Re: [RFC/RFT] MMC: CORE: eMMC in Sleep mode before suspend

["T Krishnamoorthy, Balaji" <balajitk@ti.com>]

On Fri, Jul 22, 2011 at 1:42 AM, Adrian Hunter <adrian.hunter@intel.com> wrote:
> On 19/07/2011 7:48 p.m., Chris Ball wrote:
>>
>> Hi,
>>
>> On Tue, Jul 19 2011, S, Venkatraman wrote:
>>>
>>> On Wed, Jul 13, 2011 at 8:06 PM, Balaji T K<balajitk@ti.com>  wrote:
>>>>
>>>> Put MMC to sleep if it supports SLEEP/AWAKE (CMD5)
>>>> in the mmc suspend to minimize power consumption.
>>>>
>>>> Signed-off-by: Balaji T K<balajitk@ti.com>
>>>
>>> Balaji,
>>>   Would you mind reposting the patch without the RFC and s/CORE/core
>>> in subject line ?
>>> You can add my
>>> Acked-by: Venkatraman S<svenkatr@ti.com>
>>
>> No need to resend, thanks -- pushed to mmc-next with these changes and
>> the ACK.
>>
>> Anyone object to letting this soak in mmc-next for a release and merging
>> it in 3.2?  I'm worried that we'll find card or host quirks around this,
>> and the 3.0 release is probably happening today.
>
> eMMC often have VccQ (logic) always on (or sharing the same power as SDRAM
> which comes to the same thing), but can switch off Vcc (NAND core).
>  However, turning off Vcc without first putting the card to sleep can result
> in errors i.e. you are not allowed to do it.
>
> This patch seems to be covering the "VccQ always on" case but relies on CMD0
> to wake up the card.
>
> If that is what is going on, then some comments to that effect are needed,
> including within mmc_init_card to note that mmc_go_idle is needed for cards
> that are asleep - if that is, in fact, correct.

Yes, current implementation depends on CMD0 in mmc_init_card to wakeup.
Specification allows eMMC card in sleep to respond to CMD0/CMD5
Will send an updated patch with comments added.

>
> Also, wouldn't it be nice to wake up the card with CMD5 which should be much
> faster than re-initialising?
>
>> - Chris.
>
>