Re: [PATCH] drm/xe/mmio: Fix xe_mmio_wait32() to honor delay/sleep maximums

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Tue, Sep 15, 2026 at 04:00:54PM +0000, Teres Alexis, Alan Previn wrote:
> On Tue, 2026-09-15 at 10:34 +0300, Nikula, Jani wrote:
> > On Mon, 14 Sep 2026, Alan Previn <alan.previn.teres.alexis@intel.com> wrote:
> alan:snip
> > >  int xe_mmio_wait32(struct xe_mmio *mmio, struct xe_reg reg, u32 mask, u32 val, u32 timeout_us,
> > > -		   u32 *out_val, bool atomic)
> > > +		   u32 *out_val)
> > >  {
> > > -	return __xe_mmio_wait32(mmio, reg, mask, val, timeout_us, out_val, atomic, true);
> > > +	u32 read;
> > > +	int ret;
> > > +
> > > +	ret = poll_timeout_us(read = xe_mmio_read32(mmio, reg), (read & mask) == val,
> > > +			      10, timeout_us, false);
> > 
> > You probably do need to let the callers pass in the wait too. 10 us wait
> > with a long timeout is going to be pretty bad.

agreed

> > 
> > 
> alan: okay - perhaps i can make every caller pass in a polling-wait thats a fraction of their wait time.
> (as a starting point since i dont know what's the expected behavior of every caller).
> so perhaps something like "timeout_us << 4" (i.e. 1/16th) but pass in 10 us if its anything smaller than that
> (i.e. smaller than 16 usec).

I think we might be complicating this too much..

what about something simpler like:

#define XE_MMIO_WAIT_MAX_BACKOFF_US   1000

...
-             wait <<= 1;
+             wait = min_t(s64, wait << 1, XE_MMIO_WAIT_MAX_BACKOFF_US);


Also the Fixes tag is not the right one... the bug was there before...

> 
> ...alan