->crtcs[j]);
> +                sys->crtc = res->crtcs[j];
> +                drmModeFreeEncoder(enc);
> +                return drvSuccess;
> +            }
> +        }
> +        drmModeFreeEncoder(enc);
> +    }
> +
> +    msg_Err(vd , "Cannot find CRTC for connector %d", conn->connector_id);
> +    return drvTryNext;
> +}
> +
> +
> +static deviceRval SetupDevice(vout_display_t *vd, drmModeRes const *res,
> +                             drmModeConnector const *conn)
> +{
> +    vout_display_sys_t *sys = vd->sys;
> +    deviceRval ret;
> +    int c, c2;
> +
> +    if (conn->connection != DRM_MODE_CONNECTED || conn->count_modes == 0)
> +        return drvTryNext;
> +
> +    sys->width = conn->modes[0].hdisplay;
> +    sys->height = conn->modes[0].vdisplay;
> +    msg_Dbg(vd, "Mode resolution for connector %u is %ux%u",
> +            conn->connector_id, sys->width, sys->height);
> +
> +    ret = FindCRTC(vd, res, conn);
> +    if (ret != drvSuccess) {
> +        msg_Dbg(vd , "No valid CRTC for connector %d", conn->connector_id);
> +        return ret;
> +    }
> +
> +    for (c = 0; c < MAXHWBUF; c++) {
> +        ret = CreateFB(vd, c);
> +        if (ret != drvSuccess) {
> +            msg_Err(vd, "Cannot create framebuffer %d for connector %d", c,
> +                    conn->connector_id);
> +            for (c2 = 0; c2 < c; c2++)
> +                DestroyFB(sys, c2);
> +
> +            return ret;
> +        } else {
> +            msg_Dbg(vd, "Created HW framebuffer %d/%d", c+1, MAXHWBUF);
> +        }
> +    }
> +    return drvSuccess;
> +}
> +
> +
> +/** fourccmatching, matching drm to vlc fourccs and see if it was present
> + * in HW. Here really is two lists, one in RGB and second in YUV. They're
> + * listed in order of preference.
> + *
> + * fourccmatching::drm DRM fourcc code from drm_fourcc.h
> + * fourccmatching::vlc VLC fourcc code from vlc_fourcc.h under title 'Chromas'
> + * fourccmatching::plane_id from which plane this DRM fourcc was found
> + * fourccmatching::present if this mode was available in HW
> + * fourccmatching::isYUV as name suggest..
> + */
> +static struct
> +{
> +    uint32_t     drm;
> +    vlc_fourcc_t vlc;
> +    uint32_t     plane_id;
> +    bool         present;
> +    bool         isYUV;
> +} fourccmatching[] = {
> +    { .drm = DRM_FORMAT_XRGB8888, .vlc = VLC_CODEC_RGB32, .isYUV = false },
> +    { .drm = DRM_FORMAT_RGB565, .vlc = VLC_CODEC_RGB16, .isYUV = false },
> +#if defined DRM_FORMAT_P010
> +    { .drm = DRM_FORMAT_P010, .vlc = VLC_CODEC_P010, .isYUV = true },
> +#endif
> +    { .drm = DRM_FORMAT_NV12, .vlc = VLC_CODEC_NV12, .isYUV = true },
> +    { .drm = DRM_FORMAT_YUYV, .vlc = VLC_CODEC_YUYV, .isYUV = true },
> +    { .drm = DRM_FORMAT_YVYU, .vlc = VLC_CODEC_YVYU, .isYUV = true },
> +    { .drm = DRM_FORMAT_UYVY, .vlc = VLC_CODEC_UYVY, .isYUV = true },
> +    { .drm = DRM_FORMAT_VYUY, .vlc = VLC_CODEC_VYUY, .isYUV = true },
> +};
> +
> +
> +static void CheckFourCCList(uint32_t drmfourcc, uint32_t plane_id)
> +{
> +    unsigned i;
> +
> +    for (i = 0; i < ARRAY_SIZE(fourccmatching); i++) {
> +        if (fourccmatching[i].drm == drmfourcc) {
> +            if (fourccmatching[i].present)
> +                /* this drmfourcc already has a plane_id found where it
> +                 * could be used, we'll stay with earlier findings.
> +                 */
> +                break;
> +
> +            fourccmatching[i].present = true;
> +            fourccmatching[i].plane_id = plane_id;
> +            break;
> +        }
> +    }
> +}
> +
> +
> +static bool ChromaNegotiation(vout_display_t *vd)
> +{
> +    vout_display_sys_t *sys = vd->sys;
> +    unsigned i, c, propi;
> +    uint32_t planetype;
> +    const char types[][16] = { "OVERLAY", "PRIMARY", "CURSOR", "UNKNOWN" };
> +    drmModePlaneRes *plane_res = NULL;
> +    drmModePlane *plane;
> +    drmModeObjectProperties *props;
> +    drmModePropertyPtr pp;
> +    bool YUVFormat;
> +
> +    /*
> +     * For convenience print out in debug prints all supported
> +     * DRM modes so they can be seen if use verbose mode.
> +     */
> +    plane_res = drmModeGetPlaneResources(sys->drm_fd);
> +    sys->plane_id = 0;
> +
> +    if (plane_res != NULL && plane_res->count_planes > 0) {
> +        msg_Dbg(vd, "List of DRM supported modes on this machine:");
> +        for (c = 0; c < plane_res->count_planes; c++) {
> +
> +            plane = drmModeGetPlane(sys->drm_fd, plane_res->planes[c]);
> +            if (plane != NULL && plane->count_formats > 0) {
> +                props = drmModeObjectGetProperties(sys->drm_fd,
> +                                                   plane->plane_id,
> +                                                   DRM_MODE_OBJECT_PLANE);
> +
> +                planetype = 3;
> +                pp = NULL;
> +                for (propi = 0; propi < props->count_props; propi++) {
> +                    pp = drmModeGetProperty(sys->drm_fd, props->props[propi]);
> +                    if (strcmp(pp->name, "type") == 0) {
> +                        break;
> +                    }
> +                    drmModeFreeProperty(pp);
> +                }
> +
> +                if (pp != NULL) {
> +                    drmModeFreeProperty(pp);
> +                    planetype = props->prop_values[propi];
> +                }
> +
> +                for (i = 0; i < plane->count_formats; i++) {
> +                    CheckFourCCList(plane->formats[i], plane->plane_id);
> +
> +                    if (sys->forced_drm_fourcc && sys->plane_id == 0 &&
> +                            plane->formats[i] == sys->drm_fourcc) {
> +                        sys->plane_id = plane->plane_id;
> +                    }
> +
> +                    /*
> +                     * we don't advertise about cursor plane because
> +                     * of its special limitations.
> +                     */
> +                    if (planetype != DRM_PLANE_TYPE_CURSOR) {
> +                        msg_Dbg(vd, "plane id %d type %s pipe %c format %2d: %.4s",
> +                                plane->plane_id, types[planetype],
> +                                ('@'+ffs(plane->possible_crtcs)), i,
> +                                (char*)&plane->formats[i]);
> +                    }
> +                }
> +                drmModeFreePlane(plane);
> +            } else {
> +                msg_Err(vd, "Couldn't get list of DRM formats");
> +                drmModeFreePlaneResources(plane_res);
> +                return false;
> +            }
> +        }
> +        drmModeFreePlaneResources(plane_res);
> +    }
> +
> +    if (sys->forced_drm_fourcc) {
> +        for (c = i = 0; c < ARRAY_SIZE(fourccmatching); c++) {
> +            if (fourccmatching[c].drm == sys->drm_fourcc) {
> +                sys->vlc_fourcc = fourccmatching[c].vlc;
> +                break;
> +            }
> +        }
> +        if (sys->plane_id == 0) {
> +            msg_Err(vd, "Forced DRM fourcc (%.4s) not available in kernel.",
> +                    (char*)&sys->drm_fourcc);
> +            return false;
> +        }
> +        return true;
> +    }
> +
> +    /*
> +     * favor yuv format according to YUVFormat flag.
> +     * check for exact match first, then YUVFormat and then !YUVFormat
> +     */
> +    YUVFormat = vlc_fourcc_IsYUV(sys->vlc_fourcc);

You may read this value right before you need it. In this first loop 
it's not used.
> +    for (c = i = 0; c < ARRAY_SIZE(fourccmatching); c++) {
> +        if (fourccmatching[c].vlc == sys->vlc_fourcc) {
> +            if (!sys->forced_drm_fourcc && fourccmatching[c].present) {
> +                sys->drm_fourcc = fourccmatching[c].drm;
> +                sys->plane_id = fourccmatching[c].plane_id;
> +             }
> +
> +            if (!sys->drm_fourcc) {
> +                msg_Err(vd, "Forced VLC fourcc (%.4s) not matching anything available in kernel, please set manually",
> +                        (char*)&sys->vlc_fourcc);
> +                return false;
> +            }
> +            return true;
> +        }
> +    }
> +
> +    for (c = i = 0; c < ARRAY_SIZE(fourccmatching); c++) {
> +        if (fourccmatching[c].isYUV == YUVFormat
> +                && fourccmatching[c].present) {
> +            if (!sys->forced_drm_fourcc) {
> +                sys->drm_fourcc = fourccmatching[c].drm;
> +                sys->plane_id = fourccmatching[c].plane_id;
> +             }
> +
> +            sys->vlc_fourcc = fourccmatching[c].vlc;
> +            return true;
> +        }
> +    }
> +
> +    for (i = 0; c < ARRAY_SIZE(fourccmatching); c++) {
> +        if (!fourccmatching[c].isYUV != YUVFormat
> +                && fourccmatching[c].present) {
> +            if (!sys->forced_drm_fourcc) {
> +                sys->drm_fourcc = fourccmatching[c].drm;
> +                sys->plane_id = fourccmatching[c].plane_id;
> +             }
> +
> +            sys->vlc_fourcc = fourccmatching[c].vlc;
> +            return true;
> +        }
> +    }
> +
> +    return false;
> +}
> +
> +
> +static int OpenDisplay(vout_display_t *vd)
> +{
> +    vout_display_sys_t *sys = vd->sys;
> +    char *psz_device;
> +    int ret;
> +    uint64_t dumbRet;
> +    drmModeConnector *conn;
> +    drmModeRes *modeRes;
> +    int c;
> +    bool found_connector = false;
> +
> +    /*
> +     * Open framebuffer device
> +     */
> +    psz_device = var_InheritString(vd, KMS_VAR);
> +    if (psz_device == NULL) {
> +        msg_Err(vd, "Don't know which DRM device to open");
> +        return VLC_EGENERIC;
> +    }
> +
> +    sys->drm_fd = vlc_open(psz_device, O_RDWR);
> +    if (sys->drm_fd == -1) {
> +        msg_Err(vd, "cannot open %s", psz_device);
> +        free(psz_device);
> +        return VLC_EGENERIC;
> +    }
> +
> +    ret = drmSetMaster(sys->drm_fd);
> +    if (ret < 0) {
> +        msg_Err(vd, "Cannot become DRM master on %s", psz_device);
> +
> +        free(psz_device);
> +        vlc_close(sys->drm_fd);
> +        sys->drm_fd = 0;
> +        return VLC_EGENERIC;
> +    }
> +    free(psz_device);
> +
> +    drmSetClientCap(sys->drm_fd, DRM_CLIENT_CAP_UNIVERSAL_PLANES, 1);
> +
> +    if (!ChromaNegotiation(vd)) {

No error message here ?
Maybe use a goto as the code is similar to the following error handling.

> +        drmDropMaster(sys->drm_fd);
> +        vlc_close(sys->drm_fd);
> +        sys->drm_fd = 0;
> +        return VLC_EGENERIC;
> +    }
> +
> +    msg_Dbg(vd, "Using VLC chroma '%.4s', DRM chroma '%.4s'",
> +            (char*)&sys->vlc_fourcc, (char*)&sys->drm_fourcc);
> +
> +    ret = drmGetCap(sys->drm_fd, DRM_CAP_DUMB_BUFFER, &dumbRet);
> +    if (ret < 0 || !dumbRet) {
> +        msg_Err(vd, "Device '%s' does not support dumb buffers", psz_device);
> +        drmDropMaster(sys->drm_fd);
> +        vlc_close(sys->drm_fd);
> +        sys->drm_fd = 0;
> +        return VLC_EGENERIC;
> +    }
> +
> +    modeRes = drmModeGetResources(sys->drm_fd);
> +    if (modeRes == NULL) {
> +        msg_Err(vd, "Didn't get DRM resources");
> +        vlc_close(sys->drm_fd);
> +        drmDropMaster(sys->drm_fd);
> +        sys->drm_fd = 0;
> +        return VLC_EGENERIC;
> +    }
> +
> +    for (c = 0; c < modeRes->count_connectors && sys->crtc == 0; c++) {
> +
> +        conn = drmModeGetConnector(sys->drm_fd, modeRes->connectors[c]);
> +        if (conn == NULL)
> +            continue;
> +
> +        found_connector = true;
> +
> +        ret = SetupDevice(vd, modeRes, conn);
> +        if (ret != drvSuccess) {
> +            if (ret != drvTryNext) {
> +                msg_Err(vd, "Cannot do setup for connector %u:%u", c,
> +                        modeRes->connectors[c]);
> +
> +                drmModeFreeConnector(conn);
> +                drmModeFreeResources(modeRes);
> +                drmDropMaster(sys->drm_fd);
> +                vlc_close(sys->drm_fd);
> +                sys->drm_fd = 0;
> +                return VLC_EGENERIC;
> +            }
> +            drmModeFreeConnector(conn);
> +            found_connector = false;
> +            continue;
> +        }
> +        drmModeFreeConnector(conn);
> +    }
> +    drmModeFreeResources(modeRes);
> +    if (!found_connector) {
> +        drmModeFreeResources(modeRes);
> +        drmDropMaster(sys->drm_fd);
> +        vlc_close(sys->drm_fd);
> +        sys->drm_fd = 0;
> +        return VLC_EGENERIC;
> +    }
> +    return VLC_SUCCESS;
> +}
> +
> +
> +static int Control(vout_display_t *vd, int query, va_list args)
> +{
> +    VLC_UNUSED(vd);
> +    VLC_UNUSED(query);
> +    VLC_UNUSED(args);
> +    return VLC_EGENERIC;
> +}
> +
> +
> +static void CustomDestroyPicture(picture_t *p_picture)
> +{
> +    picture_sys_t *psys = (picture_sys_t*)p_picture->p_sys;
> +    vout_display_sys_t *sys = (vout_display_sys_t *)psys->p_voutsys;
> +    int c;
> +
> +    for (c = 0; c < MAXHWBUF; c++)
> +        DestroyFB(sys, c);

Given the buffers/resources are not allocated when the pool is created, 
they should not be released when the pool is released. In this case when 
the module is released.

> +
> +    drmSetClientCap(sys->drm_fd, DRM_CLIENT_CAP_UNIVERSAL_PLANES, 0);
> +    drmDropMaster(sys->drm_fd);
> +    vlc_close(sys->drm_fd);
> +    sys->drm_fd = 0;
> +    free(p_picture->p_sys);
> +    free(p_picture);
> +}
> +
> +
> +static picture_pool_t *Pool(vout_display_t *vd, unsigned count)
> +{
> +    VLC_UNUSED(count);
> +    vout_display_sys_t *sys = vd->sys;
> +    picture_sys_t *psys;
> +    picture_resource_t rsc;
> +    int i;
> +
> +    if (!sys->pool && !sys->picture) {
> +        memset(&rsc, 0, sizeof(rsc));
> +
> +        for (i = 0; i < PICTURE_PLANE_MAX; i++) {
> +            rsc.p[i].p_pixels = sys->map[0]+sys->offsets[i];
> +            rsc.p[i].i_lines  = sys->height;
> +            rsc.p[i].i_pitch  = sys->stride;
> +        }
> +
> +        psys = calloc(1, sizeof(*psys));
> +        if (psys == NULL)
> +            return NULL;
> +
> +        psys->p_voutsys = sys;
> +        rsc.p_sys = psys;
> +        rsc.pf_destroy = CustomDestroyPicture;
> +
> +        sys->picture = picture_NewFromResource(&vd->fmt, &rsc);
> +
> +        if (!sys->picture) {
> +            free((void*)psys);
> +            return NULL;
> +        }
> +
> +        sys->pool = picture_pool_New(1, &sys->picture);
> +        if (!sys->pool)
> +            picture_Release(sys->picture);
> +    }
> +
> +    return sys->pool;
> +}
> +
> +
> +static void Display(vout_display_t *vd, picture_t *picture,
> +                    subpicture_t *subpicture)
> +{
> +    VLC_UNUSED(subpicture);
> +    vout_display_sys_t *sys = vd->sys;
> +    int i;
> +
> +    if (drmModeSetPlane(sys->drm_fd, sys->plane_id, sys->crtc,
> +                         sys->fb[sys->front_buf], 1<<1,
> +                         0, 0, sys->width, sys->height,
> +                         0, 0, sys->width << 16, sys->height << 16))
> +    {
> +        msg_Err(vd, "Cannot do set plane for plane id %u, fb %x",
> +                sys->plane_id,
> +                sys->fb[sys->front_buf]);
> +    } else {
> +        sys->front_buf++;
> +        sys->front_buf %= MAXHWBUF;
> +
> +        for (i = 0; i < PICTURE_PLANE_MAX; i++)
> +            sys->picture->p[i].p_pixels =
> +                    sys->map[sys->front_buf]+sys->offsets[i];

Are you switching buffers in the single pool picture here ? IMO it would 
be cleaner to use MAXHWBUF pictures in the pool and let the picture pool 
do its job. You won't have to manage the front_buf yourself.
> +    }
> +    picture_Release(picture);
> +}
> +
> +
> +/**
> + * This function allocates and initializes a KMS vout method.
> + */
> +static int Open(vlc_object_t *object)
> +{
> +    vout_display_t *vd = (vout_display_t *)object;
> +    vout_display_sys_t *sys;
> +    vlc_fourcc_t local_vlc_chroma;
> +    uint32_t local_drm_chroma;
> +    video_format_t fmt = {};
> +    char *chroma;
> +
> +    if (vout_display_IsWindowed(vd))
> +        return VLC_EGENERIC;
> +
> +    /*
> +     * Allocate instance and initialize some members
> +     */
> +    vd->sys = sys = calloc(1, sizeof(*sys));

Use vlc_obj_calloc().

> +    if (!sys)
> +        return VLC_ENOMEM;
> +
> +    sys->pool = NULL;
> +    sys->drm_fourcc = 0;
> +    sys->vlc_fourcc = 0;

calloc already sets everything to 0

> +
> +    chroma = var_InheritString(vd, "kms-vlc-chroma");
> +    if (chroma) {
> +        local_vlc_chroma = vlc_fourcc_GetCodecFromString(VIDEO_ES, chroma);
> +
> +        if (local_vlc_chroma) {
> +            sys->vlc_fourcc = local_vlc_chroma;
> +            msg_Dbg(vd, "Forcing VLC to use chroma '%4s'", chroma);
> +         } else {
> +            sys->vlc_fourcc = vd->fmt.i_chroma;
> +            msg_Dbg(vd, "Chroma %4s invalid, using default", chroma);
> +         }
> +
> +        free(chroma);
> +        chroma = NULL;
> +    } else {
> +        sys->vlc_fourcc = vd->fmt.i_chroma;
> +        msg_Dbg(vd, "Chroma %4s invalid, using default", chroma);
> +    }
> +
> +    chroma = var_InheritString(vd, "kms-drm-chroma");
> +    if (chroma) {
> +        local_drm_chroma = VLC_FOURCC(chroma[0], chroma[1], chroma[2],
> +                                      chroma[3]);
> +
> +        if (local_drm_chroma) {
> +            sys->forced_drm_fourcc = true;
> +            sys->drm_fourcc = local_drm_chroma;
> +            msg_Dbg(vd, "Setting DRM chroma to '%4s'", chroma);
> +        }
> +        else
> +            msg_Dbg(vd, "Chroma %4s invalid, using default", chroma);
> +
> +        free(chroma);
> +        chroma = NULL;
> +    }
> +
> +    if (OpenDisplay(vd)) {

!= VLC_SUCCESS is more readable

> +        Close(VLC_OBJECT(vd));
> +        return VLC_EGENERIC;
> +    }
> +
> +    video_format_ApplyRotation(&fmt, &vd->fmt);
> +
> +    fmt.i_width = fmt.i_visible_width  = sys->width;
> +    fmt.i_height = fmt.i_visible_height = sys->height;
> +    fmt.i_chroma = sys->vlc_fourcc;
> +
> +    vd->fmt     = fmt;
> +    vd->pool    = Pool;
> +    vd->prepare = NULL;
> +    vd->display = Display;
> +    vd->control = Control;
> +
> +    vout_window_ReportSize(vd->cfg->window, sys->width, sys->height);
> +    return VLC_SUCCESS;
> +}
> +
> +
> +static void CloseDisplay(vout_display_t *vd)
> +{
> +    vout_display_sys_t *sys = vd->sys;
> +
> +    if (sys->pool)
> +        picture_pool_Release(sys->pool);
> +
> +    if (sys->drm_fd)
> +        drmDropMaster(sys->drm_fd);
> +
> +    free(sys);
> +}
> +
> +
> +/**
> + * Terminate an output method created by Open
> + */
> +static void Close(vlc_object_t *object)
> +{
> +    vout_display_t *vd = (vout_display_t *)object;
> +
> +    CloseDisplay(vd);
> +}



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