Re: [PATCH 1/1] ARM: Exynos: Add generic compatible string

[Sachin Kamat <sachin.kamat@linaro.org>]

On 20 February 2014 23:18, Arnd Bergmann <arnd@arndb.de> wrote:
> On Thursday 20 February 2014 18:34:23 Tomasz Figa wrote:
>> On 20.02.2014 18:00, Arnd Bergmann wrote:
>> >> Of course nothing stops you from retaining more specific compatible
>> >> strings. In fact, this is probably the most appropriate solution,
>> >> because in future you might find out that certain SoCs need some special
>> >> differentiation, e.g. same ID value on two SoCs.
>> >>
>> >> So, to apply this to our case, our Exynos 5250 based Arndale board would
>> >> be changed from
>> >>
>> >> compatible = "insignal,arndale", "samsung,exynos5260";
>> >>
>> >> to
>> >>
>> >> compatible = "insignal,arndale", "samsung,exynos5260", "samsung,exynos";
>> >
>> > Right, this would make sense.
>> >
>> >> Now, the board file will be able to match simply by "samsung,exynos"
>> >> compatible string and SoC-specific code in mach-exynos (hopefully none
>> >> after it gets cleaned up fully) will use soc_is_exynos*() macros (what
>> >> AFAIK it is already doing at the moment).
>> >
>> > On principle, I would not take things out of the match list, if that
>> > would break booting with old DT file that don't list "samsung,exynos"
>> > as compatible. But for new SoCs that would work.
>>
>> My proposal was about simply adding a fully generic string, without
>> removing the specific ones. For already supported SoCs this is pretty
>> obvious, as existing DTBs would not have this generic string listed. But
>> the specific strings should be also present in DTSes of new SoCs, even
>> if not recognized by the kernel, to make sure that in future any
>> SoC-specific quirks could be easily handled.
>
> Yes, that's ideal.
>
>> > Using soc_is_exynos*() too much of course also isn't good. A lot of
>> > the things tested for should probably be checked from individual DT
>> > properties, but again we have to find the right balance. I wouldn't
>> > mind getting rid of the soc_is_exynos*() macros completely, because
>> > a) we can't use them in device drivers
>> > b) all platform code is supposed to be in drivers
>> > c) both rules are enforced for arm64
>>
>> I fully agree. As I said, after cleaning up mach-exynos/ there should be
>> no more code left using soc_is_*() macros. Ideally, the whole
>> mach-exynos/ should collapse into a single, trivial file, with
>> everything done in dedicated drivers.
>
> Right.

Now that we have a broader agreement on this, I think we can go ahead with the
following steps as an initial approach:
1. Have a common machine file for both exynos4 and 5 files, mach-exynos-dt.c.
2. Introduce a generic compatible string "samsung,exynos".
3. Append this to the compatible property list for existing boards.

If this plan looks OK, I can send across patches doing this.

-- 
With warm regards,
Sachin