Re: [RFT PATCH v3 4/6] uvcvideo: queue: Simplify spin-lock usage

[Philipp Zabel]

On Tue, 2018-01-16 at 19:23 +0200, Laurent Pinchart wrote:
> Hi Kieran,
> 
> Thank you for the patch.
> 
> On Friday, 12 January 2018 11:19:26 EET Kieran Bingham wrote:
> > Both uvc_start_streaming(), and uvc_stop_streaming() are called from
> > userspace context. As such, they do not need to save the IRQ state, and
> > can use spin_lock_irq() and spin_unlock_irq() respectively.
> 
> Note that userspace context isn't enough, the key part is that they're called 
> with interrupts enabled. If they were called from userspace context but under 
> a spin_lock_irq() you couldn't use spin_unlock_irq() in those functions.
> 
> > Signed-off-by: Kieran Bingham 
> > ---
> >  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 4a581d631525..ddac4d89a291 100644
> > --- a/drivers/media/usb/uvc/uvc_queue.c
> > +++ b/drivers/media/usb/uvc/uvc_queue.c
> > @@ -158,7 +158,6 @@ 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;
> > @@ -167,9 +166,9 @@ static int uvc_start_streaming(struct vb2_queue *vq,
> > unsigned int count) if (ret == 0)
> > return 0;
> > 
> > -   spin_lock_irqsave(>irqlock, flags);
> > +   spin_lock_irq(>irqlock);
> > uvc_queue_return_buffers(queue, UVC_BUF_STATE_QUEUED);
> > -   spin_unlock_irqrestore(>irqlock, flags);
> > +   spin_unlock_irq(>irqlock);
> > 
> > return ret;
> >  }
> > @@ -178,13 +177,12 @@ static void uvc_stop_streaming(struct vb2_queue *vq)
> >  {
> > struct uvc_video_queue *queue = vb2_get_drv_priv(vq);
> > struct uvc_streaming *stream = uvc_queue_to_stream(queue);
> > -   unsigned long flags;
> > 
> > uvc_video_enable(stream, 0);
> > 
> > -   spin_lock_irqsave(>irqlock, flags);
> > +   spin_lock_irq(>irqlock);
> > uvc_queue_return_buffers(queue, UVC_BUF_STATE_ERROR);
> > -   spin_unlock_irqrestore(>irqlock, flags);
> > +   spin_unlock_irq(>irqlock);
> >  }
> 
> Please add a one-line comment above both functions to state
> 
> /* Must be called with interrupts enabled. */

You could add lockdep_assert_irqs_enabled() as well.

> With this and the commit message updated,
> 
> Reviewed-by: Laurent Pinchart 

regards
Philipp

Re: [RFT PATCH v3 4/6] uvcvideo: queue: Simplify spin-lock usage

[Laurent Pinchart]

Hi Kieran,

Thank you for the patch.

On Friday, 12 January 2018 11:19:26 EET Kieran Bingham wrote:
> Both uvc_start_streaming(), and uvc_stop_streaming() are called from
> userspace context. As such, they do not need to save the IRQ state, and
> can use spin_lock_irq() and spin_unlock_irq() respectively.

Note that userspace context isn't enough, the key part is that they're called 
with interrupts enabled. If they were called from userspace context but under 
a spin_lock_irq() you couldn't use spin_unlock_irq() in those functions.

> Signed-off-by: Kieran Bingham 
> ---
>  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 4a581d631525..ddac4d89a291 100644
> --- a/drivers/media/usb/uvc/uvc_queue.c
> +++ b/drivers/media/usb/uvc/uvc_queue.c
> @@ -158,7 +158,6 @@ 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;
> @@ -167,9 +166,9 @@ static int uvc_start_streaming(struct vb2_queue *vq,
> unsigned int count) if (ret == 0)
>   return 0;
> 
> - spin_lock_irqsave(>irqlock, flags);
> + spin_lock_irq(>irqlock);
>   uvc_queue_return_buffers(queue, UVC_BUF_STATE_QUEUED);
> - spin_unlock_irqrestore(>irqlock, flags);
> + spin_unlock_irq(>irqlock);
> 
>   return ret;
>  }
> @@ -178,13 +177,12 @@ static void uvc_stop_streaming(struct vb2_queue *vq)
>  {
>   struct uvc_video_queue *queue = vb2_get_drv_priv(vq);
>   struct uvc_streaming *stream = uvc_queue_to_stream(queue);
> - unsigned long flags;
> 
>   uvc_video_enable(stream, 0);
> 
> - spin_lock_irqsave(>irqlock, flags);
> + spin_lock_irq(>irqlock);
>   uvc_queue_return_buffers(queue, UVC_BUF_STATE_ERROR);
> - spin_unlock_irqrestore(>irqlock, flags);
> + spin_unlock_irq(>irqlock);
>  }

Please add a one-line comment above both functions to state

/* Must be called with interrupts enabled. */

With this and the commit message updated,

Reviewed-by: Laurent Pinchart 

>  static const struct vb2_ops uvc_queue_qops = {

-- 
Regards,

Laurent Pinchart

[RFT PATCH v3 4/6] uvcvideo: queue: Simplify spin-lock usage

[Kieran Bingham]

Both uvc_start_streaming(), and uvc_stop_streaming() are called from
userspace context. 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 
---
 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 4a581d631525..ddac4d89a291 100644
--- a/drivers/media/usb/uvc/uvc_queue.c
+++ b/drivers/media/usb/uvc/uvc_queue.c
@@ -158,7 +158,6 @@ 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;
@@ -167,9 +166,9 @@ static int uvc_start_streaming(struct vb2_queue *vq, 
unsigned int count)
if (ret == 0)
return 0;
 
-   spin_lock_irqsave(>irqlock, flags);
+   spin_lock_irq(>irqlock);
uvc_queue_return_buffers(queue, UVC_BUF_STATE_QUEUED);
-   spin_unlock_irqrestore(>irqlock, flags);
+   spin_unlock_irq(>irqlock);
 
return ret;
 }
@@ -178,13 +177,12 @@ static void uvc_stop_streaming(struct vb2_queue *vq)
 {
struct uvc_video_queue *queue = vb2_get_drv_priv(vq);
struct uvc_streaming *stream = uvc_queue_to_stream(queue);
-   unsigned long flags;
 
uvc_video_enable(stream, 0);
 
-   spin_lock_irqsave(>irqlock, flags);
+   spin_lock_irq(>irqlock);
uvc_queue_return_buffers(queue, UVC_BUF_STATE_ERROR);
-   spin_unlock_irqrestore(>irqlock, flags);
+   spin_unlock_irq(>irqlock);
 }
 
 static const struct vb2_ops uvc_queue_qops = {
-- 
git-series 0.9.1