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SubjectRe: [PATCH] [v2] drm/exynos: g2d: use monotonic timestamps


2018년 01월 18일 02:01에 Arnd Bergmann 이(가) 쓴 글:
> 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.
>
> The code existed in two places before, but the IPP portion was
> removed in 8ded59413ccc ("drm/exynos: ipp: Remove Exynos DRM
> IPP subsystem"), so we no longer need to worry about it.
>
> 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.
>
> According to Tobias Jakobi, user space doesn't care about the
> timestamp at the moment, so we can change the format. Even if
> there is something looking at them, it will work just fine with
> monotonic times as long as the application only looks at the
> relative values between two events.
>
> Link: https://patchwork.kernel.org/patch/10038593/
> Cc: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Picked it up.

Thanks,
Inki Dae

> ---
> v2: rebased to what will be in 4.15, now that ipp is gone,
> updated changelog text based on input from Tobias.
> ---
> drivers/gpu/drm/exynos/exynos_drm_g2d.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 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);
>

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