Platform setup via DTS

[Joel Stanley]

Hey Anton,

On Thu, Aug 11, 2016 at 9:27 PM, Anton D. Kachalov <mouse at yandex-team.ru> wrote:
> I would like to start a little discussion around board setup process in arch/arm/mach-aspeed/aspeed.c.
> For most cases this process is "flat": just modifying regs one-by-one. Sometimes with applying mask.
> I have an idea to add an array of "instructions" to the Device Tree in the following manner
> (I hope dtc's preprocess via cpp resolve ORed macro in the correct way):

I agree that we need to remove the board file.

However, we will not be able to get changes upstream that use the
device tree as a scripting language :)

I think the solution is to write a driver for the different parts of
the system we require. Andrew J has done that for the multi-function
pin control registers in the SCU. I've got a work in progress driver
for the clock related registers. Next up would be a driver for the LPC
register space to properly configure that.

Cheers,

Joel

>
> ==========
> #include <dt-bindings/soc/aspeed.h>
>
> / {
>     model = "Our HW";
>     compatible = "aspeed,ast2400";
>     board-setup = <WR, AST_BASE_LPC | 0x9c, 0x02010023, 0>,
>                            <WR, AST_BASE_SCU, SCU_PASSWORD, 0>,
>                            <WR, AST_BASE_SCU | 0x80, 0xcb000000, 0>,
>                            ...
>                             /* write(read() | 0x1000) */
>                            <OR, AST_BASE_SCU | 0x2c, 0x00001000, 0>,
>
>                            /* write((read() &~ 0x2000) | 0x1000) */
>                            <OR, AST_BASE_SCU | 0x2c, 0x00001000, 0x2000>;
> ==========
>
> or in less talkative way:
>
> ==========
>                             /* write((read() &~ 0) | 0xcb000000) */
>                            <AST_BASE_SCU | 0x80, 0xcb000000, 0>,
>                            ...
>                             /* write((read() &~ 0x1000) | 0x1000) */
>                            <AST_BASE_SCU | 0x2c, 0x00001000, 0x1000>,
> ==========
>
> to completely eliminate board-specific init functions.
>
>
> --
> Anton D. Kachalov
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