Re: [PATCH v2 4/4] ARM: dts: mt8135: Add pinctrl node for mt8135.

On Thu, Oct 02, 2014 at 04:02:58PM +0200, Linus Walleij wrote:

On Wed, Sep 24, 2014 at 2:40 PM, Sascha Hauer [off-list ref] wrote:

quoted

On Wed, Sep 24, 2014 at 01:23:09PM +0200, Linus Walleij wrote:

quoted

quoted

I haven't got to reviewing the driver, but this looks just wrong.

Have the magic numbers in the driver.

Use strings to describe functions, not integers.

Interrupts, clocks, gpios, dma channels, nearly everything in the device tree is
arbitrarily numbered. Instead of "irq-i2c0" we have <0 36 IRQ_TYPE_LEVEL_HIGH>
in the device tree. These numbers can be resolved efficiently in the
driver by shifting them to get a bitmask or by adding them as offset to
a register base.
Why do you want to make pinctrl different?

Because pin control is about combining groups of pins with
certain functions.

quoted

Thanks to the recently
introduced defines in the device trees these numbers are not magic at
all anymore.

Yeah that is good but not what I'm after here.

quoted

quoted

We need to move toward standardized device tree bindings
for this stuff, and that means using strings, not magic
numbers.

Agreed for standardized device tree bindings, but not for using strings.

What is the alternative? Device Tree is very much about strings,
as is shown by the pin config bindings.

The alternative is to use numbers. The majority of SoCs have a bit field
per pad which is used for muxing the pad to different functions. The
natural way to describe this is a pair of numbers: <pad-number>
<function-number>.  The pad number can normally be directly translated
into a register offset and the function number to a value written to
that register. This is true for most SoCs I know of and makes it very
easy to generate code for and to prove for correctness of both the code
and the device tree.

Sascha

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