linux-kernel - Re: [patch 7/8] SDHCI: Add change

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Message-ID: <20081221150741.74e0b558@mjolnir.drzeus.cx>
Date:	Sun, 21 Dec 2008 15:07:41 +0100
From:	Pierre Ossman <drzeus@...eus.cx>
To:	Ben Dooks <ben-linux@...ff.org>
Cc:	sdhci-devel@...t.drzeus.cx, linux-kernel@...r.kernel.org,
	Ben Dooks <ben-linux@...ff.org>
Subject: Re: [patch 7/8] SDHCI: Add change_clock callback for glue drivers

On Tue, 02 Dec 2008 15:40:25 +0000
Ben Dooks <ben-linux@...ff.org> wrote:

> Add a change_clock callback to allow drivers to update
> device specific clock selections and control registers
> when there is a change in clock.
> 
> Move the main part of sdhci_set_clock() to a new routine
> which can be called by the glue drivers to do the sdhci
> standard clock management.
> 
> Update the sdhci-s3c driver to use this to select the
> appropriate clock source when clocks change.
> 
> Signed-off-by: Ben Dooks <ben-linux@...ff.org>
> 

I'm still waiting for a proper description of things here.

Looking at the code, it looks like you have multiple clock sources and
selecting the best one dynamically. That's probably a nice feature, but
it should be possible to solve whilst still keeping calls going only
from sdhci to sdhci-s3c.

E.g. we could add a caps field (to keep quirks just for bugs) which
states "has multiple clock sources". Before the core changes the clock,
it calls ops->select_clock(target_hz), which changes clock source and
returns the new base frequency.

Rgds
-- 
     -- Pierre Ossman

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