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

[Linus Walleij <linus.walleij@linaro.org>]

Hi Emil,

thanks for your patch!

On Fri, Dec 15, 2023 at 3:39 PM Emil Renner Berthing
<emil.renner.berthing@canonical.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?

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.

> +          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.

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

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