On Wed, 16 Sep 2026, Jani Nikula <[email protected]> wrote: > On Tue, 15 Sep 2026, Maíra Canal <[email protected]> wrote: >> 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); > > The signed/unsigned differences here bug me a little. Maybe explain why > in the commit message if there's a rationale? > > I note that drm_timeout_rel_to_jiffies() return value is assigned to > unsigned long variables half the time. I guess its kernel-doc could say > it never returns negative values?
Gah, I meant drm_timeout_abs_to_jiffies() here, sorry. > > BR, > Jani. > > > > >> >> #endif -- Jani Nikula, Intel
