Re: [PATCH 1/3] mmc: core: Remove power_restore bus_ops for mmc and sd

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

On 04/04/13 12:55, Ulf Hansson wrote:
> On 4 April 2013 10:46, Adrian Hunter <adrian.hunter@intel.com> wrote:
>> On 01/03/13 14:47, Ulf Hansson wrote:
>>> From: Ulf Hansson <ulf.hansson@linaro.org>
>>>
>>> The mmc_power_restore|save_host API is only used by SDIO func drivers. SDIO
>>
>> NAK - it is also used by eMMC hardware reset i.e. mmc_do_hw_reset()
> 
> True for eMMC, but for SD card the bus_ops can go away. Thanks for
> spotting this Adrian!
> 
> Although, I see some serious problems with the mmc_do_hw_reset
> function - it could cause eMMC data corruption.
> 
> Issuing hw reset and doing re-initialization by using the mmc
> bus_ops->power_restore will mean no consideration is taken to "cache
> ctrl", "bkops" and "power off notify". I think it must.
> 
> So the more proper way instead of calling power_restore, should be to
> use bus_ops->suspend and bus_ops->resume callbacks from the
> mmc_do_hw_reset function. Additionally if bus_ops->suspend is done
> successfully, we should be able to skip the actual hw reset and just
> do bus_ops->resume.
> 
> Do you have any thoughts on this?

Certainly the bootloader should leave the eMMC is a safe state including:
flushing the cache or turning it off (why did it turn on?), stopping
background operations (why did it start them?), disabling power-off
notification CMD0? (again why it it enable it?)

Note that according to spec. CMD0 anyway clears the cache so you have lost
your data anyway.