linux-kernel - Re: [PATCH 1/3] dt-bindings: Add a binding for the RPi firmware GPIO driver.

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Message-ID: <CACRpkdYqPXo4xzNQzjQemCpM_dWYn+ZmSBPopRScyR9K1R3cfg@mail.gmail.com>
Date:   Fri, 23 Sep 2016 15:53:38 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Eric Anholt <eric@...olt.net>
Cc:     linux-rpi-kernel <linux-rpi-kernel@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Stephen Warren <swarren@...dotorg.org>,
        Lee Jones <lee@...nel.org>,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
        Alexandre Courbot <gnurou@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Gerd Hoffmann <kraxel@...hat.com>
Subject: Re: [PATCH 1/3] dt-bindings: Add a binding for the RPi firmware GPIO driver.

On Fri, Sep 23, 2016 at 3:08 PM, Eric Anholt <eric@...olt.net> wrote:

> Sort of related: I also worry that we have races with the firmware for
> the platform GPIO bits, since both ARM and firmware are doing RMWs (or,
> even worse, maybe just Ws?) of the registers controlled by the pinctrl
> driver.  Hopefully I can get the firmware to pass control of devices
> like this over to Linux, with firmware making requests to us, but I
> don't know if that will happen and we may need to access other GPIOs
> using this interface :(

For the race with firmware I have no good solutions, it's just one of
those things I guess :(

When two kernel drivers compete about registers, say for example
one driver needs to RMW bits 0-5 and another driver needs to
RMW bits 7-11, the right solution is usually to use syscon
and then regmap-mmio will deal with the concurrency as part
of regmap_update_bits() etc.

Yours,
Linus Walleij