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

[Shuicheng Lin <shuicheng.lin@intel.com>]

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));
 	if (ret)
 		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