linux-kernel - Re: [PATCH v4 4/6] media: uvcvideo: queue: Simplify spin-lock usage

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Date:   Mon, 30 Jul 2018 22:57:00 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Kieran Bingham <kieran.bingham@...asonboard.com>
Cc:     linux-media@...r.kernel.org,
        Guennadi Liakhovetski <g.liakhovetski@....de>,
        Olivier BRAUN <olivier.braun@...reolabs.com>,
        Troy Kisky <troy.kisky@...ndarydevices.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Philipp Zabel <philipp.zabel@...il.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 4/6] media: uvcvideo: queue: Simplify spin-lock usage

Hi Kieran,

Thank you for the patch.

On Tuesday, 27 March 2018 19:46:01 EEST Kieran Bingham wrote:
> Both uvc_start_streaming(), and uvc_stop_streaming() are called from
> userspace context, with interrupts enabled. As such, they do not need to
> save the IRQ state, and can use spin_lock_irq() and spin_unlock_irq()
> respectively.
> 
> Signed-off-by: Kieran Bingham <kieran.bingham@...asonboard.com>
> 
> ---
> 
> v4:
>  - Rebase to v4.16 (linux-media/master)
> 
>  drivers/media/usb/uvc/uvc_queue.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_queue.c
> b/drivers/media/usb/uvc/uvc_queue.c index adcc4928fae4..698d9a5a5aae 100644
> --- a/drivers/media/usb/uvc/uvc_queue.c
> +++ b/drivers/media/usb/uvc/uvc_queue.c
> @@ -169,7 +169,6 @@ static int uvc_start_streaming(struct vb2_queue *vq,
> unsigned int count) {
>  	struct uvc_video_queue *queue = vb2_get_drv_priv(vq);
>  	struct uvc_streaming *stream = uvc_queue_to_stream(queue);
> -	unsigned long flags;
>  	int ret;
> 
>  	queue->buf_used = 0;
> @@ -178,9 +177,9 @@ static int uvc_start_streaming(struct vb2_queue *vq,
> unsigned int count) if (ret == 0)
>  		return 0;
> 
> -	spin_lock_irqsave(&queue->irqlock, flags);
> +	spin_lock_irq(&queue->irqlock);
>  	uvc_queue_return_buffers(queue, UVC_BUF_STATE_QUEUED);
> -	spin_unlock_irqrestore(&queue->irqlock, flags);
> +	spin_unlock_irq(&queue->irqlock);
> 
>  	return ret;
>  }
> @@ -188,14 +187,13 @@ static int uvc_start_streaming(struct vb2_queue *vq,
> unsigned int count) static void uvc_stop_streaming(struct vb2_queue *vq)
>  {
>  	struct uvc_video_queue *queue = vb2_get_drv_priv(vq);
> -	unsigned long flags;
> 
>  	if (vq->type != V4L2_BUF_TYPE_META_CAPTURE)
>  		uvc_video_enable(uvc_queue_to_stream(queue), 0);
> 
> -	spin_lock_irqsave(&queue->irqlock, flags);
> +	spin_lock_irq(&queue->irqlock);
>  	uvc_queue_return_buffers(queue, UVC_BUF_STATE_ERROR);
> -	spin_unlock_irqrestore(&queue->irqlock, flags);
> +	spin_unlock_irq(&queue->irqlock);
>  }

I think you missed my comment that stated

> Please add a one-line comment above both functions to state
>
> /* Must be called with interrupts enabled. */

Philipp Zabel commented that you could also add lockdep_assert_irqs_enabled(), 
and I think that's a good idea. I'll let you decide whether to do both, or 
only add lockdep_assert_irqs_enabled(), I'm fine with either option.

With this fixed,

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

>  static const struct vb2_ops uvc_queue_qops = {

-- 
Regards,

Laurent Pinchart