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

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Date:   Tue, 6 Nov 2018 15:10:49 +0000
From:   Kieran Bingham <kieran.bingham@...asonboard.com>
To:     Laurent Pinchart <laurent.pinchart@...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 Laurent,

On 30/07/2018 20:57, Laurent Pinchart wrote:
> 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,

I think code should talk louder than comments (especially as it provides
runtime verification and assertions when lockdep is enabled) - so I've
gone for Philipp's suggestion here.

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

Collected, thanks.


>>  static const struct vb2_ops uvc_queue_qops = {
> 

-- 
Regards
--
Kieran