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

[Michal Wajdeczko <michal.wajdeczko@intel.com>]

On 12.10.2024 07:09, Matthew Brost wrote:
> 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@intel.com>
>> Signed-off-by: Shuicheng Lin <shuicheng.lin@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?

note that in upcoming series [1] there will be no error code returned

[1] https://patchwork.freedesktop.org/series/137982/#rev9

> 
>>  	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
>>