drm_timeout_abs_to_jiffies() covers the drivers whose wait UAPI takes an absolute deadline, but there is no equivalent for the drivers that express a wait as a duration. Drivers such as i915 and v3d convert the value themselves.
Converting a nanosecond duration to jiffies needs some care. nsecs_to_jiffies() returns unsigned long, so on 32-bit a large userspace-supplied timeout overflows its range and is silently truncated. i915 already handles both cases in a local helper, which v3d has a copy of. Add the same conversion to the core, so that it is available to any driver and both copies can be dropped. Signed-off-by: Maíra Canal <[email protected]> --- drivers/gpu/drm/drm_timeout.c | 45 +++++++++++++++++++++++++++++++++++++++++++ include/drm/drm_timeout.h | 1 + 2 files changed, 46 insertions(+) diff --git a/drivers/gpu/drm/drm_timeout.c b/drivers/gpu/drm/drm_timeout.c index 35e10293e0a1..ee545475429c 100644 --- a/drivers/gpu/drm/drm_timeout.c +++ b/drivers/gpu/drm/drm_timeout.c @@ -9,6 +9,7 @@ #include <linux/export.h> #include <linux/jiffies.h> #include <linux/ktime.h> +#include <linux/math64.h> #include <linux/sched.h> #include <drm/drm_timeout.h> @@ -48,3 +49,47 @@ signed long drm_timeout_abs_to_jiffies(int64_t timeout_nsec) return timeout_jiffies64 + 1; } EXPORT_SYMBOL(drm_timeout_abs_to_jiffies); + +/** + * drm_timeout_rel_to_jiffies - calculate jiffies timeout from relative value + * @timeout_nsec: relative timeout in ns, 0 for poll + * + * Calculate the timeout in jiffies from a relative timeout in ns, for drivers + * whose UAPI expresses a wait as a duration rather than as a deadline. + * + * The result is clamped to MAX_JIFFY_OFFSET. That keeps it positive once it is + * converted to the signed long taken by dma_fence_wait_timeout() and friends, + * which matters on 32-bit, and keeps it distinct from MAX_SCHEDULE_TIMEOUT so + * that a finite wait is never understood as an infinite one. + * + * It's strongly discouraged to use relative timeouts in uAPIs, as they do not + * survive a restarted ioctl. A signal-interrupted ioctl is re-entered with the + * same arguments, so the duration starts counting from zero again. New uAPIs + * should take an absolute deadline and use drm_timeout_abs_to_jiffies(). + * + * Returns: + * 0 if @timeout_nsec is 0. Otherwise the equivalent number of jiffies and + * clamped to MAX_JIFFY_OFFSET. + */ +unsigned long drm_timeout_rel_to_jiffies(u64 timeout_nsec) +{ + u64 secs; + u32 rem; + + /* Make 0 timeout means poll, as for the absolute variant. */ + if (timeout_nsec == 0) + return 0; + + /* + * As nsecs_to_jiffies64() does not guard against overflow, split + * the timeout into whole seconds and nanoseconds. This way + * nsecs_to_jiffies64() is always handed a value below a second. + */ + secs = div_u64_rem(timeout_nsec, NSEC_PER_SEC, &rem); + if (secs >= MAX_JIFFY_OFFSET / HZ) + return MAX_JIFFY_OFFSET; + + return min_t(u64, MAX_JIFFY_OFFSET, + secs_to_jiffies(secs) + nsecs_to_jiffies64(rem) + 1); +} +EXPORT_SYMBOL(drm_timeout_rel_to_jiffies); diff --git a/include/drm/drm_timeout.h b/include/drm/drm_timeout.h index cd9621c52062..6ee222a3e97c 100644 --- a/include/drm/drm_timeout.h +++ b/include/drm/drm_timeout.h @@ -12,5 +12,6 @@ #include <linux/types.h> signed long drm_timeout_abs_to_jiffies(s64 timeout_nsec); +unsigned long drm_timeout_rel_to_jiffies(u64 timeout_nsec); #endif -- 2.55.0
