On 06/15/2012 01:34 PM, Saugata Das wrote:
On 15 June 2012 16:56, Ulf Hansson<ulf.hansson@xxxxxxxxxxxxxx> wrote:
Hi Saugata,
snip.
The problem in sending CMD0 without power OFF notify is possibility of
some data loss in MMC-4.5 devices.
I don't see the problem here. You will be sending power OFF notify when
you
can. The only difference is when you "wake" the device from sleep mode.
Instead of using CMD5, which may work is some cases and in some cases
not
(without restoring ios). So using CMD0 as common way of waking up from
suspend should be fine. Unless I missed something of course. :-)
CMD0 is a reset. I expect with power OFF notify enable, the eMMC
device will postpone some control information update to its internal
non-volatile memory (e.g. some data structures which are kept in the
controller buffers and not stored in NAND). If we do a CMD0, then the
eMMC device will be reset and we may lose some data. In addition to
that, doing complete card initialization will increase the wakeup time
(for 4.4 devices).
When doing poweroff_notify at suspend you have _always_ cut both vcc and
vccq, according to MMC_CAP2_POWER_OFF_VCCQ_DURING_SUSPEND, which means you
must always use CMD0 to wake up. There is no present internal cache in the
eMMC here.
In sleep mode, you can use CMD5, but until the poweroff notify patches (the
patch that broke suspend/resume, not this one), we have used CMD0 to wake
up. Let's go back to that solution. Then we can address you concern about
"data loss" for sleep mode in separate patch.
Yes, you will get back to the same code flow with the introduction of
the MMC_CAP2_NO_INIT_ON_RESUME. If some host drivers are capable of
executing the CMD5 resume then they enable this cap and go on the
optimized path. The rest go on CMD0 path.
Please do that as a separate patch so we can get this merged asap.
Moreover, I think we should try to prevent from adding another cap for this.
There are another option for a host driver tell whether CMD0 shall be
used or not, by using the regulator supplies. See a patch by Guennadi
Liakhovetski in: http://article.gmane.org/gmane.linux.kernel.mmc/14635,
still being discussed though.
The MMC_CAP2_POWER_OFF_VCCQ_DURING_SUSPEND, can likely soon be removed
as well, when above patch is accepted and host driver is starting to use
the new API.
Kind regards
Ulf Hansson
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