[U-Boot] [PATCH] sunxi: mmc: Fix clk-delay settings

[Hans de Goede]

Hi,

On 24-09-15 11:40, Ian Campbell wrote:
> On Wed, 2015-09-23 at 21:59 +0200, Hans de Goede wrote:
>> In recent allwinner kernel sources the mmc clk-delay settings have been
>> slightly tweaked, and for sun9i they are completely different then what
>> we are using.
>>
>> This commit brings us in sync with what allwinner does, fixing problems
>> accessing sdcards on some A33 devices (and likely others).
>>
>> For pre sun9i hardware this makes the following changes:
>> -At 400Khz change the sample delay from 7 to 0 (first introduced in A31 sdk)
>
> This one applied to sun9i as well as pre I think?
>
>> -At 50 Mhz change the sample delay from 5 to 4 (first introduced in A23 sdk)
>
> By my reading it also changes oclk from 2 to 1 on <sun9i @ >50MHz.

Right, I did not list that as we never do > 50MHz, later on in the code
we've:

	cfg->f_max = 52000000;

And that 52 is somewhat symbolically there, it is meant for 52MHz sdio
where as mmc / sdcards run at 50MHz max.

> I don't really follow the a/w SDK stuff, is it the case that a given Ann
> SDK is tested and supported by Allwinner and used on real devices for
> processors Amm < Ann (chronologically, ?

Yes and no, Allwinner used to have separate kernel sources for each
die, so one for sun4i, sun5i, sun6i and sun7i.

Recently they have changed to one unified kernel tree though, so all
of sun6i, sun8i and sun9i build from the same kernel tree. Note that
sun7i is missing from the list.

> IOW if a change was introduced in the A31 SDK do we then have confidence
> that it doesn't break A20 due to Allwinners (and their customer's) use of
> the A31 SDK on A20 or are we relying on our own + community testing?

It is safe to assume that the A23 changes do not break on the A31 since
that is using the same kernel sources. The changes may cause issues
on A20 though (A10 / A13 do not use the sample delay bits of the register
AFAICT). So I've run several tests on A20 and things seem to work fine
with the new settings there.

I believe that the mmc controller and the mmc clock bits really are the
same over all of A20 / A23 / A31 / A33, and that these new tweaked values
are better to use everywhere.

Regards,

Hans