Re: [PATCH 2/3] MMC: OMAP: HSMMC: add runtime pm support

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On Wed, Jun 29, 2011 at 2:00 AM, Kevin Hilman <khilman@xxxxxx> wrote:
> "T Krishnamoorthy, Balaji" <balajitk@xxxxxx> writes:
>
>> On Tue, Jun 28, 2011 at 10:52 PM, Paul Walmsley <paul@xxxxxxxxx> wrote:
>>> (cc'ing Adrian also)
>>>
>>> Hi Balaji
>>>
>>> On Wed, 22 Jun 2011, Balaji T K wrote:
>>>
>>>> Use runtime autosuspend APIs to enable auto suspend delay
>>>
>>> Does this really need to use runtime autosuspend?  Seems to me that since
>>> PM runtime is just controlling the MMC IP blocks and not the regulators in
>>> this instance, this could simply use pm_runtime_put*() and just avoid the
>>> extra power wastage and complexity involved in autosuspend.
>>>
>>
>> I have seen some instabilities if delay is very less, on some production boards.
>> The previous implementation used 100ms delay before disabling the clocks.
>
> And your new one is using 50ms.  How did this value come about?
>
I don't have any specific affinity to this number, but when requests
are bursty, they arrive
within a few 10s of ms within each other. Didn't want to have the
context/save restore
penalty associated with every request.

> As Paul mentioned, the timeout value here is probably usecase depeend
>

There is no direct relationship to the use case. Block layer buffers
and reworks the order
of requests and they are usually queued together. Having no context
save / restore
penalty for each request is definitely desirable.
(As I understand, MMC can lose context independent of MPU on OMAP4).
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