linux-kernel - Re: [RFC v1 0/2] Introducing generic SCMI pinctrl driver implementation

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Date:   Tue, 11 Apr 2023 14:27:53 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Oleksii Moisieiev <Oleksii_Moisieiev@...m.com>
Cc:     "sudeep.holla@....com" <sudeep.holla@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>
Subject: Re: [RFC v1 0/2] Introducing generic SCMI pinctrl driver implementation

Hi Oleksii,

thanks for your patches!

On Fri, Apr 7, 2023 at 12:18 PM Oleksii Moisieiev
<Oleksii_Moisieiev@...m.com> wrote:

> This RFC patch series is intended to introduce the potential generic driver for
> pin controls over SCMI protocol, provided in the latest beta version of DEN0056 [0].
>
> On ARM-based systems, a separate Cortex-M based System Control Processor (SCP)
> provides control on pins, as well as with power, clocks, reset controllers. In this case,
> kernel should use one of the possible transports, described in [0] to access SCP and
> control clocks/power-domains etc. This driver is using SMC transport to communicate with SCP via
> SCMI protocol and access to the Pin Control Subsystem.
>
> The provided driver consists of 2 parts:
>  - firmware/arm_scmi/pinctrl.c - the SCMI pinctrl protocol inmplementation
>    responsible for the communication with SCP firmware.
>
>  - drivers/pinctrl/pinctrl-scmi.c - pinctrl driver, which is using pinctrl
>   protocol implementation to access all necessary data.

TBH this looks so good that I am happy to merge it once you send a non-RFC
version.

My main concern would have been the protocol itself, but that was very
carefully tailored to match what the pin control subsystem needs and
I am quite happy with it the way it came out: using strings for groups and
functions.

The scmi code in patch 1 adds an extra layer of abstraction and a vtable
that would not have been necessary if all of the code was confined in
one file in drivers/pinctrl but it is not up to me how the SCMI people
want to abstract their stuff and there seems to be precedents to do things
this way.

I heard that someone wanted to also implement GPIO over SCMI, but
it is not part of this driver so I guess that will be a future addition.
It's a good starting point to add GPIO later.

Yours,
Linus Walleij