Re: [PATCH] counter: stm32-lptimer-cnt: fix the check on arr and cmp registers update

From: William Breathitt Gray <william.gray@linaro.org>
To: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Cc: jic23@kernel.org, alexandre.torgue@foss.st.com,
	olivier.moysan@foss.st.com, linux-iio@vger.kernel.org,
	linux-stm32@st-md-mailman.stormreply.com,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] counter: stm32-lptimer-cnt: fix the check on arr and cmp registers update
Date: Tue, 22 Nov 2022 02:27:50 -0500	[thread overview]
Message-ID: <Y3x59hNekCDuOFXT@fedora> (raw)
In-Reply-To: <20221123133609.465614-1-fabrice.gasnier@foss.st.com>

[-- Attachment #1.1: Type: text/plain, Size: 1637 bytes --]

On Wed, Nov 23, 2022 at 02:36:09PM +0100, Fabrice Gasnier wrote:
> The ARR (auto reload register) and CMP (compare) registers are
> successively written. The status bits to check the update of these
> registers are polled together with regmap_read_poll_timeout().
> The condition to end the loop may become true, even if one of the register
> isn't correctly updated.
> So ensure both status bits are set before clearing them.
> 
> Fixes: d8958824cf07 ("iio: counter: Add support for STM32 LPTimer")
> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
> ---
>  drivers/counter/stm32-lptimer-cnt.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/counter/stm32-lptimer-cnt.c b/drivers/counter/stm32-lptimer-cnt.c
> index d6b80b6dfc28..8439755559b2 100644
> --- a/drivers/counter/stm32-lptimer-cnt.c
> +++ b/drivers/counter/stm32-lptimer-cnt.c
> @@ -69,7 +69,7 @@ static int stm32_lptim_set_enable_state(struct stm32_lptim_cnt *priv,
>  
>  	/* ensure CMP & ARR registers are properly written */
>  	ret = regmap_read_poll_timeout(priv->regmap, STM32_LPTIM_ISR, val,
> -				       (val & STM32_LPTIM_CMPOK_ARROK),
> +				       (val & STM32_LPTIM_CMPOK_ARROK) == STM32_LPTIM_CMPOK_ARROK,

This is a reasonable fix, but I don't like seeing so much happening in
an argument list -- it's easy to misunderstand what's going on which can
lead to further bugs the future. Pull out this condition to a dedicated
bool variable with a comment explaining why we need the equivalence
check (i.e. to ensure both status bits are set and not just one).

William Breathitt Gray

[-- Attachment #1.2: signature.asc --]
[-- Type: application/pgp-signature, Size: 228 bytes --]

[-- Attachment #2: Type: text/plain, Size: 176 bytes --]

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel