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

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Message-ID: <5566CC0C.1050103@redhat.com>
Date:	Thu, 28 May 2015 10:04:28 +0200
From:	Hans de Goede <hdegoede@...hat.com>
To:	Ulf Hansson <ulf.hansson@...aro.org>
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

Hi,

On 28-05-15 10:02, Ulf Hansson wrote:
> 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!?

Removing it now sounds like a good plan to me, we would still need
to look into maybe enabling SDXC_LOW_POWER_ON on sunxi in some cases
to save power, but that is an orthogonal problem.

Regards,

Hans
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