linux-kernel - Re: [PATCH v1 1/8] dt-bindings: pinctrl: Add thead,th1520-pinctrl bindings

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Date: Thu, 21 Dec 2023 04:21:34 -0800
From: Emil Renner Berthing <emil.renner.berthing@...onical.com>
To: Linus Walleij <linus.walleij@...aro.org>, Jisheng Zhang <jszhang@...nel.org>, 
	Guo Ren <guoren@...nel.org>, Drew Fustini <dfustini@...libre.com>, 
	Emil Renner Berthing <emil.renner.berthing@...onical.com>
Cc: linux-gpio@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org, 
	Hoan Tran <hoan@...amperecomputing.com>, Serge Semin <fancer.lancer@...il.com>, 
	Bartosz Golaszewski <brgl@...ev.pl>, Andy Shevchenko <andy@...nel.org>, Rob Herring <robh+dt@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	Fu Wei <wefu@...hat.com>, Paul Walmsley <paul.walmsley@...ive.com>, 
	Palmer Dabbelt <palmer@...belt.com>
Subject: Re: [PATCH v1 1/8] dt-bindings: pinctrl: Add thead,th1520-pinctrl bindings

Linus Walleij wrote:
> Hi Emil,
>
> thanks for your patch!
>
> On Fri, Dec 15, 2023 at 3:39 PM Emil Renner Berthing
> <emil.renner.berthing@...onical.com> wrote:
>
> > +  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
>
> Really, even in the documentation? If you look at the layout on the actual
> chip, does a pattern emerge?

Yes, the documentation is where I got this from:
https://git.beagleboard.org/beaglev-ahead/beaglev-ahead/-/blob/main/docs/TH1520%20System%20User%20Manual.pdf

The pinmux chapter starting on page 31 only talks about the 3 pad groups, but
if you match the base addresses, table 3-8 page 46, with the memory map, table
1-2 page 1, they same base addresses have the PADCTRL names above.

> I think some use the north/south/east/west as group names with the BGA
> chip facing up with the package text correctly readable then it is a bit
> like a map.

I don't know if or where such documentation is available.
Jisheng, Guo or Drew, do you know?

> > +          function:
> > +            $ref: /schemas/types.yaml#/definitions/string
> > +            enum: [ "0", "1", "2", "3", "4", "5" ]
> > +            description: The mux function to select for the given pins.
>
> So why is the opaque names "0", "1" etc used, and they will be the same for
> all pins I bet. Most drivers use a string identifying the actual function here.
> Such as "i2c", "gpio", etc.
>
> Names that are just figures are *impossible* to understand without access
> to a datasheet.
>
> The point of device trees sources are to be human readable, strings of
> magic numbers are not human readable at all.
>
> > +          bias-disable: true
> > +
> > +          bias-pull-up:
> > +            type: boolean
> > +
> > +          bias-pull-down:
> > +            type: boolean
> > +
> > +          drive-strength:
> > +            enum: [ 1, 2, 3, 5, 7, 8, 10, 12, 13, 15, 16, 18, 20, 21, 23, 25 ]
>
> milliamperes? Then use drive-strength-microamp.
>
> If not, explain what each setting means, i.e. the number of max microamps.

It *is* the number of mA. I can change it uA if that's better.

> At which point using drive-strength-microamp and a translation table in the
> driver may be a better idea.

That's what it does, just with mA.

> The only reason to use opaque numbers is if 1, 2 (etc) mean something like
> "number of driver stages" with a current output that varies with technology.
>
> > +          thead,strong-pull-up:
> > +            oneOf:
> > +              - type: boolean
> > +              - $ref: /schemas/types.yaml#/definitions/uint32
> > +                enum: [ 0, 2100 ]
> > +            description: Enable or disable strong 2.1kOhm pull-up.
>
> Just use bias-pull-up with an argument.
>
> bias-pull-up = <2100000>;
>
> No argument would be the default setting.
>
> No need for custom bindings.
>
> > +        uart0_pins: uart0-0 {
> > +            tx-pins {
> > +                pins = "UART0_TXD";
>
> Pins have reasonable names, but...
>
> > +                function = "0";
>
> What about function = "uart_0" hmmm?
>
> Yours,
> Linus Walleij
>
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