linux-kernel - Re: [PATCH v2 1/8] dt-bindings: pinctrl: Add thead,th1520-pinctrl bindings

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Date: Fri, 17 May 2024 07:48:17 -0500
From: Emil Renner Berthing <emil.renner.berthing@...onical.com>
To: Rob Herring <robh@...nel.org>, 
	Emil Renner Berthing <emil.renner.berthing@...onical.com>
Cc: linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-riscv@...ts.infradead.org, 
	Linus Walleij <linus.walleij@...aro.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	Jisheng Zhang <jszhang@...nel.org>, Guo Ren <guoren@...nel.org>, Fu Wei <wefu@...hat.com>, 
	Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, 
	Drew Fustini <dfustini@...libre.com>
Subject: Re: [PATCH v2 1/8] dt-bindings: pinctrl: Add thead,th1520-pinctrl bindings

Rob Herring wrote:
> On Wed, Jan 03, 2024 at 02:28:38PM +0100, Emil Renner Berthing wrote:
> > Add bindings for the pin controllers on the T-Head TH1520 RISC-V SoC.
> >
> > Signed-off-by: Emil Renner Berthing <emil.renner.berthing@...onical.com>
> > ---
> >  .../pinctrl/thead,th1520-pinctrl.yaml         | 372 ++++++++++++++++++
> >  1 file changed, 372 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/pinctrl/thead,th1520-pinctrl.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/pinctrl/thead,th1520-pinctrl.yaml b/Documentation/devicetree/bindings/pinctrl/thead,th1520-pinctrl.yaml
> > new file mode 100644
> > index 000000000000..d3ad7a7cfdd1
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/pinctrl/thead,th1520-pinctrl.yaml
> > @@ -0,0 +1,372 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/pinctrl/thead,th1520-pinctrl.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: T-Head TH1520 SoC pin controller
> > +
> > +maintainers:
> > +  - Emil Renner Berthing <emil.renner.berthing@...onical.com>
> > +
> > +description: |
> > +  Pinmux and pinconf controller in the T-Head TH1520 RISC-V SoC.
> > +
> > +  The TH1520 has 3 groups of pads each controlled from different memory ranges.
> > +  Confusingly the memory ranges are named
> > +    PADCTRL_AOSYS  -> PAD Group 1
> > +    PADCTRL1_APSYS -> PAD Group 2
> > +    PADCTRL0_APSYS -> PAD Group 3
> > +
> > +  Each pad can be muxed individually to up to 6 different functions. For most
> > +  pads only a few of those 6 configurations are valid though, and a few pads in
> > +  group 1 does not support muxing at all.
> > +
> > +  Pinconf is fairly regular except for a few pads in group 1 that either can't
> > +  be configured or has some special functions. The rest have configurable drive
> > +  strength, input enable, schmitt trigger, slew rate, pull-up and pull-down in
> > +  addition to a special strong pull up.
> > +
> > +  Certain pads in group 1 can be muxed to AUDIO_PA0 - AUDIO_PA30 functions and
> > +  are then meant to be used by the audio co-processor. Each such pad can then
> > +  be further muxed to either audio GPIO or one of 4 functions such as UART, I2C
> > +  and I2S. If the audio pad is muxed to one of the 4 functions then pinconf is
> > +  also configured in different registers. All of this is done from a different
> > +  AUDIO_IOCTRL memory range and is left to the audio co-processor for now.
>
> It is still not clear to me if each instance is a different programming
> model or the same with just different connections. The latter should
> be the same compatible string. That needs to be answered in *this*
> patch, not a reply.

Hi Rob,

Sorry for the late response. I honestly don't know exactly what you mean by
differenty programming models and what the difference is, so I'll need a bit of
help with what you want me to write here.

Any driver for the TH1520 SoC (not just Linux) would need some way to discern
between the 3 pin controllers so they know how many pins to control and what
pinmux settings are valid. Basically they'd need the data in the three
th1520_group{1,2,3}_pins arrays in the driver and a way to know which of them
to use.

https://lore.kernel.org/linux-riscv/20240103132852.298964-3-emil.renner.berthing@canonical.com/

Another solution would be to just have one compatible value, and then let the
driver figure out which of the 3 pin controllers it's probing from the base
physical memory address. That would work fine.

A third solution would be to encode the data in those three arrays into the
device tree, but I thought we didn't want to encode register information in
device trees.

/Emil