linux-kernel - Re: [PATCH v2 2/2] drivers: thermal: tsens: add timeout to get_tem_tsens

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Message-ID: <YUR2wmcMMWtoLDGB@Ansuel-xps.localdomain>
Date:   Fri, 17 Sep 2021 13:06:42 +0200
From:   Ansuel Smith <ansuelsmth@...il.com>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Amit Kucheria <amitk@...nel.org>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        Zhang Rui <rui.zhang@...el.com>, linux-arm-msm@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] drivers: thermal: tsens: add timeout to
 get_tem_tsens_valid

On Fri, Sep 17, 2021 at 11:08:15AM +0200, Daniel Lezcano wrote:
> On 07/09/2021 23:25, 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.
> > 
> > Signed-off-by: Ansuel Smith <ansuelsmth@...il.com>
> > ---
> >  drivers/thermal/qcom/tsens.c | 40 +++++++++++++++++++++++-------------
> >  1 file changed, 26 insertions(+), 14 deletions(-)
> > 
> > diff --git a/drivers/thermal/qcom/tsens.c b/drivers/thermal/qcom/tsens.c
> > index b1162e566a70..1ff244176beb 100644
> > --- a/drivers/thermal/qcom/tsens.c
> > +++ b/drivers/thermal/qcom/tsens.c
> > @@ -599,26 +599,38 @@ int get_temp_tsens_valid(const struct tsens_sensor *s, int *temp)
> >  	int hw_id = s->hw_id;
> >  	u32 temp_idx = LAST_TEMP_0 + hw_id;
> >  	u32 valid_idx = VALID_0 + hw_id;
> > +	unsigned long timeout;
> >  	u32 valid;
> >  	int ret;
> >  
> >  	/* VER_0 doesn't have VALID bit */
> > -	if (tsens_version(priv) >= VER_0_1) {
> > +	if (tsens_version(priv) == VER_0)
> > +		goto get_temp;
> > +
> > +	ret = regmap_field_read(priv->rf[valid_idx], &valid);
> > +	if (ret || valid)
> > +		goto check_valid;
> > +
> > +	timeout = jiffies + msecs_to_jiffies(20);
> 
> Why not use regmap_field_read_poll_timeout() ?
>

Ok will convert this to pool_timeout and send v3.
Thx for the review.

> > +	do {
> > +		/* 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;
> > -		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 (ret || valid)
> > +			goto check_valid;
> > +	} while (time_before(jiffies, timeout));
> > +
> > +	return -ETIMEDOUT;
> > +
> > +check_valid:
> > +	/* Check ret of valid bit read */
> > +	if (ret)
> > +		return ret;
> >  
> > +get_temp:
> >  	/* Valid bit is set, OK to read the temperature */
> >  	*temp = tsens_hw_to_mC(s, temp_idx);
> >  
> > 
> 
> 
> -- 
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