Re: [PATCH] usb: gadget/uvc: Remove non-required locking from 'uvc_queue_next_buffer' routine

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Hello.

On 22-03-2012 8:50, Bhupesh Sharma wrote:

This patch removes the non-required spinlock acquire/release calls on
'queue_irqlock' from 'uvc_queue_next_buffer' routine.

   'queue->irqlock' maybe?

This routine is called from 'video->encode' function (which translates to either
'uvc_video_encode_bulk' or 'uvc_video_encode_isoc') in 'uvc_video.c'.
As, the 'video->encode' routines are called with 'queue_irqlock' already held,
so acquiring a 'queue_irqlock' again in 'uvc_queue_next_buffer' routine causes
a spin lock recursion.

Signed-off-by: Bhupesh Sharma<bhupesh.sharma@xxxxxx>
Acked-by: Laurent Pinchart<laurent.pinchart@xxxxxxxxxxxxxxxx>
---
  drivers/usb/gadget/uvc_queue.c |    4 +---
  1 files changed, 1 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/gadget/uvc_queue.c b/drivers/usb/gadget/uvc_queue.c
index d776adb..104ae9c 100644
--- a/drivers/usb/gadget/uvc_queue.c
+++ b/drivers/usb/gadget/uvc_queue.c
@@ -543,11 +543,11 @@ done:
  	return ret;
  }

+/* called with &queue_irqlock held.. */

   'queue->irqlock' maybe?

@@ -556,14 +556,12 @@ uvc_queue_next_buffer(struct uvc_video_queue *queue, struct uvc_buffer *buf)
  		return buf;
  	}

-	spin_lock_irqsave(&queue->irqlock, flags);
  	list_del(&buf->queue);
  	if (!list_empty(&queue->irqqueue))
  		nextbuf = list_first_entry(&queue->irqqueue, struct uvc_buffer,
  					   queue);
  	else
  		nextbuf = NULL;
-	spin_unlock_irqrestore(&queue->irqlock, flags);

  	buf->buf.sequence = queue->sequence++;
  	do_gettimeofday(&buf->buf.timestamp);

WBR, Sergei
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