On 9/13/24 12:14, Oleksandr Ocheretnyi wrote:
Commit da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake
PCH iTCO") does not mask NMI_NOW bit during TCO1_CNT register's
value comparison for update_no_reboot_bit() call causing following
failure:
...
iTCO_vendor_support: vendor-support=0
iTCO_wdt iTCO_wdt: unable to reset NO_REBOOT flag, device
disabled by hardware/BIOS
...
and this can lead to unexpected NMIs later during regular
crashkernel's workflow because of watchdog probe call failures.
This change masks NMI_NOW bit for TCO1_CNT register values to
avoid unexpected NMI_NOW bit inversions.
Fixes: da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake PCH iTCO")
Signed-off-by: Oleksandr Ocheretnyi <oocheret@xxxxxxxxx>
Reviewed-by: Guenter Roeck <linux@xxxxxxxxxxxx>
---
V2 -> V3: Removed not necessary variable 'mask', updated multi-line comments
V1 -> V2: Provided comments and macro define with bit description
drivers/watchdog/iTCO_wdt.c | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)
diff --git a/drivers/watchdog/iTCO_wdt.c b/drivers/watchdog/iTCO_wdt.c
index 264857d314da..dd297dcd524c 100644
--- a/drivers/watchdog/iTCO_wdt.c
+++ b/drivers/watchdog/iTCO_wdt.c
@@ -82,6 +82,13 @@
#define TCO2_CNT(p) (TCOBASE(p) + 0x0a) /* TCO2 Control Register */
#define TCOv2_TMR(p) (TCOBASE(p) + 0x12) /* TCOv2 Timer Initial Value*/
+/*
+ * NMI_NOW is bit 8 of TCO1_CNT register
+ * Read/Write
+ * This bit is implemented as RW but has no effect on HW.
+ */
+#define NMI_NOW BIT(8)
+
/* internal variables */
struct iTCO_wdt_private {
struct watchdog_device wddev;
@@ -219,13 +226,23 @@ static int update_no_reboot_bit_cnt(void *priv, bool set)
struct iTCO_wdt_private *p = priv;
u16 val, newval;
- val = inw(TCO1_CNT(p));
+ /*
+ * writing back 1b1 to NMI_NOW of TCO1_CNT register
+ * causes NMI_NOW bit inversion what consequently does
+ * not allow to perform the register's value comparison
+ * properly.
+ *
+ * NMI_NOW bit masking for TCO1_CNT register values
+ * helps to avoid possible NMI_NOW bit inversions on
+ * following write operation.
+ */
+ val = inw(TCO1_CNT(p)) & ~NMI_NOW;
if (set)
val |= BIT(0);
else
val &= ~BIT(0);
outw(val, TCO1_CNT(p));
- newval = inw(TCO1_CNT(p));
+ newval = inw(TCO1_CNT(p)) & ~NMI_NOW;
/* make sure the update is successful */
return val != newval ? -EIO : 0;
