linux-kernel - Re: [RESEND PATCH v3] drivers: thermal: tsens: add timeout to get_temp_tsens

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Date:   Thu, 7 Oct 2021 13:08:56 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Ansuel Smith <ansuelsmth@...il.com>
Cc:     Andy Gross <agross@...nel.org>, Amit Kucheria <amitk@...nel.org>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH v3] drivers: thermal: tsens: add timeout to
 get_temp_tsens_valid

On Thu 07 Oct 10:28 PDT 2021, Ansuel Smith wrote:

> The function can loop and lock the system if for whatever reason the bit
> for the target sensor is NEVER valid. This is the case if a sensor is
> disabled by the factory and the valid bit is never reported as actually
> valid. Add a timeout check and exit if a timeout occurs. As this is
> a very rare condition, handle the timeout only if the first read fails.
> While at it also rework the function to improve readability and convert
> to poll_timeout generic macro.
> 

Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>

Regards,
Bjorn

> Signed-off-by: Ansuel Smith <ansuelsmth@...il.com>
> ---
>  drivers/thermal/qcom/tsens.c | 29 ++++++++++++++---------------
>  1 file changed, 14 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/thermal/qcom/tsens.c b/drivers/thermal/qcom/tsens.c
> index b1162e566a70..99a8d9f3e03c 100644
> --- a/drivers/thermal/qcom/tsens.c
> +++ b/drivers/thermal/qcom/tsens.c
> @@ -603,22 +603,21 @@ int get_temp_tsens_valid(const struct tsens_sensor *s, int *temp)
>  	int ret;
>  
>  	/* VER_0 doesn't have VALID bit */
> -	if (tsens_version(priv) >= VER_0_1) {
> -		ret = regmap_field_read(priv->rf[valid_idx], &valid);
> -		if (ret)
> -			return ret;
> -		while (!valid) {
> -			/* Valid bit is 0 for 6 AHB clock cycles.
> -			 * At 19.2MHz, 1 AHB clock is ~60ns.
> -			 * We should enter this loop very, very rarely.
> -			 */
> -			ndelay(400);
> -			ret = regmap_field_read(priv->rf[valid_idx], &valid);
> -			if (ret)
> -				return ret;
> -		}
> -	}
> +	if (tsens_version(priv) == VER_0)
> +		goto get_temp;
> +
> +	/* Valid bit is 0 for 6 AHB clock cycles.
> +	 * At 19.2MHz, 1 AHB clock is ~60ns.
> +	 * We should enter this loop very, very rarely.
> +	 * Wait 1 us since it's the min of poll_timeout macro.
> +	 * Old value was 400 ns.
> +	 */
> +	ret = regmap_field_read_poll_timeout(priv->rf[valid_idx], valid,
> +					     valid, 1, 20 * USEC_PER_MSEC);
> +	if (ret)
> +		return ret;
>  
> +get_temp:
>  	/* Valid bit is set, OK to read the temperature */
>  	*temp = tsens_hw_to_mC(s, temp_idx);
>  
> -- 
> 2.32.0
>