linux-kernel - Re: [PATCH v6 5/5] mfd: max77541: Add ADI MAX77541/MAX77540 PMIC Support

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Date:   Wed, 29 Mar 2023 09:01:30 +0200
From:   Nuno Sá <noname.nuno@...il.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Mark Brown <broonie@...nel.org>,
        "Sahin, Okan" <Okan.Sahin@...log.com>, Lee Jones <lee@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Cosmin Tanislav <demonsingur@...il.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Caleb Connolly <caleb.connolly@...aro.org>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        "Bolboaca, Ramona" <Ramona.Bolboaca@...log.com>,
        ChiYuan Huang <cy_huang@...htek.com>,
        "Tilki, Ibrahim" <Ibrahim.Tilki@...log.com>,
        William Breathitt Gray <william.gray@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        ChiaEn Wu <chiaen_wu@...htek.com>,
        Haibo Chen <haibo.chen@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>
Subject: Re: [PATCH v6 5/5]  mfd: max77541: Add ADI MAX77541/MAX77540 PMIC
 Support

On Tue, 2023-03-28 at 18:47 +0300, Andy Shevchenko wrote:
> On Tue, Mar 28, 2023 at 04:51:18PM +0200, Nuno Sá wrote:
> > On Tue, 2023-03-28 at 17:35 +0300, Andy Shevchenko wrote:
> > > On Tue, Mar 28, 2023 at 04:18:30PM +0200, Nuno Sá wrote:
> > > > On Tue, 2023-03-28 at 14:46 +0100, Mark Brown wrote:
> > > > > On Tue, Mar 28, 2023 at 03:26:44PM +0200, Nuno Sá wrote:
> > > > > 
> > > > > > IIRC, regmap_read() is not really reentrant and it is used
> > > > > > in
> > > > > > the
> > > > > > IIO
> > > > > > driver on the sysfs interface. So, yeah, I think you need
> > > > > > the
> > > > > > regmap
> > > > > > lock and better just leave the config as is. Yes, the lock
> > > > > > is
> > > > > > opt-
> > > > > > out
> > > > > > so let's not disable it :)
> > > > > 
> > > > > All the regmap operations are fully thread safe.
> > > > 
> > > > Even if 'config->disable_locking' is set? I think that is
> > > > what's
> > > > being
> > > > discussed in here...
> > > 
> > > In case the driver has its own lock to serialize IO how on earth
> > > the
> > > regmap
> > > lock is needed. That's what I asked the author of the driver. He
> > > told
> > > the code
> > 
> > Well, if the driver has it's own locking, then sure we do not need
> > regmap's lock...
> > 
> > > doesn't require the regmap lock, and I tend to believe the
> > > author.
> > > So, why to
> > > keep it?
> > 
> > However, if you look at the adc driver, I can see plain
> > regmap_read()
> > calls without any "outside" locking.
> 
> Then author of the code should know what they are doing. Right?
> 

In theory yes, but you know that's not always the case :)

- Nuno Sá