exynos: drm: use monotonic timestamps

Submitted by Arnd Bergmann on Nov. 2, 2017, 11:43 a.m.

Details

Message ID 20171102114415.1811842-1-arnd@arndb.de
State New
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Series "exynos: drm: use monotonic timestamps" ( rev: 1 ) in DRI devel

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Commit Message

Arnd Bergmann Nov. 2, 2017, 11:43 a.m.
The exynos DRM driver uses real-time 'struct timeval' values
for exporting its timestamps to user space. This has multiple
problems:

1. signed seconds overflow in y2038
2. the 'struct timeval' definition is deprecated in the kernel
3. time may jump or go backwards after a 'settimeofday()' syscall
4. other DRM timestamps are in CLOCK_MONOTONIC domain, so they
   can't be compared
5. exporting microseconds requires a division by 1000, which may
   be slow on some architectures.

Ideally timestamps should just use 64-bit nanoseconds instead, but
of course we can't change that now. Instead, this tries to address
the first four points above by using monotonic 'timespec' values.

The downside is that there is a small risk of breaking user space
if that expects the absolute timestamp numbers to relate to the
result of 'gettimeofday()'. Please review the user space driver
before applying this patch to ensure this works.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/gpu/drm/exynos/exynos_drm_g2d.c | 6 +++---
 drivers/gpu/drm/exynos/exynos_drm_ipp.c | 8 ++++----
 2 files changed, 7 insertions(+), 7 deletions(-)

Patch hide | download patch | download mbox

diff --git a/drivers/gpu/drm/exynos/exynos_drm_g2d.c b/drivers/gpu/drm/exynos/exynos_drm_g2d.c
index 2b8bf2dd6387..9effe40f5fa5 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_g2d.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_g2d.c
@@ -926,7 +926,7 @@  static void g2d_finish_event(struct g2d_data *g2d, u32 cmdlist_no)
 	struct drm_device *drm_dev = g2d->subdrv.drm_dev;
 	struct g2d_runqueue_node *runqueue_node = g2d->runqueue_node;
 	struct drm_exynos_pending_g2d_event *e;
-	struct timeval now;
+	struct timespec64 now;
 
 	if (list_empty(&runqueue_node->event_list))
 		return;
@@ -934,9 +934,9 @@  static void g2d_finish_event(struct g2d_data *g2d, u32 cmdlist_no)
 	e = list_first_entry(&runqueue_node->event_list,
 			     struct drm_exynos_pending_g2d_event, base.link);
 
-	do_gettimeofday(&now);
+	ktime_get_ts64(&now);
 	e->event.tv_sec = now.tv_sec;
-	e->event.tv_usec = now.tv_usec;
+	e->event.tv_usec = now.tv_nsec / NSEC_PER_USEC;
 	e->event.cmdlist_no = cmdlist_no;
 
 	drm_send_event(drm_dev, &e->base);
diff --git a/drivers/gpu/drm/exynos/exynos_drm_ipp.c b/drivers/gpu/drm/exynos/exynos_drm_ipp.c
index 3edda18cc2d2..3f9d8d79bbde 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_ipp.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_ipp.c
@@ -1406,7 +1406,7 @@  static int ipp_send_event(struct exynos_drm_ippdrv *ippdrv,
 	struct drm_exynos_ipp_queue_buf qbuf;
 	struct drm_exynos_ipp_send_event *e;
 	struct list_head *head;
-	struct timeval now;
+	struct timespec64 now;
 	u32 tbuf_id[EXYNOS_DRM_OPS_MAX] = {0, };
 	int ret, i;
 
@@ -1509,10 +1509,10 @@  static int ipp_send_event(struct exynos_drm_ippdrv *ippdrv,
 	e = list_first_entry(&c_node->event_list,
 		struct drm_exynos_ipp_send_event, base.link);
 
-	do_gettimeofday(&now);
-	DRM_DEBUG_KMS("tv_sec[%ld]tv_usec[%ld]\n", now.tv_sec, now.tv_usec);
+	ktime_get_ts64(&now);
+	DRM_DEBUG_KMS("tv_sec[%lld]tv_nsec[%ld]\n", (s64)now.tv_sec, now.tv_nsec);
 	e->event.tv_sec = now.tv_sec;
-	e->event.tv_usec = now.tv_usec;
+	e->event.tv_usec = now.tv_nsec / NSEC_PER_USEC;
 	e->event.prop_id = property->prop_id;
 
 	/* set buffer id about source destination */

Comments

Hello Arnd,

I guess you could coordinate the IPP changes with Marek, who is rewriting the
IPP subsystem anyway (added Marek to Cc).

Here is the most recent IPPv2 series:
https://www.spinics.net/lists/linux-samsung-soc/msg61066.html

Concerning the G2D changes, I don't think anything in userspace uses the
timestamps (e.g. for synchronisation).

With best wishes,
Tobias


Arnd Bergmann wrote:
> The exynos DRM driver uses real-time 'struct timeval' values
> for exporting its timestamps to user space. This has multiple
> problems:
> 
> 1. signed seconds overflow in y2038
> 2. the 'struct timeval' definition is deprecated in the kernel
> 3. time may jump or go backwards after a 'settimeofday()' syscall
> 4. other DRM timestamps are in CLOCK_MONOTONIC domain, so they
>    can't be compared
> 5. exporting microseconds requires a division by 1000, which may
>    be slow on some architectures.
> 
> Ideally timestamps should just use 64-bit nanoseconds instead, but
> of course we can't change that now. Instead, this tries to address
> the first four points above by using monotonic 'timespec' values.
> 
> The downside is that there is a small risk of breaking user space
> if that expects the absolute timestamp numbers to relate to the
> result of 'gettimeofday()'. Please review the user space driver
> before applying this patch to ensure this works.
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/gpu/drm/exynos/exynos_drm_g2d.c | 6 +++---
>  drivers/gpu/drm/exynos/exynos_drm_ipp.c | 8 ++++----
>  2 files changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/exynos/exynos_drm_g2d.c b/drivers/gpu/drm/exynos/exynos_drm_g2d.c
> index 2b8bf2dd6387..9effe40f5fa5 100644
> --- a/drivers/gpu/drm/exynos/exynos_drm_g2d.c
> +++ b/drivers/gpu/drm/exynos/exynos_drm_g2d.c
> @@ -926,7 +926,7 @@ static void g2d_finish_event(struct g2d_data *g2d, u32 cmdlist_no)
>  	struct drm_device *drm_dev = g2d->subdrv.drm_dev;
>  	struct g2d_runqueue_node *runqueue_node = g2d->runqueue_node;
>  	struct drm_exynos_pending_g2d_event *e;
> -	struct timeval now;
> +	struct timespec64 now;
>  
>  	if (list_empty(&runqueue_node->event_list))
>  		return;
> @@ -934,9 +934,9 @@ static void g2d_finish_event(struct g2d_data *g2d, u32 cmdlist_no)
>  	e = list_first_entry(&runqueue_node->event_list,
>  			     struct drm_exynos_pending_g2d_event, base.link);
>  
> -	do_gettimeofday(&now);
> +	ktime_get_ts64(&now);
>  	e->event.tv_sec = now.tv_sec;
> -	e->event.tv_usec = now.tv_usec;
> +	e->event.tv_usec = now.tv_nsec / NSEC_PER_USEC;
>  	e->event.cmdlist_no = cmdlist_no;
>  
>  	drm_send_event(drm_dev, &e->base);
> diff --git a/drivers/gpu/drm/exynos/exynos_drm_ipp.c b/drivers/gpu/drm/exynos/exynos_drm_ipp.c
> index 3edda18cc2d2..3f9d8d79bbde 100644
> --- a/drivers/gpu/drm/exynos/exynos_drm_ipp.c
> +++ b/drivers/gpu/drm/exynos/exynos_drm_ipp.c
> @@ -1406,7 +1406,7 @@ static int ipp_send_event(struct exynos_drm_ippdrv *ippdrv,
>  	struct drm_exynos_ipp_queue_buf qbuf;
>  	struct drm_exynos_ipp_send_event *e;
>  	struct list_head *head;
> -	struct timeval now;
> +	struct timespec64 now;
>  	u32 tbuf_id[EXYNOS_DRM_OPS_MAX] = {0, };
>  	int ret, i;
>  
> @@ -1509,10 +1509,10 @@ static int ipp_send_event(struct exynos_drm_ippdrv *ippdrv,
>  	e = list_first_entry(&c_node->event_list,
>  		struct drm_exynos_ipp_send_event, base.link);
>  
> -	do_gettimeofday(&now);
> -	DRM_DEBUG_KMS("tv_sec[%ld]tv_usec[%ld]\n", now.tv_sec, now.tv_usec);
> +	ktime_get_ts64(&now);
> +	DRM_DEBUG_KMS("tv_sec[%lld]tv_nsec[%ld]\n", (s64)now.tv_sec, now.tv_nsec);
>  	e->event.tv_sec = now.tv_sec;
> -	e->event.tv_usec = now.tv_usec;
> +	e->event.tv_usec = now.tv_nsec / NSEC_PER_USEC;
>  	e->event.prop_id = property->prop_id;
>  
>  	/* set buffer id about source destination */
>
On Fri, Nov 3, 2017 at 3:04 PM, Tobias Jakobi
<tjakobi@math.uni-bielefeld.de> wrote:
> Hello Arnd,
>
> I guess you could coordinate the IPP changes with Marek, who is rewriting the
> IPP subsystem anyway (added Marek to Cc).
>
> Here is the most recent IPPv2 series:
> https://www.spinics.net/lists/linux-samsung-soc/msg61066.html
>
> Concerning the G2D changes, I don't think anything in userspace uses the
> timestamps (e.g. for synchronisation).

I'm cleaning out older patches that didn't make it in yet now, and got to this
one. I looked at the current state and found that the ipp specific half of my
patch is obsolete now, and we won't need to patch anything there with
Marek's new version.

For the G2D half, I'll just resubmit the patch I had here, let's discuss
further from there, if you think we should just drop the timestamp.

Thanks!

       Arnd