Re: [PATCH v1] iTCO_wdt: ignore NMI_NOW bit on register comparison

[Mika Westerberg]

Hi,

On Mon, Aug 26, 2024 at 12:53:01AM -0700, Oleksandr Ocheretnyi wrote:
> Commit da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake
> PCH iTCO") does not ignore NMI_NOW bit on write operation to TCO1_CNT
> register what causes unexpected NMIs due to NMI_NOW bit inversion
> during regular crashkernel's workflow with following logs:
> 
> iTCO_vendor_support: vendor-support=0
> iTCO_wdt iTCO_wdt: unable to reset NO_REBOOT flag, device
>                                             disabled by hardware/BIOS
> 
> This change clears NMI_NOW bit in the TCO1_CNT register to have no
> effect on NMI_NOW bit inversion what can cause NMI immediately.
> 
> Fixes: da23b6faa8bf ("watchdog: iTCO: Add support for Cannon Lake PCH iTCO")
> Signed-off-by: Oleksandr Ocheretnyi <oocheret@xxxxxxxxx>
> ---
>  drivers/watchdog/iTCO_wdt.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/watchdog/iTCO_wdt.c b/drivers/watchdog/iTCO_wdt.c
> index 264857d314da..679c115ef7d3 100644
> --- a/drivers/watchdog/iTCO_wdt.c
> +++ b/drivers/watchdog/iTCO_wdt.c
> @@ -224,7 +224,7 @@ static int update_no_reboot_bit_cnt(void *priv, bool set)
>  		val |= BIT(0);
>  	else
>  		val &= ~BIT(0);
> -	outw(val, TCO1_CNT(p));
> +	outw(val & ~BIT(8), TCO1_CNT(p));

I suggest adding some #define for the magical number 8 so that it is
easier for anyone looking at this driver to figure out what it is doing.

Otherwise looks good to me, thanks!

>  	newval = inw(TCO1_CNT(p));
>  
>  	/* make sure the update is successful */
> -- 
> 2.39.3