Re: [PATCH v4 6/7] media: mediatek: vcodec: replace v4l2_m2m_next_src_buf with v4l2_m2m_src_buf_remove

["Yunfei Dong (董云飞)" <Yunfei.Dong@mediatek.com>]

Hi Sebastian,

Thanks for your suggestion.
On Fri, 2024-08-23 at 17:23 +0200, Sebastian Fricke wrote:
> Hey Yunfei,
> 
> On 07.08.2024 16:24, Yunfei Dong wrote:
> > There isn't lock to protect source buffer when get next src buffer,
> > if the source buffer is removed for some unknown reason before lat
> > work queue execute done, will lead to remove source buffer or
> > buffer
> > done error.
> 
> This is really hard to understand, can try wording this a bit
> clearer?
> Stuff like: if the source buffer is removed ... will lead to remove
> source buffer, just leaves me scratching my head.
> And there is a spinlock in the m2m framework in `v4l2_m2m_next_buf`
> so I
> suppose you mean something else when you say that there is no lock to
> protect the source buffer?
> 
> You might not know all reasons but for this commit description you
> should at least know one reason. Please highlight a case how this can
> happen, so that you can justify the change.
> 
> > 
> > Signed-off-by: Yunfei Dong <yunfei.dong@mediatek.com>
> > ---
> > .../vcodec/decoder/mtk_vcodec_dec_stateless.c | 30 +++++++++++++---
> > ---
> > 1 file changed, 21 insertions(+), 9 deletions(-)
> > 
> > diff --git
> > a/drivers/media/platform/mediatek/vcodec/decoder/mtk_vcodec_dec_sta
> > teless.c
> > b/drivers/media/platform/mediatek/vcodec/decoder/mtk_vcodec_dec_sta
> > teless.c
> > index 8aa379872ddc..3dba3549000a 100644
> > ---
> > a/drivers/media/platform/mediatek/vcodec/decoder/mtk_vcodec_dec_sta
> > teless.c
> > +++
> > b/drivers/media/platform/mediatek/vcodec/decoder/mtk_vcodec_dec_sta
> > teless.c
> > @@ -321,6 +321,7 @@ static void mtk_vdec_worker(struct work_struct
> > *work)
> > 		container_of(work, struct mtk_vcodec_dec_ctx,
> > decode_work);
> > 	struct mtk_vcodec_dec_dev *dev = ctx->dev;
> > 	struct vb2_v4l2_buffer *vb2_v4l2_src = ctx->last_vb2_v4l2_src;
> > +	struct vb2_v4l2_buffer *vb2_v4l2_dst;
> > 	struct vb2_buffer *vb2_src;
> > 	struct mtk_vcodec_mem *bs_src;
> > 	struct mtk_video_dec_buf *dec_buf_src;
> > @@ -329,7 +330,7 @@ static void mtk_vdec_worker(struct work_struct
> > *work)
> > 	bool res_chg = false;
> > 	int ret;
> > 
> > -	vb2_v4l2_src = vb2_v4l2_src ? vb2_v4l2_src :
> > v4l2_m2m_next_src_buf(ctx->m2m_ctx);
> > +	vb2_v4l2_src = vb2_v4l2_src ? vb2_v4l2_src :
> > v4l2_m2m_src_buf_remove(ctx->m2m_ctx);
> > 	if (!vb2_v4l2_src) {
> > 		v4l2_m2m_job_finish(dev->m2m_dev_dec, ctx->m2m_ctx);
> > 		mtk_v4l2_vdec_dbg(1, ctx, "[%d] no available source
> > buffer", ctx->id);
> > @@ -381,17 +382,28 @@ static void mtk_vdec_worker(struct
> > work_struct *work)
> > 	    ctx->current_codec == V4L2_PIX_FMT_VP8_FRAME) {
> > 		if (src_buf_req)
> > 			v4l2_ctrl_request_complete(src_buf_req, &ctx-
> > >ctrl_hdl);
> > -		v4l2_m2m_buf_done_and_job_finish(dev->m2m_dev_dec, ctx-
> > >m2m_ctx, state);
> > -	} else {
> > -		if (ret != -EAGAIN) {
> > -			v4l2_m2m_src_buf_remove(ctx->m2m_ctx);
> > -			ctx->last_vb2_v4l2_src = NULL;
> > -		} else {
> > -			ctx->last_vb2_v4l2_src = vb2_v4l2_src;
> > -		}
> > +		vb2_v4l2_dst = v4l2_m2m_dst_buf_remove(ctx->m2m_ctx);
> > +		v4l2_m2m_buf_done(vb2_v4l2_dst, state);
> > +		v4l2_m2m_buf_done(vb2_v4l2_src, state);
> 
> This is another case where you just remove again completely what you
> have added in the previous patch.
> 
> > 
> > 		v4l2_m2m_job_finish(dev->m2m_dev_dec, ctx->m2m_ctx);
> > +		return;
> > 	}
> > +
> > +	/* If each codec return -EAGAIN to decode again, need to backup
> > current source
> > +	 * buffer, then the driver will get this buffer next time.
> 
> I would reword this like:
> 
> 	/* Store the current source buffer for the next attempt to
> decode,
>     * if this decode returned -EAGAIN */
> 
> > +	 *
> > +	 * If each codec decode error, must to set buffer done with
> > error status for
> > +	 * this buffer have been removed from ready list.
> > +	 */
> > +	ctx->last_vb2_v4l2_src = (ret != -EAGAIN) ? NULL :
> > vb2_v4l2_src;
> 
> Okay and here you add the same thing again as in the previous patch
> but
> differently, this collection of commits feels more and more to me
> like a
> work in progress. Please make sure in the future that each commit
> does
> one job and does it completely.
> It is not only confussing but also makes it hard to read the changes
> as
> the bigger picture is missing in these tiny commits.
> 
> Please try to combine the patches where possible.
> 
Path 5/7 is used to store the source buffer.
path 6/7 is used to handle decoder again when decoder error.

I will check whether it's possible to combine patch 5 and 6 together.

Best Regards,
Yunfei Dong
> Regards,
> Sebastian Fricke
> 
> > +	if (ret && ret != -EAGAIN) {
> > +		if (src_buf_req)
> > +			v4l2_ctrl_request_complete(src_buf_req, &ctx-
> > >ctrl_hdl);
> > +		v4l2_m2m_buf_done(vb2_v4l2_src, state);
> > +	}
> > +
> > +	v4l2_m2m_job_finish(dev->m2m_dev_dec, ctx->m2m_ctx);
> > }
> > 
> > static void vb2ops_vdec_stateless_buf_queue(struct vb2_buffer *vb)
> > -- 
> > 2.46.0
> > 
> >