linux-kernel - Re: [PATCH V2 1/3] firmware: zynqmp: Add MMIO read and write support for PS

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Date:   Wed, 11 Aug 2021 15:46:23 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Piyush Mehta <piyush.mehta@...inx.com>,
        Arnd Bergmann <arnd@...db.de>, Zou Wei <zou_wei@...wei.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Michal Simek <michal.simek@...inx.com>, wendy.liang@...inx.com,
        Nobuhiro Iwamatsu <iwamatsu@...auri.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Rajan Vaja <rajan.vaja@...inx.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, git <git@...inx.com>,
        Srinivas Goud <sgoud@...inx.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 1/3] firmware: zynqmp: Add MMIO read and write support
 for PS_MODE pin

On Wed, Aug 11, 2021 at 3:08 PM Linus Walleij <linus.walleij@...aro.org> wrote:
>
> On Thu, Aug 5, 2021 at 7:42 PM Piyush Mehta <piyush.mehta@...inx.com> wrote:
>
> > Add Xilinx ZynqMP firmware MMIO APIs support to set and get PS_MODE
> > pins value and status. These APIs create an interface path between
> > mode pin controller driver and low-level API to access GPIO pins.
> >
> > Signed-off-by: Piyush Mehta <piyush.mehta@...inx.com>
> > ---
> > Changes in v2:
> > - Added Xilinx ZynqMP firmware MMIO API support to set and get pin
> >   value and status.
>
> I doubt this is "GPIO".
> General Purpose? I think not. It seems to be about boot mode.

Agreed.

> If you need a userspace ABI, then add sysfs files to this firmware
> driver instead of bridging it to the GPIO subsystem.

I don't really want custom user interfaces in firmware drivers either.

What is the high-level description of the 'PS_MODE' here? Is
this perhaps something we already have a user interface for?

       Arnd