[linux-sunxi] Re: [PATCH 4/4] simplefb: add clock handling code

[Geert Uytterhoeven]

On Wed, Aug 27, 2014 at 10:55 AM, Maxime Ripard
<maxime.ripard at free-electrons.com> wrote:
>> >> Is simplefb something that should be in the device tree distinctly in
>> >> the first place - shouldn't it be a subset of the functionality of the
>> >> video nodes?  It's the same hardware being driven differently.
>> >
>> > Therorically, yes, but that would mean knowing beforehand what the
>> > final binding will look like, even before submitting the driver. Since
>> > the bindings are always reviewed, and most of the time changed
>> > slightly, that wouldn't work very well with the DT as a stable ABI
>> > policy I guess.
>>
>> If you don't know how the bindings for a device will look like at the time of
>> writing your DTS, you're always screwed, whether you add a simpefb
>> node or not.
>>
>> If you know how the bindings look like, just add the device, with an extra
>> "linux,simplefb" compatibility value.
>> If you don't know how the bindings look like, do your utter best in
>> guessing. Your DTS must be amended later anyway, either because
>> you guessed wrong[*] (in case you added a node to have simplefb
>> working), or because you have to add a real device node (in case you
>> didn't add one for simplefb).
>
> Let's be conservative and consider the case where we would guess
> wrong.
>
> If we just rely on a simplefb node, when reviewing and integrating the
> "new" bindings to describe accureately the various IPs involved in the
> display path, we would obviously create new compatibles for
> them. Since it's new compatibles, we can come up with any binding we'd
> like, without have to consider the backward compatibility, since it's
> a new binding.
>
> Then, we just remove the simplefb, all is good.

I would keep the simplefb compatible value. Else you break compatibility
with old kernels that don't have your new driver.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds