linux-kernel - [PATCH] exynos: drm: use monotonic timestamps

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Message-Id: <20171102114415.1811842-1-arnd@arndb.de>
Date:   Thu,  2 Nov 2017 12:43:54 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Inki Dae <inki.dae@...sung.com>,
        Joonyoung Shim <jy0922.shim@...sung.com>,
        Seung-Woo Kim <sw0312.kim@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        David Airlie <airlied@...ux.ie>
Cc:     Arnd Bergmann <arnd@...db.de>, Kukjin Kim <kgene@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Tobias Jakobi <tjakobi@...h.uni-bielefeld.de>,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] exynos: drm: use monotonic timestamps

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@...db.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 */
-- 
2.9.0