> On Dec 18, 2024, at 12:23, Scott Theisen <scott.the....@gmail.com> wrote:
>
> On 12/17/24 11:10, Zhao Zhili wrote:
>>> On Dec 17, 2024, at 06:48, Scott Theisen <scott.the....@gmail.com> wrote:
>>>
>>> On 12/15/24 22:15, Zhao Zhili wrote:
>>>>> On Dec 15, 2024, at 12:14, Scott Theisen<scott.the....@gmail.com> wrote:
>>>>>
>>>>> Based on patches by Lukas Rusak from
>>>>> https://github.com/lrusak/FFmpeg/commits/v4l2-drmprime-v4
>>>>>
>>>>> libavcodec: v4l2m2m: output AVDRMFrameDescriptor
>>>>> https://github.com/lrusak/FFmpeg/commit/2cb8052ac65a56d8a3f347a1e6f12d4449a5a614
>>>>>
>>>>> libavcodec: v4l2m2m: depends on libdrm
>>>>> https://github.com/lrusak/FFmpeg/commit/ab4cf3e6fb37cffdebccca52e36a7b2deb7e729f
>>>>>
>>>>> libavcodec: v4l2m2m: set format_modifier to DRM_FORMAT_MOD_LINEAR
>>>>> https://github.com/lrusak/FFmpeg/commit/9438a6efa29c7c7ec80c39c9b013b9a12d7b5f33
>>>>>
>>>>> libavcodec: v4l2m2m: only mmap the buffer when it is output type and drm
>>>>> prime is used
>>>>> https://github.com/lrusak/FFmpeg/commit/093656607863e47630de2d1cfcf0ac8e4b93a69e
>>>>>
>>>>> libavcodec: v4l2m2m: allow using software pixel formats
>>>>> https://github.com/lrusak/FFmpeg/commit/8405b573e83838e6b2fea99825fbef32ee9f7767
>>>>>
>>>>> libavcodec: v4l2m2m: implement hwcontext
>>>>> https://github.com/lrusak/FFmpeg/commit/b2c1f1eb39b54bf034497a7f2a7f23855d0a7cde
>>>>>
>>>>> libavcodec: v4l2m2m: implement flush
>>>>> https://github.com/lrusak/FFmpeg/commit/e793ef82727d6d6f55c40844463d476e7e84efad
>>>>>
>>>>> Originally added to MythTV in:
>>>>> FFmpeg: Patch FFmpeg for V4L2 codecs DRM PRIME support
>>>>> https://github.com/MythTV/mythtv/commit/cc7572f9b26189ad5d5d504c05f08e53e4e61b54
>>>>>
>>>>> FFmpeg: Re-apply v4l2 memory to memory DRM_PRIME support
>>>>> https://github.com/MythTV/mythtv/commit/1c942720591b5b7820abe9ed0d805afabbdffe3c
>>>>>
>>>>> modified in:
>>>>> V4L2 Codecs: Fix lockup when seeking
>>>>> https://github.com/MythTV/mythtv/commit/fdc0645aba9a9ad373888bd62ebcbc83a3feb7e5
>>>>>
>>>>> v4l2_buffers: Add some libdrm ifdef's
>>>>> https://github.com/MythTV/mythtv/commit/336df1067abfa4fe7cf611541e5b6f3561fc81a2
>>>>>
>>>>> !!!!
>>>>> NB: libavcodec/v4l2_m2m_dec.c: v4l2_decode_init(): I'm returning -1
>>>>> since I don't know what error code I should use.
>>>>>
>>>>> Note also Lucas Rusak's v5 series:
>>>>> closer diff to current state, otherwise unchanged
>>>>> libavcodec: v4l2m2m: output AVDRMFrameDescriptor
>>>>> https://github.com/lrusak/FFmpeg/commit/c6b85ed30f06ea99513b13cc768a922ebe4d68c2
>>>>>
>>>>> new option:
>>>>> libavcodec: v4l2m2m: add option to specify pixel format used by the
>>>>> decoder
>>>>> https://github.com/lrusak/FFmpeg/commit/ffc4419f456c00ab71cf93f792b0473c6de14e64
>>>>>
>>>>> additional code vs v4
>>>>> libavcodec: v4l2m2m: implement flush
>>>>> https://github.com/lrusak/FFmpeg/commit/8595d06d4909bbec0aa14625fcfc869c6bcef696
>>>>> ---
>>>>> configure | 1 +
>>>>> libavcodec/v4l2_buffers.c | 206 +++++++++++++++++++++++++++++++++++---
>>>>> libavcodec/v4l2_buffers.h | 4 +
>>>>> libavcodec/v4l2_context.c | 43 +++++++-
>>>>> libavcodec/v4l2_context.h | 2 +
>>>>> libavcodec/v4l2_m2m.h | 5 +
>>>>> libavcodec/v4l2_m2m_dec.c | 62 ++++++++++++
>>>>> 7 files changed, 305 insertions(+), 18 deletions(-)
>>>>>
>>>>> diff --git a/configure b/configure
>>>>> index bf55ba67fa..5f02cf3b51 100755
>>>>> --- a/configure
>>>>> +++ b/configure
>>>>> @@ -3770,6 +3770,7 @@ sndio_indev_deps="sndio"
>>>>> sndio_outdev_deps="sndio"
>>>>> v4l2_indev_deps_any="linux_videodev2_h sys_videoio_h"
>>>>> v4l2_indev_suggest="libv4l2"
>>>>> +v4l2_outdev_deps="libdrm"
>>>> Why v4l2_outdev when the patch is for libavcodec?
>>> Lukas Rusak appears to have only submitted up to v3 of his patches in 2018.
>>>
>>> This appears to be from a comment in
>>> https://patchwork.ffmpeg.org/project/ffmpeg/patch/4bbeff66-6123-9296-5775-96d75809e...@jkqxz.net/
>>>
>>> However, with the `#if CONFIG_LIBDRM`s added by Mark Kendall for MythTV, I
>>> don't think it is a hard dependency.
>>>
>>> ...
>>>>> diff --git a/libavcodec/v4l2_m2m_dec.c b/libavcodec/v4l2_m2m_dec.c
>>>>> index aa2d759e1e..cfeee7f2fb 100644
>>>>> --- a/libavcodec/v4l2_m2m_dec.c
>>>>> +++ b/libavcodec/v4l2_m2m_dec.c
>>>>> @@ -23,12 +23,17 @@
>>>>>
>>>>> #include <linux/videodev2.h>
>>>>> #include <sys/ioctl.h>
>>>>> +
>>>>> +#include "libavutil/hwcontext.h"
>>>>> +#include "libavutil/hwcontext_drm.h"
>>>>> #include "libavutil/pixfmt.h"
>>>>> #include "libavutil/pixdesc.h"
>>>>> #include "libavutil/opt.h"
>>>>> #include "libavcodec/avcodec.h"
>>>>> #include "codec_internal.h"
>>>>> #include "libavcodec/decode.h"
>>>>> +#include "libavcodec/internal.h"
>>>>> +#include "libavcodec/hwconfig.h"
>>>>>
>>>>> #include "v4l2_context.h"
>>>>> #include "v4l2_m2m.h"
>>>>> @@ -205,7 +210,44 @@ static av_cold int v4l2_decode_init(AVCodecContext
>>>>> *avctx)
>>>>> capture->av_codec_id = AV_CODEC_ID_RAWVIDEO;
>>>>> capture->av_pix_fmt = avctx->pix_fmt;
>>>>>
>>>>> + /* the client requests the codec to generate DRM frames:
>>>>> + * - data[0] will therefore point to the returned
>>>>> AVDRMFrameDescriptor
>>>>> + * check the ff_v4l2_buffer_to_avframe conversion function.
>>>>> + * - the DRM frame format is passed in the DRM frame descriptor
>>>>> layer.
>>>>> + * check the v4l2_get_drm_frame function.
>>>>> + */
>>>>> + {
>>>>> + const enum AVPixelFormat *pix_fmts = NULL;
>>>>> + int num_pix_fmts = 0;
>>>>> + ret = avcodec_get_supported_config(avctx, NULL,
>>>>> AV_CODEC_CONFIG_PIX_FORMAT,
>>>>> + 0, (const void **) &pix_fmts,
>>>>> &num_pix_fmts);
>>>> I don’t think here is the meant use case for avcodec_get_supported_config.
>>>> Specify available pixel format directly in pix_fmts.
>>>>
>>>>> + if (ret < 0)
>>>>> + return ret;
>>>>> + if (pix_fmts == NULL || num_pix_fmts < 1)
>>>>> + return -1;
>>>> There is no which error code to use issue after remove
>>>> avcodec_get_supported_config.
>>>>
>>> AVCodec::pix_fmts was deprecated, so I replaced it with
>>> avcodec_get_supported_config() in
>>> https://github.com/ulmus-scott/FFmpeg/commit/7ac4b4fc2282b4fdda78ffb1a446ceb85b681661
>>>
>>> Was that incorrect?
>> Firstly, AVCodec::pix_fmts was deprecated, which should be replaced by
>> FFCodec::get_supported_config
>> callback for **internal implementation**. avcodec_get_supported_config is
>> towards for libavcodec API users.
>
> I don't see any problem with calling the public API internally.
>
>> Secondly, AVCodec::pix_fmts and FFCodec::get_supported_config is for
>> **encoder**. For decoder, it’s
>> AVCodecContext::get_format callback to do the negotiate, for example,
>> h264_slice.c get_pixel_format().
>
> OK, the list would only conditionally contain AV_PIX_FMT_DRM_PRIME then?
The list should contain AV_PIX_FMT_DRM_PRIME and the soft pixel format.
>
>>
>>>>> + switch (ff_get_format(avctx, pix_fmts)) {
>>>>> + case AV_PIX_FMT_DRM_PRIME:
>>>>> + s->output_drm = 1;
>>>>> + break;
>>>>> + case AV_PIX_FMT_NONE:
>>>>> + return 0;
>>>>> + break;
>>>> Why return 0 for AV_PIX_FMT_NONE? It’s suspicious.
>>>> ‘break’ can be removed.
>>> That is from
>>> https://github.com/lrusak/FFmpeg/commit/8405b573e83838e6b2fea99825fbef32ee9f7767
>>>
>>> I agree return 0 is strange. All I can say is that is what the code used
>>> by MythTV is and has been for years. (Maybe MythTV always requests
>>> AV_PIX_FMT_DRM_PRIME?)
>>>
>>> This change is not used by MythTV but maybe
>>> https://github.com/lrusak/FFmpeg/commit/ffc4419f456c00ab71cf93f792b0473c6de14e64
>>> is related or an alternate way of requesting the pixel format?
>>>
>>>>> + default:
>>>>> + break;
>>>>> + }
>>>>> + }
>
> As the change currently stands, I think this is equivalent to `s->output_drm
> = 1;`.
>
>>>>> +
>>>>> + s->device_ref = av_hwdevice_ctx_alloc(AV_HWDEVICE_TYPE_DRM);
>>>>> + if (!s->device_ref) {
>>>>> + ret = AVERROR(ENOMEM);
>>>>> + return ret;
>>>>> + }
>>>> I’m not sure whether there is use case to let user specify device?
>>> This is from
>>> https://github.com/lrusak/FFmpeg/commit/b2c1f1eb39b54bf034497a7f2a7f23855d0a7cde
>>>
>>> I don't know what you mean by "let user specify device".
>> User can create a DRM hw device directly via hwcontext API, and provided to
>> decoder via
>> AVCodecContext::hw_device_ctx. It don’t looks right to always create hw
>> device directly inside
>> the decoder implementation.
>
> rkmppdec.c always creates its own hardware device context.
It’s not a good reference.
>
>>
>>>>> +
>>>>> s->avctx = avctx;
>>>>> + ret = av_hwdevice_ctx_init(s->device_ref);
>>>>> + if (ret < 0)
>>>>> + return ret;
>>>>> +
>>>>> ret = ff_v4l2_m2m_codec_init(priv);
>>>>> if (ret) {
>>>>> av_log(avctx, AV_LOG_ERROR, "can't configure decoder\n");
>
> So are you saying this should require the user to create the hardware context
> before calling avcodec_open2()? And the change would then be something like
> this:
It’s “optional” for user to create the hardware context.
> ```
> s->output_drm = 0;
> #if CONFIG_LIBDRM
> if (avctx->hw_device_ctx != NULL &&
> ((AVHWDeviceContext*)avctx->hw_device_ctx->data)->type ==
> AV_HWDEVICE_TYPE_DRM)
> s->output_drm = 1;
> #endif
> ```
>
> What about AVCodecContext::hw_frames_ctx?
See the comments on AV_CODEC_HW_CONFIG_METHOD_HW_DEVICE_CTX,
AV_CODEC_HW_CONFIG_METHOD_HW_FRAMES_CTX,
and so on.
You can take coviddec.c as reference. I just found it missing the
AV_CODEC_HW_CONFIG_METHOD_HW_FRAMES_CTX flag, but the
implementation is fine.
https://ffmpeg.org/pipermail/ffmpeg-devel/2024-December/337624.html
>
>>>>> @@ -220,6 +262,16 @@ static av_cold int v4l2_decode_close(AVCodecContext
>>>>> *avctx)
>>>>> return ff_v4l2_m2m_codec_end(avctx->priv_data);
>>>>> }
>>>>>
>>>>> +static void v4l2_flush(AVCodecContext *avctx)
>>>>> +{
>>>>> + V4L2m2mPriv *priv = avctx->priv_data;
>>>>> + V4L2m2mContext* s = priv->context;
>>>>> +
>>>>> + /* wait for pending buffer references */
>>>>> + if (atomic_load(&s->refcount))
>>>>> + while(sem_wait(&s->refsync) == -1 && errno == EINTR);
>>>>> +}
>>>> Does refcount depends on users behavior like holding a frame? Is it
>>>> possible to run into deadlock here, e.g.,
>>>> user request flush while holding some frames?
>>> I don't know, but Lukas Rusak removed that in his v5 patch (not used by
>>> MythTV)
>>> https://github.com/lrusak/FFmpeg/commit/8595d06d4909bbec0aa14625fcfc869c6bcef696
>>>
>>> Original v4 patch for reference:
>>> https://github.com/lrusak/FFmpeg/commit/e793ef82727d6d6f55c40844463d476e7e84efad
>>>
>>>>> +
>>>>> #define OFFSET(x) offsetof(V4L2m2mPriv, x)
>>>>> #define FLAGS AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_DECODING_PARAM
>>>>>
>>>>> @@ -230,6 +282,11 @@ static const AVOption options[] = {
>>>>> { NULL},
>>>>> };
>>>>>
>>>>> +static const AVCodecHWConfigInternal *v4l2_m2m_hw_configs[] = {
>>>>> + HW_CONFIG_INTERNAL(DRM_PRIME),
>>>> Depends on whether allow user to specify drm device.
>>> This is from the main patch
>>> https://github.com/lrusak/FFmpeg/commit/2cb8052ac65a56d8a3f347a1e6f12d4449a5a614
>>>
>>> Unless this is used internally by FFmpeg, MythTV does not appear to use it.
>>>
>
> Regards,
>
> Scott Theisen
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