linux-kernel - Re: [PATCH 2/2] mmc: sunxi: Also set SDXC_LOW_POWER

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Date:	Thu, 28 May 2015 10:02:47 +0200
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Hans de Goede <hdegoede@...hat.com>
Cc:	Michal Suchanek <hramrach@...il.com>, linux-sunxi@...glegroups.com,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	David Lanzendörfer <david.lanzendoerfer@....ch>,
	Chen-Yu Tsai <wens@...e.org>,
	Peter Griffin <peter.griffin@...aro.org>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] mmc: sunxi: Also set SDXC_LOW_POWER_ON

On 25 May 2015 at 09:02, Hans de Goede <hdegoede@...hat.com> 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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