diff mbox series

[v2] iTCO_wdt: mask NMI_NOW bit for update_no_reboot_bit() call

Message ID 20240912141931.2447826-1-oocheret@cisco.com
State New
Headers show
Series [v2] iTCO_wdt: mask NMI_NOW bit for update_no_reboot_bit() call | expand

Commit Message

Oleksandr Ocheretnyi Sept. 12, 2024, 2:19 p.m. UTC
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@cisco.com>
---
 drivers/watchdog/iTCO_wdt.c | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

Comments

Guenter Roeck Sept. 12, 2024, 9:15 p.m. UTC | #1
On 9/12/24 07:19, 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@cisco.com>
> ---

Oh, and change log goes here.

Guenter
kernel test robot Sept. 13, 2024, 7:58 a.m. UTC | #2
Hi Oleksandr,

kernel test robot noticed the following build warnings:

[auto build test WARNING on westeri-thunderbolt/next]
[also build test WARNING on linus/master v6.11-rc7 next-20240912]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Oleksandr-Ocheretnyi/iTCO_wdt-mask-NMI_NOW-bit-for-update_no_reboot_bit-call/20240912-222231
base:   https://git.kernel.org/pub/scm/linux/kernel/git/westeri/thunderbolt.git next
patch link:    https://lore.kernel.org/r/20240912141931.2447826-1-oocheret%40cisco.com
patch subject: [PATCH v2] iTCO_wdt: mask NMI_NOW bit for update_no_reboot_bit() call
config: i386-buildonly-randconfig-001-20240913 (https://download.01.org/0day-ci/archive/20240913/202409131548.X0MGdN1r-lkp@intel.com/config)
compiler: clang version 18.1.8 (https://github.com/llvm/llvm-project 3b5b5c1ec4a3095ab096dd780e84d7ab81f3d7ff)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240913/202409131548.X0MGdN1r-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202409131548.X0MGdN1r-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> drivers/watchdog/iTCO_wdt.c:226:27: warning: implicit conversion from 'unsigned long' to 'u16' (aka 'unsigned short') changes value from 4294967039 to 65279 [-Wconstant-conversion]
     226 |         u16 val, newval, mask = (~NMI_NOW);
         |                          ~~~~    ^~~~~~~~
   1 warning generated.


vim +226 drivers/watchdog/iTCO_wdt.c

   222	
   223	static int update_no_reboot_bit_cnt(void *priv, bool set)
   224	{
   225		struct iTCO_wdt_private *p = priv;
 > 226		u16 val, newval, mask = (~NMI_NOW);
   227	
   228		/* writing back 1b1 to NMI_NOW of TCO1_CNT register
   229		 * causes NMI_NOW bit inversion what consequently does
   230		 * not allow to perform the register's value comparison
   231		 * properly.
   232		 *
   233		 * NMI_NOW bit masking for TCO1_CNT register values
   234		 * helps to avoid possible NMI_NOW bit inversions on
   235		 * following write operation.
   236		 */
   237		val = inw(TCO1_CNT(p)) & mask;
   238		if (set)
   239			val |= BIT(0);
   240		else
   241			val &= ~BIT(0);
   242		outw(val, TCO1_CNT(p));
   243		newval = inw(TCO1_CNT(p)) & mask;
   244	
   245		/* make sure the update is successful */
   246		return val != newval ? -EIO : 0;
   247	}
   248
diff mbox series

Patch

diff --git a/drivers/watchdog/iTCO_wdt.c b/drivers/watchdog/iTCO_wdt.c
index 264857d314da..46c09359588f 100644
--- a/drivers/watchdog/iTCO_wdt.c
+++ b/drivers/watchdog/iTCO_wdt.c
@@ -82,6 +82,12 @@ 
 #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;
@@ -217,15 +223,24 @@  static int update_no_reboot_bit_mem(void *priv, bool set)
 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));
+	u16 val, newval, mask = (~NMI_NOW);
+
+	/* 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)) & mask;
 	if (set)
 		val |= BIT(0);
 	else
 		val &= ~BIT(0);
 	outw(val, TCO1_CNT(p));
-	newval = inw(TCO1_CNT(p));
+	newval = inw(TCO1_CNT(p)) & mask;
 
 	/* make sure the update is successful */
 	return val != newval ? -EIO : 0;