linux-kernel - Re: [linux-sunxi] [PATCH 3/3] mmc: sunxi: use controller automatic clock gating.

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Message-ID: <55CB3D92.6040403@redhat.com>
Date:	Wed, 12 Aug 2015 14:35:30 +0200
From:	Hans de Goede <hdegoede@...hat.com>
To:	hramrach@...il.com, linux-sunxi@...glegroups.com,
	Seungwon Jeon <tgih.jun@...sung.com>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	David Lanzendörfer <david.lanzendoerfer@....ch>,
	Chen-Yu Tsai <wens@...e.org>, Arnd Bergmann <arnd@...db.de>,
	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [linux-sunxi] [PATCH 3/3] mmc: sunxi: use controller automatic
 clock gating.

Hi,

On 12-08-15 14:23, Michal Suchanek wrote:
> When core does not set the MMC_QUIRK_BROKEN_CLK_GATING flag enable
> automatic hardware controlled clock gating on the mmc interface.
>
> Signed-off-by: Michal Suchanek <hramrach@...il.com>

In general this looks good, but I wonder how intensively this has
been tested ? Also given the long latencies when using manual
clock on/off support, have you done any testing to check what
sort of latencies this adds, e.g. Both with and without
the patch, dump all the filesystem caches:

echo 3 > /proc/sys/vm/drop_caches

And then do:

time cat /some/small/file/on/the/sdcard

Do this at least 3 time both with and without the patch, and see
if there are any noticable differences ?

Regards,

Hans



> ---
>   drivers/mmc/host/sunxi-mmc.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/mmc/host/sunxi-mmc.c b/drivers/mmc/host/sunxi-mmc.c
> index f808a02..443cab5 100644
> --- a/drivers/mmc/host/sunxi-mmc.c
> +++ b/drivers/mmc/host/sunxi-mmc.c
> @@ -601,8 +601,13 @@ static int sunxi_mmc_oclk_onoff(struct sunxi_mmc_host *host, u32 oclk_en)
>   	rval = mmc_readl(host, REG_CLKCR);
>   	rval &= ~(SDXC_CARD_CLOCK_ON | SDXC_LOW_POWER_ON);
>
> -	if (oclk_en)
> +	if (oclk_en) {
>   		rval |= SDXC_CARD_CLOCK_ON;
> +		if (!host->mmc->card ||
> +		     !(host->mmc->card->quirks & MMC_QUIRK_BROKEN_CLK_GATING))
> +
> +			rval |= SDXC_LOW_POWER_ON;
> +	}
>
>   	start = jiffies;
>   	end = start + msecs_to_jiffies(750);
>
--
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