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authorArnd Bergmann <arnd@arndb.de>2017-10-11 17:20:12 +0200
committerDave Airlie <airlied@redhat.com>2017-10-13 08:34:46 +1000
commit67680d3c046450b3901aa4e5a9cf2f8fbd7ed9a2 (patch)
treee62cd147951abc2b077336a1bd3157115bd192e8 /include
parentc5c7bc71a0e6bc382744497e45c6c70503f9d7e6 (diff)
drm: vblank: use ktime_t instead of timeval
The drm vblank handling uses 'timeval' to store timestamps in either monotonic or wall-clock time base. In either case, it reads the current time as a ktime_t in get_drm_timestamp() and converts it from there. This is a bit suspicious, as users of 'timeval' often suffer from the time_t overflow in y2038. I have gone through this code and found that it is unlikely to cause problems here: - The user space ABI does not use time_t or timeval, but uses 'u32' and 'long' as the types. This means at least that rebuilding user programs against a new libc with 64-bit time_t does not change the ABI. - As of commit c61eef726a78 ("drm: add support for monotonic vblank timestamps") in linux-3.8, the monotonic timestamp is the default and can only get reverted to wall-clock through a module-parameter. - With the default monotonic timestamps, there is no problem at all. - The drm_wait_vblank_ioctl() interface is alway safe on 64-bit architectures, on 32-bit it might overflow the 'long' timestamps in 2038 with wall-clock timestamps. - The event handling uses 'u32' seconds, which overflow in 2106 on both 32-bit and 64-bit machines, when wall-clock timestamps are used. - The effect of overflowing either of the two is only temporary (during the overflow, and is likely to keep working again afterwards. It is likely the same problem as observing a 'settimeofday()' call, which was the reason for moving to the monotonic timestamps in the first place. Overall, this seems good enough, so my patch removes the use of 'timeval' from the vblank handling altogether and uses ktime_t consistently, except for the part where we copy the data to user space structures in the existing format. Signed-off-by: Arnd Bergmann <arnd@arndb.de> Reviewed-by: Sean Paul <seanpaul@chromium.org> Reviewed-by: Keith Packard <keithp@keithp.com> Signed-off-by: Dave Airlie <airlied@redhat.com>
Diffstat (limited to 'include')
-rw-r--r--include/drm/drm_drv.h2
-rw-r--r--include/drm/drm_vblank.h6
2 files changed, 4 insertions, 4 deletions
diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
index ee06ecd6c01f..412e83a4d3db 100644
--- a/include/drm/drm_drv.h
+++ b/include/drm/drm_drv.h
@@ -324,7 +324,7 @@ struct drm_driver {
*/
bool (*get_vblank_timestamp) (struct drm_device *dev, unsigned int pipe,
int *max_error,
- struct timeval *vblank_time,
+ ktime_t *vblank_time,
bool in_vblank_irq);
/**
diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h
index 7fba9efe4951..6a58e2e91a0f 100644
--- a/include/drm/drm_vblank.h
+++ b/include/drm/drm_vblank.h
@@ -92,7 +92,7 @@ struct drm_vblank_crtc {
/**
* @time: Vblank timestamp corresponding to @count.
*/
- struct timeval time;
+ ktime_t time;
/**
* @refcount: Number of users/waiters of the vblank interrupt. Only when
@@ -154,7 +154,7 @@ struct drm_vblank_crtc {
int drm_vblank_init(struct drm_device *dev, unsigned int num_crtcs);
u32 drm_crtc_vblank_count(struct drm_crtc *crtc);
u32 drm_crtc_vblank_count_and_time(struct drm_crtc *crtc,
- struct timeval *vblanktime);
+ ktime_t *vblanktime);
void drm_crtc_send_vblank_event(struct drm_crtc *crtc,
struct drm_pending_vblank_event *e);
void drm_crtc_arm_vblank_event(struct drm_crtc *crtc,
@@ -172,7 +172,7 @@ u32 drm_crtc_accurate_vblank_count(struct drm_crtc *crtc);
bool drm_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev,
unsigned int pipe, int *max_error,
- struct timeval *vblank_time,
+ ktime_t *vblank_time,
bool in_vblank_irq);
void drm_calc_timestamping_constants(struct drm_crtc *crtc,
const struct drm_display_mode *mode);

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