linux-kernel - Re: [PATCH v5 0/5] gpio: Add GPIO Aggregator

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Date:   Tue, 18 Feb 2020 18:04:27 +0100
From:   Eugeniu Rosca <erosca@...adit-jv.com>
To:     Geert Uytterhoeven <geert+renesas@...der.be>
CC:     Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Jonathan Corbet <corbet@....net>,
        Harish Jenny K N <harish_kandiga@...tor.com>,
        Alexander Graf <graf@...zon.com>,
        Peter Maydell <peter.maydell@...aro.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Phil Reid <preid@...ctromag.com.au>,
        Marc Zyngier <marc.zyngier@....com>,
        Christoffer Dall <christoffer.dall@....com>,
        Magnus Damm <magnus.damm@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        <linux-gpio@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <linux-renesas-soc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <qemu-devel@...gnu.org>,
        Eugeniu Rosca <erosca@...adit-jv.com>,
        Eugeniu Rosca <roscaeugeniu@...il.com>
Subject: Re: [PATCH v5 0/5] gpio: Add GPIO Aggregator

Hi Geert,

On Tue, Feb 18, 2020 at 04:18:07PM +0100, Geert Uytterhoeven wrote:
> 	Hi all,
> 
> GPIO controllers are exported to userspace using /dev/gpiochip*
> character devices.  Access control to these devices is provided by
> standard UNIX file system permissions, on an all-or-nothing basis:
> either a GPIO controller is accessible for a user, or it is not.
> Currently no mechanism exists to control access to individual GPIOs.
> 
> Hence this adds a GPIO driver to aggregate existing GPIOs, and expose
> them as a new gpiochip.  This is useful for implementing access control,
> and assigning a set of GPIOs to a specific user.  Furthermore, this
> simplifies and hardens exporting GPIOs to a virtual machine, as the VM
> can just grab the full GPIO controller, and no longer needs to care
> about which GPIOs to grab and which not, reducing the attack surface.
> 
> Recently, other use cases have been discovered[1]:
>   - Describing simple GPIO-operated devices in DT, and using the GPIO
>     Aggregator as a generic GPIO driver for userspace, which is useful
>     for industrial control.
> 
> Changes compared to v4[2]:
>   - Add Reviewed-by, Tested-by,
>   - Fix inconsistent indentation in documentation.

I confirm that the diff between v4 and v5 comprises whitespace only.
Thanks for your time to develop this useful functionality!

-- 
Best Regards
Eugeniu Rosca