Re: [PATCH 02/13] mmc: host: Add facility to support re-tuning

Ulf Hansson
2015-01-13T14:56:46Z

[...]

>>> Thank you for looking at the patches.
>>>
>>> I am not sure I know what you mean. sdhci already has a re-tuning timer, so
>>> this is just moving it into core, where it won't be used by other drivers
>>> unless they enable it.
>>
>> I am kind of questioning the re-tuning timer in sdhci. What is it good for?
>
> It is part of the SD Host Controller Standard Specification. The timer
> ensures that re-tuning is done before temperature changes could affect the
> "sampling point". It is needed for re-tuning mode 1 for UHS-I modes like SDR104.

Does the spec say what value the timer should have?

>
>>
>> Can sdhci rely on that the mmc core performs a re-tune from the
>> request retry mechanism instead?
>
> Not according to the standard.

We don't have to implement everything that comes with the standard. We
can leave things out.

>
>>
>>>
>>> I am not sure what you want to leave in sdhci.c and what you want in core,
>>> if anything.
>>
>> We need all the infrastructure code in the core. Much like what your
>> patchset does. Except that I would like you to remove the option of
>> having a timer and the corresponding complexity it adds.
>
> If we are going to follow the standard then that doesn't seem to be an option.

I am not suggestion us to violating the spec. I am suggesting to
currently not support all of it.

>
>>
>>>
>>> At a minimum I need sdhci to be able to switch from hs400 to hs200, re-tune,
>>> and switch back.
>>
>> As stated, I am only questioning the timer, nothing else.
>
> Ok so how should I proceed?
>

As I stated, let's try without the timer first.

If we find it's not enough to recover at the request retry path, since
it happens too often - lets deal with that then.

Okay?

Kind regards
Uffe