[PATCH] drm: Use raw monotonic clock

[PATCH] drm: Use raw monotonic clock

[Abhilash Jindal]

Wall time obtained from do_gettimeofday is susceptible to sudden jumps due to
user setting the time or due to NTP.

Raw monotonic time is constantly increasing time and isn't affected by NTP
adjustments better suited for comparing two timestamps in short intervals.

Signed-off-by: Abhilash Jindal <klock.android@gmail.com>
---
 drivers/gpu/drm/via/via_drv.h |    2 +-
 drivers/gpu/drm/via/via_irq.c |   14 +++-----------
 2 files changed, 4 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/via/via_drv.h b/drivers/gpu/drm/via/via_drv.h
index ef8c500..7b1b4f2 100644
--- a/drivers/gpu/drm/via/via_drv.h
+++ b/drivers/gpu/drm/via/via_drv.h
@@ -74,7 +74,7 @@ typedef struct drm_via_private {
 	volatile uint32_t *last_pause_ptr;
 	volatile uint32_t *hw_addr_ptr;
 	drm_via_ring_buffer_t ring;
-	struct timeval last_vblank;
+	ktime_t last_vblank;
 	int last_vblank_valid;
 	unsigned usec_per_vblank;
 	atomic_t vbl_received;
diff --git a/drivers/gpu/drm/via/via_irq.c b/drivers/gpu/drm/via/via_irq.c
index 1319433..5a78117 100644
--- a/drivers/gpu/drm/via/via_irq.c
+++ b/drivers/gpu/drm/via/via_irq.c
@@ -88,13 +88,6 @@ static int via_num_unichrome = ARRAY_SIZE(via_unichrome_irqs);
 static int via_irqmap_unichrome[] = {-1, -1, -1, 0, -1, 1};
 
 
-static unsigned time_diff(struct timeval *now, struct timeval *then)
-{
-	return (now->tv_usec >= then->tv_usec) ?
-		now->tv_usec - then->tv_usec :
-		1000000 - (then->tv_usec - now->tv_usec);
-}
-
 u32 via_get_vblank_counter(struct drm_device *dev, int crtc)
 {
 	drm_via_private_t *dev_priv = dev->dev_private;
@@ -110,7 +103,7 @@ irqreturn_t via_driver_irq_handler(int irq, void *arg)
 	drm_via_private_t *dev_priv = (drm_via_private_t *) dev->dev_private;
 	u32 status;
 	int handled = 0;
-	struct timeval cur_vblank;
+	ktime_t cur_vblank;
 	drm_via_irq_t *cur_irq = dev_priv->via_irqs;
 	int i;
 
@@ -118,11 +111,10 @@ irqreturn_t via_driver_irq_handler(int irq, void *arg)
 	if (status & VIA_IRQ_VBLANK_PENDING) {
 		atomic_inc(&dev_priv->vbl_received);
 		if (!(atomic_read(&dev_priv->vbl_received) & 0x0F)) {
-			do_gettimeofday(&cur_vblank);
+			cur_vblank = ktime_get_raw();
 			if (dev_priv->last_vblank_valid) {
 				dev_priv->usec_per_vblank =
-					time_diff(&cur_vblank,
-						  &dev_priv->last_vblank) >> 4;
+				ktime_to_us(ktime_sub(cur_vblank, dev_priv->last_vblank)) >> 4;
 			}
 			dev_priv->last_vblank = cur_vblank;
 			dev_priv->last_vblank_valid = 1;
-- 
1.7.9.5

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Re: [PATCH] drm: Use raw monotonic clock

[Daniel Vetter]

On Tue, Aug 11, 2015 at 11:46:11AM -0400, Abhilash Jindal wrote:
> Wall time obtained from do_gettimeofday is susceptible to sudden jumps due to
> user setting the time or due to NTP.
> 
> Raw monotonic time is constantly increasing time and isn't affected by NTP
> adjustments better suited for comparing two timestamps in short intervals.
> 
> Signed-off-by: Abhilash Jindal <klock.android@gmail.com>

Do you actually have a via card supported by this driver, including the
corresponding userspace stack? Note that the userspace opengl driver for
this has been nuked in upstream mesa years ago ...
-Daniel

> ---
>  drivers/gpu/drm/via/via_drv.h |    2 +-
>  drivers/gpu/drm/via/via_irq.c |   14 +++-----------
>  2 files changed, 4 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/gpu/drm/via/via_drv.h b/drivers/gpu/drm/via/via_drv.h
> index ef8c500..7b1b4f2 100644
> --- a/drivers/gpu/drm/via/via_drv.h
> +++ b/drivers/gpu/drm/via/via_drv.h
> @@ -74,7 +74,7 @@ typedef struct drm_via_private {
>  	volatile uint32_t *last_pause_ptr;
>  	volatile uint32_t *hw_addr_ptr;
>  	drm_via_ring_buffer_t ring;
> -	struct timeval last_vblank;
> +	ktime_t last_vblank;
>  	int last_vblank_valid;
>  	unsigned usec_per_vblank;
>  	atomic_t vbl_received;
> diff --git a/drivers/gpu/drm/via/via_irq.c b/drivers/gpu/drm/via/via_irq.c
> index 1319433..5a78117 100644
> --- a/drivers/gpu/drm/via/via_irq.c
> +++ b/drivers/gpu/drm/via/via_irq.c
> @@ -88,13 +88,6 @@ static int via_num_unichrome = ARRAY_SIZE(via_unichrome_irqs);
>  static int via_irqmap_unichrome[] = {-1, -1, -1, 0, -1, 1};
>  
>  
> -static unsigned time_diff(struct timeval *now, struct timeval *then)
> -{
> -	return (now->tv_usec >= then->tv_usec) ?
> -		now->tv_usec - then->tv_usec :
> -		1000000 - (then->tv_usec - now->tv_usec);
> -}
> -
>  u32 via_get_vblank_counter(struct drm_device *dev, int crtc)
>  {
>  	drm_via_private_t *dev_priv = dev->dev_private;
> @@ -110,7 +103,7 @@ irqreturn_t via_driver_irq_handler(int irq, void *arg)
>  	drm_via_private_t *dev_priv = (drm_via_private_t *) dev->dev_private;
>  	u32 status;
>  	int handled = 0;
> -	struct timeval cur_vblank;
> +	ktime_t cur_vblank;
>  	drm_via_irq_t *cur_irq = dev_priv->via_irqs;
>  	int i;
>  
> @@ -118,11 +111,10 @@ irqreturn_t via_driver_irq_handler(int irq, void *arg)
>  	if (status & VIA_IRQ_VBLANK_PENDING) {
>  		atomic_inc(&dev_priv->vbl_received);
>  		if (!(atomic_read(&dev_priv->vbl_received) & 0x0F)) {
> -			do_gettimeofday(&cur_vblank);
> +			cur_vblank = ktime_get_raw();
>  			if (dev_priv->last_vblank_valid) {
>  				dev_priv->usec_per_vblank =
> -					time_diff(&cur_vblank,
> -						  &dev_priv->last_vblank) >> 4;
> +				ktime_to_us(ktime_sub(cur_vblank, dev_priv->last_vblank)) >> 4;
>  			}
>  			dev_priv->last_vblank = cur_vblank;
>  			dev_priv->last_vblank_valid = 1;
> -- 
> 1.7.9.5
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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