linux-kernel - RE: [RFC] sdhci: use ios->clock to know when sdhci is idle

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Date:	Thu, 30 Dec 2010 18:37:39 +0800
From:	"Gao, Yunpeng" <yunpeng.gao@...el.com>
To:	Linus Walleij <linus.ml.walleij@...il.com>
CC:	Pierre Tardy <tardyp@...il.com>,
	"Yuan, Hang" <hang.yuan@...el.com>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Chris Ball <cjb@...top.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Cox <alan@...ux.intel.com>, Takashi Iwai <tiwai@...e.de>,
	Maxim Levitsky <maximlevitsky@...il.com>,
	Ohad Ben-Cohen <ohad@...ery.com>
Subject: RE: [RFC] sdhci: use ios->clock to know when sdhci is idle

>> So, why we have to move to the 'aggressive clock gating framework'?
>
>The aggressive clock gating makes more sense since the different
>drivers will know better how to handle the gating. ios with f=0 can
>be interpreted differently. Else every driver has to register
>runtime PM hooks for this, which is less elegant.

Thanks for the response. I just curious that is this the only reason to change the framework? To my understanding, seems it's not a very strong reason :-)

Take the example of sd/mmc card -
by using the aggressive clock gating framework, it means the host controller will gate (clock gating or power gating) itself if not receiving requests for 8 clocks even if the request queue of mmc block driver is not empty at that time. So the host controller has to be gated / ungated repeatedly until the current request queue of mmc block driver becomes empty. I don't think this is elegant since most of the gating / ungating operations are not necessary.

Instead, if we do it in the mmc block driver by just call the pm_runtime_put() once the current request queue is empty and call pm_runtime_get() once any new request comes, then the host controller can be gated/ungated appropriately.

Thanks.

Regards,
Yunpeng
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