[PATCH] drm/xe: Log unreliable MMIO reads during forcewake

[Matthew Brost]

On Sat, Oct 12, 2024 at 03:34:45AM +0000, Shuicheng Lin wrote:
> In some cases, when the driver attempts to read an MMIO register,
> the hardware may return 0xFFFFFFFF. The current force wake path
> code treats this as a valid response, as it only checks the BIT.
> However, 0xFFFFFFFF should be considered an invalid value, indicating
> a potential issue. To address this, we should add a log entry to
> highlight this condition.
> 
> Suggested-by: Alex Zuo <alex.zuo at intel.com>
> Signed-off-by: Shuicheng Lin <shuicheng.lin at intel.com>
> ---
>  drivers/gpu/drm/xe/xe_force_wake.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xe/xe_force_wake.c b/drivers/gpu/drm/xe/xe_force_wake.c
> index a64c14757c84..46f36d05293a 100644
> --- a/drivers/gpu/drm/xe/xe_force_wake.c
> +++ b/drivers/gpu/drm/xe/xe_force_wake.c
> @@ -114,6 +114,10 @@ static int __domain_wait(struct xe_gt *gt, struct xe_force_wake_domain *domain,
>  	ret = xe_mmio_wait32(&gt->mmio, domain->reg_ack, domain->val, wake ? domain->val : 0,
>  			     XE_FORCE_WAKE_ACK_TIMEOUT_MS * USEC_PER_MSEC,
>  			     &value, true);
> +	if (value == ~0)
> +		xe_gt_notice(gt,
> +			     "Force wake domain %d: %s. MMIO unreliable (forcewake register returns 0xFFFFFFFF)!\n",
> +			     domain->id, str_wake_sleep(wake));

Set the ret value (-EIO) to kick the error to upper layers?

>  	if (ret)

Then...

if (ret)
	...
else if (value == ~0)
	...
	ret = -EIO;

Matt

>  		xe_gt_notice(gt, "Force wake domain %d failed to ack %s (%pe) reg[%#x] = %#x\n",
>  			     domain->id, str_wake_sleep(wake), ERR_PTR(ret),
> -- 
> 2.25.1
>