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

Ulf Hansson
2015-01-13T15:41:58Z

On 13 January 2015 at 16:11, Arend van Spriel <arend@broadcom.com> wrote:
> 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

Thanks for sharing this information, but unfortunate I don't
understand much from it.

Is the host driver intended to read/poll this register to find a good value?

Isn't heat one of the most important factor that could effect the need
for a re-tune? Does then the controller internally dynamically update
this register (since it keep track of heat or similar)?

Kind regards
Uffe