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

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

On Tue, Sep 29, 2026 at 12:20:37PM -0700, Alan Previn wrote:
> Check for overflow in udelay use in __xe_mmio_wait32 and
> avoid growing delays becoming intollerably large by capping the
> in-loop wait time.
> 
> v7: - Change assisted-by to "LLM" (Rodrigo).
>     - Move the max-wait macro to outside the function (Rodrigo).
> v6: - Fix commit message to remove items dropped in v5. Fix the
>       use of MAX_UDELAY_MS for microsecond unit. (Shasiko review).
> v5: - Simplify: don't introduce additional redesign and
>       use min_t with a backoff to cap wait. (Rodrigo).
> v4: - Simplify using poll_timeout_us and poll_timeout_us_atomic and
>       update all callers to never use a param for atomic (Jani)
> v3: - Use div64_s64 kernel API for 32-bit vs 64-bit division.
> v2: - Fixed checkpatch failure.
>     - Added helper for 64-bit DIV_ROUND_UP on 32-bit CPU (Shasiko
>       review). Fixed bug max range in usleep_range(Shasiko review)
> 
> Fixes: 5c09bd6ccd41 ("drm/xe/mmio: Move xe_mmio_wait32() to xe_mmio.c")
> Signed-off-by: Alan Previn <alan.previn.teres.alexis@intel.com>
> Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Assisted-by: LLM
> ---

pushed to drm-xe-next.

Thanks a lot for the fix and the patience ;)

>  drivers/gpu/drm/xe/xe_mmio.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_mmio.c b/drivers/gpu/drm/xe/xe_mmio.c
> index 7fa18dfcb5a2..455a07d79cd9 100644
> --- a/drivers/gpu/drm/xe/xe_mmio.c
> +++ b/drivers/gpu/drm/xe/xe_mmio.c
> @@ -320,6 +320,7 @@ u64 xe_mmio_read64_2x32(struct xe_mmio *mmio, struct xe_reg reg)
>  	return (u64)udw << 32 | ldw;
>  }
>  
> +#define __XE_MMIO_WAIT_MAX_BACKOFF_100MS (100 * USEC_PER_MSEC)
>  static int __xe_mmio_wait32(struct xe_mmio *mmio, struct xe_reg reg, u32 mask, u32 val,
>  			    u32 timeout_us, u32 *out_val, bool atomic, bool expect_match)
>  {
> @@ -350,10 +351,10 @@ static int __xe_mmio_wait32(struct xe_mmio *mmio, struct xe_reg reg, u32 mask, u
>  			wait = ktime_us_delta(end, cur);
>  
>  		if (atomic)
> -			udelay(wait);
> +			udelay(min_t(s64, wait, (MAX_UDELAY_MS * 1000)));
>  		else
>  			usleep_range(wait, wait << 1);
> -		wait <<= 1;
> +		wait = min_t(s64, wait << 1, __XE_MMIO_WAIT_MAX_BACKOFF_100MS);
>  	}
>  
>  	if (ret != 0) {
> -- 
> 2.43.0
>