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

[Adrian Hunter <adrian.hunter@intel.com>]

On 13/04/15 15:30, Ulf Hansson wrote:
> On 2 April 2015 at 18:18, Adrian Hunter <adrian.hunter@intel.com> wrote:
>> On 2/04/2015 4:05 p.m., Ulf Hansson wrote:
>>>
>>> [...]
>>>
>>>>>
>>>>>>    - ability to enable / disable re-tuning
>>>>>
>>>>>
>>>>> Handled internally by the mmc core.
>>>>
>>>>
>>>> The host controller driver enables re-tuning based on whether the host
>>>> controller requires it for that transfer mode. For example, only the
>>>> SDHCI
>>>> host controller knows if tuning is required for SDR50 mode according to
>>>> the
>>>> SDHCI capability register bit 45.
>>>
>>>
>>> That seems a bit silly.
>>>
>>> All hosts wants the re-tuning to be "enabled" if the current used
>>> speed mode requires it. It's not a host driver thing to deal with,
>>> just the core.
>>
>>
>> No it is up to the host controller. That is how it is in the
>> SD Host Controller Specification. Both whether to tune SDR50 and
>> whether to run a re-tuning timer.
>>
>> Tuning is inherently a host controller problem. The card can always
>> receive correctly from the host, but the host has to adjust its
>> "sampling point" to receive from the card. Only the host knows its
>> capabilities in this regard.
> 
> The requirement of doing re-tuning is stated in the eMMC/SD specs. The
> SDHCI spec is just adopting to what these specs already states. Then,
> I think the mmc core is the only one, who shall be able of
> enable/disable re-tuning and thus we shouldn't need any APIs for that.
> 
> Hosts needs to be able to flag that re-tuning is needed and to
> configure the re-tuning timeout (optional).

OK sent patch set V5