Re: [PATCH V4 01/15] mmc: host: Add facility to support re-tuning

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

On 04/02/15 14:25, Ulf Hansson wrote:
> On 2 April 2015 at 14:18, Adrian Hunter<adrian.hunter@intel.com>  wrote:
>> On 02/04/15 15:10, Ulf Hansson wrote:
>>> On 2 April 2015 at 12:30, Arend van Spriel<arend@broadcom.com>  wrote:
>>>> On 04/02/15 10:43, Ulf Hansson wrote:
>>>>>
>>>>> [...]
>>>>>>>>>
>>>>>>>>>      - ability to hold off re-tuning if the card is busy
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> What do you mean by "card is busy"?
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> I guess, more accurately, any time the card is in a state that is
>>>>>>> incapable
>>>>>>> of supporting re-tuning. For example:
>>>>>>>           - DAT0 busy
>>>>>>
>>>>>>
>>>>>>
>>>>>> This state is not specific to re-tuning. An SDIO device can keep DAT0
>>>>>> busy
>>>>>> at which the host controller can not start another request.
>>>>>
>>>>>
>>>>> Not entirely true. Some commands are allowed during this period, for
>>>>> example CMD13 (which doesn't exist for SDIO)
>>>>
>>>>
>>>> Yeah. I was wondering whether to mention that.
>>>>
>>>>> Anyway, I get the point. Thanks!
>>>>>
>>>>>>
>>>>>>>           - between dependent commands like erase start, end, etc
>>>>>>>           - card is asleep
>>>>>>> Also SDIO cards can have a custom sleep state where tuning won't work.
>>>>>>
>>>>>>
>>>>>>
>>>>>> Our SDIO wifi device has such a state and it can only come out of it upon
>>>>>> CMD52 write or CMD14 (ExitSleep).
>>>>>
>>>>>
>>>>> So how will the mmc core know about these states? I guess we will
>>>>> require SDIO func drivers to deal with enable/disable or hold/release
>>>>> of re-tuning then?
>>>>
>>>>
>>>> This is actually why in the past we tried to only kick off retuning before a
>>>> request that requires use of data line(s) so mmc core (or sdhci) would not
>>>> do re-tuning when SDIO func used CMD52 to wakeup the device. I never tried
>>>> CMD14 approach and not even sure from which spec it comes (maybe eMMC).
>>>
>>> That's an interesting idea. It would eliminate the need for SDIO func
>>> drivers to care about holding/releasing re-tuning.
>>>
>>> Would be nice to hear about Adrian's thoughts around this as well.
>>
>> I don't see how it would work because re-tuning is needed after the host
>> controller runtime resumes. i.e. once the SDIO wifi card stops being active
>> the host controller will runtime suspend.
>
> Why do we always need to re-tune from this phase?
>
> What Arend points out is that we could "delay" the re-tune until we
> know there is a DATA request. Wouldn't that work for SDHCI as well?

You beat me to it, but that is indeed what I meant.

Regards,
Arend

>>
>> Also I would expect doing re-tuning before every data request would likely
>> be unacceptable from a performance point of view.
>>
>>>
>>>>
>>>>> I don't like this, but if there is no other way... Also, we must be
>>>>> very careful on which API we exports for SDIO func drivers to use. The
>>>>> can easily be misinterpreted.
>>>>>
>>>>> [...]
>>>
>>> Kind regards
>>> Uffe
>>>
>>>
>>