RE: [PATCH v3 0/6] firmware: arm_scmi: Add SCMI v3.2 pincontrol protocol basic support

[Peng Fan <peng.fan@xxxxxxx>]

> Subject: Re: [PATCH v3 0/6] firmware: arm_scmi: Add SCMI v3.2 pincontrol
> protocol basic support
> 
> On Thu, Feb 01, 2024 at 07:14:17AM +0000, Peng Fan wrote:
> > > Subject: Re: [PATCH v3 0/6] firmware: arm_scmi: Add SCMI v3.2
> > > pincontrol protocol basic support
> > >
> 
> Hi Peng,
> 
> > > On Mon, Jan 29, 2024 at 1:37 PM Peng Fan <peng.fan@xxxxxxxxxxx>
> wrote:
> > >
> > > > And for i.MX95 OEM extenstion, do you have any suggestions?
> > > > I have two points:
> > > > 1. use vendor compatible. This would also benefit when supporting
> > > > vendor protocol.
> > > > 2. Introduce a property saying supporting-generic-pinconf
> > > >
> > > > How do you think?
> > >
> > > While I don't know how OEM extensions to SCMI were designed, the pin
> > > control subsystem has the philosophy that extensions are for minor
> > > fringe stuff, such as a pin config option that no other silicon is
> > > using and thus have no use for anyone else. Well that is actually
> > > all the custom extensions we have.
> > > (This notion is even carried over to SCMI pinctrl.)
> > >
> > > The i.MX95 OEM extension is really odd to me, it looks like a
> > > reimplementation of the core aspects of SCMI pin control, and looks
> > > much more like the old i.MX drivers than like the SCMI driver.
> >
> > i.MX SCMI pin protocol conf settings follows non-SCMI pin conf settings.
> >
> 
> It is not just a matter of using custom SCMI OEM types, it is the whole
> layout/definitions of the i.MX pin/groups/funcs DT bindings that deviates
> from the generic DT bindings layout as handled and expected by the Linux
> Pinctrl subsystem (AFAIU), while the SCMI Pinctrl driver as it stands in this
> series, was conceived, designed and implemented originally by Oleksii to just
> use the generic existing Pinctrl DT bindings; as a consequence, in your i.MX
> extensions, you had to add a dedicated i.MX DT parser to interpret the
> protocol@19 DT snippet in a completely different way, to try to stick your
> custom solution on top of the generic one.

The two links shows the drop of i.MX generic pinconf
https://patchwork.ozlabs.org/project/linux-gpio/patch/1541149669-10857-7-git-send-email-aisheng.dong@xxxxxxx/
https://lore.kernel.org/all/20230302072132.1051590-1-linux@xxxxxxxxxxxxxxxxxx/

For non-scmi platforms, the generic pinconf was supported
for i.MX7ULP for a while, and then dropped in the end per i.MX maintainers
and agreed by Linus.

For i.MX95 SCMI platforms, the firmware design is simple and use similar
programming model to simplify firmware design.

Using generic pinconf means the firmware needs exporting groups/functions/pins
and etc, the firmware design will be complicated and code size enlarged.

I have no better ideas without introducing a compatible for dt map hook.

Build exclusive is not acceptable for distro support.

So the last options is i.MX95 switch back to VENDOR protocol ID saying
0x82. But this means to exports functions of pinctrl-scmi.c and reused
by pinctrl-scmi-imx.c.  If you agree, I will ask firmware developer
switch back to a new SCMI ID, and I will use new ID for i.mx pinctrl
driver.

But in the end I would think when more SCMI vendor protocols
comes in, saying vendor A and vendor B both use ID 0x81,
both use 0x81 as RTC functions, same issue will come back.

Thanks,
Peng.

> 
> Thanks,
> Cristian
> 
> > >
> > > But I sure cannot speak of what is allowed in SCMI OEM extensions or not.
> >
> > + SPEC owner, Souvik. Any comments?
> >
> > Thanks,
> > Peng.
> >
> > >
> > > Yours,
> > > Linus Walleij