linux-kernel - Re: [PATCH 2/3] mmc: dw_mmc: simplify the SDMMC_CLKEN_LOW

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Date:	Mon, 17 Aug 2015 16:55:46 +0200
From:	Michal Suchanek <hramrach@...il.com>
To:	Alim Akhtar <alim.akhtar@...il.com>
Cc:	Jaehoon Chung <jh80.chung@...sung.com>,
	linux-sunxi <linux-sunxi@...glegroups.com>,
	Seungwon Jeon <tgih.jun@...sung.com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	David Lanzendörfer <david.lanzendoerfer@....ch>,
	Hans de Goede <hdegoede@...hat.com>,
	Chen-Yu Tsai <wens@...e.org>, Arnd Bergmann <arnd@...db.de>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/3] mmc: dw_mmc: simplify the SDMMC_CLKEN_LOW_PWR logic

 Hello,

On 17 August 2015 at 16:42, Alim Akhtar <alim.akhtar@...il.com> wrote:
> HI
>
> On Mon, Aug 17, 2015 at 4:56 PM, Jaehoon Chung <jh80.chung@...sung.com> wrote:
>> On 08/17/2015 02:52 PM, Michal Suchanek wrote:
>>> Hello,
>>>
>>> On 17 August 2015 at 03:55, Jaehoon Chung <jh80.chung@...sung.com> wrote:
>>>> Hi, Michal.
>>>>
>>>> On 08/12/2015 09:23 PM, Michal Suchanek wrote:
>>>>> The driver has open-coded test for SDIO cards. Use the mmc core provided
>>>>> MMC_QUIRK_BROKEN_CLK_GATING flag instead.
>>>>
>>>> Did you use the clock-gating for SDIO cards?
>>>> Doesn't MMC_CAP_SDIO_IRQ bit set? Which case is broken?
>>>> Could you explain to me more?
>>>
>>> The core flag for disabling power saving is MMC_QUIRK_BROKEN_CLK_GATING.
>>
>> I understood your intention. And i read the comment into mmc/core/quirks.c
>> I will test SDIO card with this patch. Thanks.
>>
> When you test, please check if SDIO IRQ still works, we need to put
> dw_mmc in low_power mode otherwise SDIO IRQ will be not be generated
> by dw_mmc host controller.
>

As far as I understand the logic which is removed in this patch and
the core logic which replaces it is the same -  low power by means of
clock gating is *not* enabled for SDIO cards in either case.

The original code also checks for SDIO IRQ and disables clock gating
regardless of card type which is probably redundant. If not it should
be fixed in mmc core.

My recent kernel builds which I run on a system with mwifiex card
probably include this patch.

Thanks

Michal
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