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

[Arend van Spriel <arend@broadcom.com>]

On 01/13/15 15:56, Ulf Hansson wrote:
> [...]
>
>>>> 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?

It is read from the Capabilities register in the SD host controller, ie. 
in field "Timer Count for Re-Tuning" (see below).

Regards,
Arend

Timer Count for Re-Tuning
This field indicates an initial value of the Re-Tuning Timer for 
Re-Tuning Mode 1 to 3. Setting to 0 disables Re-Tuning Timer.
0h	Re-Tuning Timer disabled
1h	1 seconds
2h	2 seconds
3h	4 seconds
4h	8 seconds
.....	......................
n	2(n-1) seconds
.....	......................
Bh	1024 seconds
Eh - Ch	Reserved
Fh	Get information from other source

>>
>>>
>>> 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