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Date:   Fri, 20 Oct 2023 09:21:02 +0900
From:   AKASHI Takahiro <takahiro.akashi@linaro.org>
To:     andy.shevchenko@gmail.com
Cc:     sudeep.holla@arm.com, cristian.marussi@arm.com, robh+dt@kernel.org,
        krzysztof.kozlowski+dt@linaro.org, conor+dt@kernel.org,
        linus.walleij@linaro.org, Oleksii_Moisieiev@epam.com,
        linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-gpio@vger.kernel.org
Subject: Re: [RFC v2 0/5] gpio: add pinctrl based generic gpio driver
Message-ID: <ZTHH7vwG7hRneZls@octopus>
Mail-Followup-To: AKASHI Takahiro <takahiro.akashi@linaro.org>,
        andy.shevchenko@gmail.com, sudeep.holla@arm.com,
        cristian.marussi@arm.com, robh+dt@kernel.org,
        krzysztof.kozlowski+dt@linaro.org, conor+dt@kernel.org,
        linus.walleij@linaro.org, Oleksii_Moisieiev@epam.com,
        linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-gpio@vger.kernel.org
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Hi Andy,

On Fri, Oct 20, 2023 at 12:27:58AM +0300, andy.shevchenko@gmail.com wrote:
> Thu, Oct 05, 2023 at 11:58:38AM +0900, AKASHI Takahiro kirjoitti:
> > This is a revised version of my previous RFC[1]. Although I modified
> > the commits to make them look SCMI-independent, they are still posted
> > as RFC because I have never tested them on real hardware.
> > 
> > (background)
> > I'm currently working on implementing SCMI pinctrl/gpio drivers
> > on U-Boot[2]. Although the pinctrl driver for the kernel[3] was submitted
> > by EPAM, it doesn't contain the gpio driver and I believe that we should
> > discuss a couple of points on the kernel side to finalize my design for
> > U-Boot. 
> > 
> > So this RFC is intended for reviews, especially to raise some issues.
> > 
> > 1) how to obtain a value on an input pin
> >    All the existing gpio drivers are set to obtain a value on an input
> >    pin by accessing the hardware directly. In SCMI case, however, this is
> >    just impossible in its nature and must be supported via a protocol
> >    using "Input-value" configuration type. (See the spec[4], table-23.)
> > 
> >    The current pinconf framework is missing the feature (the pinconf
> >    parameter and a helper function). See patch#1, #2 and #3.
> > 
> >    Please note that there is an issue around the pin configuration in
> >    EPAM's current pinctrl driver as I commented[5].
> > 
> > 2) DT bindings
> >    I would like to propose a generic binding for pinctrl based gpio driver.
> >    This allows a "consumer" driver to handle gpio pins like as other
> >    normal gpio controllers support. (patch#5)
> > 
> > 3) generic GPIO driver
> >    Based on (2), I tried to prototype a generic driver in patch#4.
> >    Thanks to a set of existing pinctrl_gpio helper functions, except (1),
> >    It seems that the driver can be implemented not relying on pin controller
> >    specific code, at least for SCMI pinctrl.
> > 
> > I will appreciate any comments.
> 
> Any comment here: I'm listed as a designated reviewer of GPIO patches, why am I
> not Cc'ed on this?

My apologies. I will add you in Cc.

> I definitely have some comments against the code (no DT,
> though). Please, use (up-to-date) MAINTAINERS in your v3.

Please don't hesitate to make comments here on v2 so that I can
include your reviews in v3.

Thanks,
-Takahiro Akashi


> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
>