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 17:58, Ulf Hansson wrote:
> On 4 April 2013 14:00, Adrian Hunter <adrian.hunter@intel.com> wrote:
>> On 04/04/13 14:52, Ulf Hansson wrote:
>>> On 4 April 2013 13:44, Adrian Hunter <adrian.hunter@intel.com> wrote:
>>>> 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?)
>>>
>>> Not sure what you mean here. What has a booloader to do with this?
>>
>> When do you think hw reset is used?
> 
> Two types is being used.
> 
> 1. At the mmc_rescan sequence. At this point mmc_do_hw_reset is _not_
> used. Instead mmc_hw_reset_for_init, which onlcy makes use of
> host->ops->hw_reset, no "power_restore" of course. So this has no
> issues whatsoever with this patch.
> 
> 2. At blk request errors, which I thought we were discussing from the
> beginning. In this case mmc_do_hw_reset is used. And it here my
> proposals doing bus_ops->suspend|resume make sense.
> 
> 
>>
>>>
>>>>
>>>> Note that according to spec. CMD0 anyway clears the cache so you have lost
>>>> your data anyway.
>>>
>>> What I am saying that we can try send "cache ctrl" and "power off
>>> notify" before we send CMD0 / do hw reset. The no data shall be lost.
>>
>> With an uninitialized bus?  Or an unresponsive card?
> 
> See above.
> 
> The bus is never uninitialized.
> 
> The card has responded with an error, but that does not have to mean
> that it is completely "unresponsive".

True.  Arguably caching should be disabled at the first sign of trouble
and never re-enabled.

However reset could attempt to flush the cache.  Then, even if the reset is
successful, an error must still be returned if the flush failed.