linux-kernel - Re: [Linux-stm32] [PATCH] pwm: stm32: Fix the usage of uninitialized variable in stm32_pwm

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Date:   Fri, 4 Oct 2019 22:08:04 +0200
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Benjamin GAIGNARD <benjamin.gaignard@...com>
Cc:     Yizhuo <yzhai003@....edu>,
        "linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Fabrice GASNIER <fabrice.gasnier@...com>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [Linux-stm32] [PATCH] pwm: stm32: Fix the usage of uninitialized
 variable in stm32_pwm_config()

Hello,

Cc += Mark Brown who maintains regmap

On Fri, Oct 04, 2019 at 09:09:51AM +0000, Benjamin GAIGNARD wrote:
> 
> On 10/4/19 8:23 AM, Uwe Kleine-König wrote:
> > Hello,
> >
> > On Thu, Oct 03, 2019 at 09:46:49PM -0700, Yizhuo wrote:
> >> Inside function stm32_pwm_config(), variable "psc" and " arr"
> >> could be uninitialized if regmap_read() returns -EINVALs.
> >> However, they are used later in the if statement to decide
> >> the return value which is potentially unsafe.
> 
> Hi Yizhuo,
> 
> like for the your patch in IIO trigger regmap_read could only failed
> if the hardware block is no more clocked and in this case we won't 
> return of regmap_read.

I'm not sure this is aligned with how regmap is supposed to be used. I
think the driver making use of regmap is not supposed to make any
assumptions about how and when a read or write access can or cannot fail
and instead is supposed to check all return values. So IMHO the patch
goes in the right direction.

> Testing regmap_read() return value just add code but doesn't provide a 
> valid information.
> If you really want to log all the possible errors cases please do it in 
> regmap code itself and
> not in *all* the drivers.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |