drm/xe: Handle unreliable MMIO reads during forcewake

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 and return failure.
The force wake failure log level is changed from notice to err
to match the failure return value.

v2 (Matt Brost):
- set ret value (-EIO) to kick the error to upper layers
v3 (Rodrigo):
- add commit message for the log level promotion from notice to err
v4:
- update reviewed info

Suggested-by: Alex Zuo <[e-mail]>
Signed-off-by: Shuicheng Lin <[e-mail]>
Cc: Matthew Brost <[e-mail]>
Cc: Michal Wajdeczko <[e-mail]>
Reviewed-by: Himal Prasad Ghimiray <[e-mail]>
Acked-by: Badal Nilawar <[e-mail]>
Cc: Anshuman Gupta <[e-mail]>
Cc: Matt Roper <[e-mail]>
Cc: Rodrigo Vivi <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]
Signed-off-by: Rodrigo Vivi <[e-mail]>
(cherry picked from commit a9fbeabe7226a3bf90f82d0e28a02c18e3c67447)
Signed-off-by: Lucas De Marchi <[e-mail]>

drivers/gpu/drm/xe/xe_force_wake.c

···
 			     XE_FORCE_WAKE_ACK_TIMEOUT_MS * USEC_PER_MSEC,
 			     &value, true);
 	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),
-			     domain->reg_ack.addr, value);
+		xe_gt_err(gt, "Force wake domain %d failed to ack %s (%pe) reg[%#x] = %#x\n",
+			  domain->id, str_wake_sleep(wake), ERR_PTR(ret),
+			  domain->reg_ack.addr, value);
+	if (value == ~0) {
+		xe_gt_err(gt,
+			  "Force wake domain %d: %s. MMIO unreliable (forcewake register returns 0xFFFFFFFF)!\n",
+			  domain->id, str_wake_sleep(wake));
+		ret = -EIO;
+	}
 
 	return ret;
 }