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gpu: host1x: Skip redundant syncpoint loads in host1x_syncpt_wait()

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In host1x_syncpt_wait(), the hardware syncpoint value was loaded
initially for expiry check, and then loaded a second time to
populate the caller's value pointer. Reuse a single load for
both purposes.

After dma_fence_wait_timeout(), the previous code reloaded the syncpoint
value for the expiry check, which is only required in the timeout case.
On success (i.e., return value > 0, or return value == 0 with zero
jiffies remaining), the ISR has already cached the value before
signaling the fence. The value pointer can therefore be populated using
the cached value using host1x_syncpt_read_min() without MMIO access.
Only the timeout path requires a fresh load, move host1x_syncpt_load()
under that path.

Measured Syncpoint wait latency (50000 samples):
  Average latency:   12.2 us  -> 10.6 us
  99.99 pct latency: 62.96 us -> 51.90 us

Signed-off-by: Tanmay Patil <tanmayp@nvidia.com>
Acked-by: Mikko Perttunen <mperttunen@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patch.msgid.link/20260514103153.766343-2-tanmayp@nvidia.com
This commit is contained in:
Tanmay Patil 2026-05-14 10:31:52 +00:00 committed by Thierry Reding
parent 3cbf5e3c46
commit 6fea41ff36
1 changed files with 14 additions and 9 deletions
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23
drivers/gpu/host1x/syncpt.c
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@ -222,11 +222,12 @@ int host1x_syncpt_wait(struct host1x_syncpt *sp, u32 thresh, long timeout,
{
struct dma_fence *fence;
long wait_err;
u32 curr;
host1x_hw_syncpt_load(sp->host, sp);
curr = host1x_syncpt_load(sp);
if (value)
*value = host1x_syncpt_load(sp);
*value = curr;
if (host1x_syncpt_is_expired(sp, thresh))
return 0;
@ -245,21 +246,25 @@ int host1x_syncpt_wait(struct host1x_syncpt *sp, u32 thresh, long timeout,
host1x_fence_cancel(fence);
dma_fence_put(fence);
if (value)
*value = host1x_syncpt_load(sp);
/*
* Don't rely on dma_fence_wait_timeout return value,
* since it returns zero both on timeout and if the
* wait completed with 0 jiffies left.
*/
host1x_hw_syncpt_load(sp->host, sp);
if (wait_err == 0 && !host1x_syncpt_is_expired(sp, thresh))
if (wait_err == 0 && !host1x_syncpt_is_expired(sp, thresh)) {
if (value)
*value = host1x_syncpt_load(sp);
return -EAGAIN;
else if (wait_err < 0)
} else if (wait_err < 0) {
return wait_err;
else
} else {
/* Success, read the value cached by ISR */
if (value)
*value = host1x_syncpt_read_min(sp);
return 0;
}
}
EXPORT_SYMBOL(host1x_syncpt_wait);