EDAC/igen6: Fix the flood of invalid error reports

The ECC_ERROR_LOG register of certain SoCs may contain the invalid value
~0, which results in a flood of invalid error reports in polling mode.

Fix the flood of invalid error reports by skipping the invalid ECC error
log value ~0.

Fixes: e14232a ("EDAC/igen6: Add polling support")
Reported-by: Ramses <ramses@well-founded.dev>
Closes: https://lore.kernel.org/all/OISL8Rv--F-9@well-founded.dev/
Tested-by: Ramses <ramses@well-founded.dev>
Reported-by: John <therealgraysky@proton.me>
Closes: https://lore.kernel.org/all/p5YcxOE6M3Ncxpn2-Ia_wCt61EM4LwIiN3LroQvT_-G2jMrFDSOW5k2A9D8UUzD2toGpQBN1eI0sL5dSKnkO8iteZegLoQEj-DwQaMhGx4A=@proton.me/
Tested-by: John <therealgraysky@proton.me>
Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Link: https://lore.kernel.org/r/20250212083354.31919-1-qiuxu.zhuo@intel.com

Author: qzhuo2

drivers/edac/igen6_edac.c

@@ -785,13 +785,22 @@ static u64 ecclog_read_and_clear(struct igen6_imc *imc)
 {
 	u64 ecclog = readq(imc->window + ECC_ERROR_LOG_OFFSET);
 
-	if (ecclog & (ECC_ERROR_LOG_CE | ECC_ERROR_LOG_UE)) {
-		/* Clear CE/UE bits by writing 1s */
-		writeq(ecclog, imc->window + ECC_ERROR_LOG_OFFSET);
-		return ecclog;
-	}
+	/*
+	 * Quirk: The ECC_ERROR_LOG register of certain SoCs may contain
+	 *        the invalid value ~0. This will result in a flood of invalid
+	 *        error reports in polling mode. Skip it.
+	 */
+	if (ecclog == ~0)
+		return 0;
 
-	return 0;
+	/* Neither a CE nor a UE. Skip it.*/
+	if (!(ecclog & (ECC_ERROR_LOG_CE | ECC_ERROR_LOG_UE)))
+		return 0;
+
+	/* Clear CE/UE bits by writing 1s */
+	writeq(ecclog, imc->window + ECC_ERROR_LOG_OFFSET);
+
+	return ecclog;
 }
 
 static void errsts_clear(struct igen6_imc *imc)