Re: [PATCH 2/2] mmc: sunxi: Also set SDXC_LOW_POWER_ON

[Ulf Hansson]

On 25 May 2015 at 09:02, Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
> Hi,
>
> On 24-05-15 20:04, Michal Suchanek wrote:
>>
>> The function sunxi_mmc_oclk_onoff filters out the SDXC_LOW_POWER_ON flag
>> but never sets it.
>>
>> Set SDXC_LOW_POWER_ON when oclk is disabled.
>
>
> Nack, looking at the datasheet I do not thing this patch actually
> does anything, according to the datasheet setting this bit to 1 results
> in: "Turn off card clock when FSM in IDLE state", iow this does mmc clock
> gating on idle automatically in hardware, since we completely disable the
> clock on clock-off by clearing SDXC_CARD_CLOCK_ON setting this bit on
> clock-off is a nop.
>
> We could consider actually setting this to safe power when setting the clock
> on, for doing that it would be good to look at the android code and see if
> it ever sets this bit and if so when.
>
> WRT CONFIG_MMC_CLKGATE we are probably better off using SDXC_LOW_POWER_ON
> then that when it is enabled. So maybe we should set SDXC_LOW_POWER_ON
> based on #ifdef WRT CONFIG_MMC_CLKGATE, and have some way to tell the
> mmc core to not do clock gating on this host ?

I am planning to remove the entire thing for CONFIG_MMC_CLKGATE, maybe
it's time to do that now!?

Most hosts use runtime PM to deal with clock gating at idle and
browsing def configs tells me that CONFIG_MMC_CLKGATE isn't much used.

Kind regards
Uffe
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