linux-kernel - Re: [PATCH v8 05/14] media: platform: Improve power on and power off flow

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Date:   Thu, 21 May 2020 15:22:53 +0000
From:   Tomasz Figa <tfiga@...omium.org>
To:     Xia Jiang <xia.jiang@...iatek.com>
Cc:     Hans Verkuil <hverkuil-cisco@...all.nl>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Rick Chang <rick.chang@...iatek.com>,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        srv_heupstream@...iatek.com, senozhatsky@...omium.org,
        mojahsu@...omium.org, drinkcat@...omium.org,
        maoguang.meng@...iatek.com, sj.huang@...iatek.com
Subject: Re: [PATCH v8 05/14] media: platform: Improve power on and power off
 flow

Hi Xia,

On Fri, Apr 03, 2020 at 05:40:24PM +0800, Xia Jiang wrote:
> Call pm_runtime_get_sync() before starting a frame and then
> pm_runtime_put() after completing it. This can save power for the time
> between processing two frames.
> 
> Signed-off-by: Xia Jiang <xia.jiang@...iatek.com>
> ---
>  .../media/platform/mtk-jpeg/mtk_jpeg_core.c   | 27 +++++--------------
>  1 file changed, 6 insertions(+), 21 deletions(-)
> 

Thank you for the patch. Please see my comments inline.

> diff --git a/drivers/media/platform/mtk-jpeg/mtk_jpeg_core.c b/drivers/media/platform/mtk-jpeg/mtk_jpeg_core.c
> index a536fa95b3d6..dd5cadd101ef 100644
> --- a/drivers/media/platform/mtk-jpeg/mtk_jpeg_core.c
> +++ b/drivers/media/platform/mtk-jpeg/mtk_jpeg_core.c
> @@ -710,23 +710,6 @@ static struct vb2_v4l2_buffer *mtk_jpeg_buf_remove(struct mtk_jpeg_ctx *ctx,
>  		return v4l2_m2m_dst_buf_remove(ctx->fh.m2m_ctx);
>  }
>  
> -static int mtk_jpeg_start_streaming(struct vb2_queue *q, unsigned int count)
> -{
> -	struct mtk_jpeg_ctx *ctx = vb2_get_drv_priv(q);
> -	struct vb2_v4l2_buffer *vb;
> -	int ret = 0;
> -
> -	ret = pm_runtime_get_sync(ctx->jpeg->dev);
> -	if (ret < 0)
> -		goto err;
> -
> -	return 0;
> -err:
> -	while ((vb = mtk_jpeg_buf_remove(ctx, q->type)))
> -		v4l2_m2m_buf_done(vb, VB2_BUF_STATE_QUEUED);
> -	return ret;
> -}
> -
>  static void mtk_jpeg_stop_streaming(struct vb2_queue *q)
>  {
>  	struct mtk_jpeg_ctx *ctx = vb2_get_drv_priv(q);
> @@ -751,8 +734,6 @@ static void mtk_jpeg_stop_streaming(struct vb2_queue *q)
>  
>  	while ((vb = mtk_jpeg_buf_remove(ctx, q->type)))
>  		v4l2_m2m_buf_done(vb, VB2_BUF_STATE_ERROR);
> -
> -	pm_runtime_put_sync(ctx->jpeg->dev);
>  }
>  
>  static const struct vb2_ops mtk_jpeg_qops = {
> @@ -761,7 +742,6 @@ static const struct vb2_ops mtk_jpeg_qops = {
>  	.buf_queue          = mtk_jpeg_buf_queue,
>  	.wait_prepare       = vb2_ops_wait_prepare,
>  	.wait_finish        = vb2_ops_wait_finish,
> -	.start_streaming    = mtk_jpeg_start_streaming,
>  	.stop_streaming     = mtk_jpeg_stop_streaming,
>  };
>  
> @@ -812,7 +792,7 @@ static void mtk_jpeg_device_run(void *priv)
>  	struct mtk_jpeg_src_buf *jpeg_src_buf;
>  	struct mtk_jpeg_bs bs;
>  	struct mtk_jpeg_fb fb;
> -	int i;
> +	int i, ret;
>  
>  	src_buf = v4l2_m2m_next_src_buf(ctx->fh.m2m_ctx);
>  	dst_buf = v4l2_m2m_next_dst_buf(ctx->fh.m2m_ctx);
> @@ -832,6 +812,10 @@ static void mtk_jpeg_device_run(void *priv)
>  		return;
>  	}
>  
> +	ret = pm_runtime_get_sync(jpeg->dev);
> +	if (ret < 0)
> +		goto dec_end;
> +
>  	mtk_jpeg_set_dec_src(ctx, &src_buf->vb2_buf, &bs);
>  	if (mtk_jpeg_set_dec_dst(ctx, &jpeg_src_buf->dec_param, &dst_buf->vb2_buf, &fb))
>  		goto dec_end;
> @@ -957,6 +941,7 @@ static irqreturn_t mtk_jpeg_dec_irq(int irq, void *priv)
>  	v4l2_m2m_buf_done(src_buf, buf_state);
>  	v4l2_m2m_buf_done(dst_buf, buf_state);
>  	v4l2_m2m_job_finish(jpeg->m2m_dev, ctx->fh.m2m_ctx);
> +	pm_runtime_put_sync(ctx->jpeg->dev);

The _sync variant explicitly waits until the asynchronous PM operation
completes. This is usually undesired, because the CPU stays blocked for
no good reason. In this context it is actually a bug, because this is an
interrupt handler and it's not allowed to sleep. I wonder why this
actually didn't crash in your testing. Please change to the regular
pm_runtime_put().

Best regards,
Tomasz