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

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 24-09-15 12:29, Ian Campbell wrote:
> On Thu, 2015-09-24 at 12:01 +0200, Hans de Goede wrote:
>> 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,
>
> But the being changed here does handle that (the else hz > 50000000 case)
> and that is changing even if we somehow coincidentally arrange that this
> code is never used today I think it is worth mentioning so that if it does
> become used we have the history of when/why it was changed.

Ok, I'll amend the commit message.

>>   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.
>
> Are these timings used for sdio as well then? That seems worth noting.

Yes, but we never use sdio in u-boot, more in general mmc/sdio is
usually used referred to as just mmc (see e.g. the subsystem name, etc.).


>>> 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.
>
> Great.
>
>> 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
>>

Regards,

Hans