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

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Date:   Wed, 29 Mar 2023 17:08:43 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     "Sahin, Okan" <Okan.Sahin@...log.com>
Cc:     Nuno Sá <noname.nuno@...il.com>,
        Mark Brown <broonie@...nel.org>, 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, Mar 28, 2023 at 04:01:21PM +0000, Sahin, Okan 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?

> Actually, I do not want to disable regmap lock that's why I did not update it.

If you have something like 

func1()
	regmap_read(reg1)
	regmap_read/write(reg2)

func2()
	regmap_read/write(regX) // X may or may not be 1 or 2

and func1() and func2() can be run in parallel then the code is racy.

Do you have such in your code?

-- 
With Best Regards,
Andy Shevchenko