linux-kernel - Re: [PATCH v3 07/23] media: atmel: atmel-isc-base: use streaming status when queueing buffers

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Message-ID: <c6adb59e-4554-dc08-3772-148eb22c29ba@xs4all.nl>
Date:   Tue, 11 Jan 2022 16:53:40 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Eugen Hristev <eugen.hristev@...rochip.com>,
        linux-media@...r.kernel.org, robh+dt@...nel.org, jacopo@...ndi.org,
        laurent.pinchart@...asonboard.com, sakari.ailus@....fi
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        nicolas.ferre@...rochip.com
Subject: Re: [PATCH v3 07/23] media: atmel: atmel-isc-base: use streaming
 status when queueing buffers

On 13/12/2021 14:49, Eugen Hristev wrote:
> During experiments with libcamera, it looks like vb2_is_streaming returns
> true before our start streaming is called.
> Order of operations is streamon -> queue -> start_streaming
> ISC would have started the DMA immediately when a buffer is being added
> to the vbqueue if the queue is streaming.
> It is more safe to start the DMA after the start streaming of the driver is
> called.
> Thus, even if vb2queue is streaming, add the buffer to the dma queue of the
> driver instead of actually starting the DMA process, if the start streaming
> has not been called yet.
> 
> Signed-off-by: Eugen Hristev <eugen.hristev@...rochip.com>
> ---
>  drivers/media/platform/atmel/atmel-isc-base.c | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/media/platform/atmel/atmel-isc-base.c b/drivers/media/platform/atmel/atmel-isc-base.c
> index 26a6090f056c..e6c9071c04f0 100644
> --- a/drivers/media/platform/atmel/atmel-isc-base.c
> +++ b/drivers/media/platform/atmel/atmel-isc-base.c
> @@ -441,12 +441,14 @@ static void isc_buffer_queue(struct vb2_buffer *vb)
>  	unsigned long flags;
>  
>  	spin_lock_irqsave(&isc->dma_queue_lock, flags);
> -	if (!isc->cur_frm && list_empty(&isc->dma_queue) &&
> -		vb2_is_streaming(vb->vb2_queue)) {
> +
> +	if (!isc->cur_frm && list_empty(&isc->dma_queue) && !isc->stop) {
>  		isc->cur_frm = buf;
>  		isc_start_dma(isc);
> -	} else
> +	} else {
>  		list_add_tail(&buf->list, &isc->dma_queue);
> +	}
> +
>  	spin_unlock_irqrestore(&isc->dma_queue_lock, flags);
>  }

Both the old and new code doesn't make a lot of sense.

buf_queue is only called by vb2 if start_streaming has already been called or is
about to be called.

Typically all that the buf_queue op does is to call list_add_tail(&buf->list, &isc->dma_queue);
inside the spinlock.

>  
> @@ -1014,7 +1016,7 @@ static int isc_s_fmt_vid_cap(struct file *file, void *priv,
>  {
>  	struct isc_device *isc = video_drvdata(file);
>  
> -	if (vb2_is_streaming(&isc->vb2_vidq))
> +	if (!isc->stop)

This is weird as well. Normally this calls vb2_is_busy to check if the
queue is busy (that really means that buffers are already allocated, so
changing the format isn't allowed anymore).

>  		return -EBUSY;
>  
>  	return isc_set_fmt(isc, f);
> @@ -1536,7 +1538,7 @@ static int isc_s_awb_ctrl(struct v4l2_ctrl *ctrl)
>  
>  		isc_update_awb_ctrls(isc);
>  
> -		if (vb2_is_streaming(&isc->vb2_vidq)) {
> +		if (!isc->stop) {

Ditto.

>  			/*
>  			 * If we are streaming, we can update profile to
>  			 * have the new settings in place.
> @@ -1552,8 +1554,7 @@ static int isc_s_awb_ctrl(struct v4l2_ctrl *ctrl)
>  		}
>  
>  		/* if we have autowhitebalance on, start histogram procedure */
> -		if (ctrls->awb == ISC_WB_AUTO &&
> -		    vb2_is_streaming(&isc->vb2_vidq) &&
> +		if (ctrls->awb == ISC_WB_AUTO && !isc->stop &&
>  		    ISC_IS_FORMAT_RAW(isc->config.sd_format->mbus_code))
>  			isc_set_histogram(isc, true);
>  
> @@ -1829,6 +1830,8 @@ static int isc_async_complete(struct v4l2_async_notifier *notifier)
>  	struct vb2_queue *q = &isc->vb2_vidq;
>  	int ret = 0;
>  
> +	isc->stop = true;
> +

I'm really not sure that you need the stop bool at all.

>  	INIT_WORK(&isc->awb_work, isc_awb_work);
>  
>  	ret = v4l2_device_register_subdev_nodes(&isc->v4l2_dev);

Regards,

	Hans