linux-kernel - Re: [PATCH 6/8] mmc: dw_mmc: Generic MMC tuning with the clock phase framework

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Date:	Wed, 16 Sep 2015 00:09 +0200
From:	Heiko Stübner <heiko@...ech.de>
To:	Jaehoon Chung <jh80.chung@...sung.com>
Cc:	ulf.hansson@...aro.org, mturquette@...libre.com,
	sboyd@...eaurora.org, linux-mmc@...r.kernel.org,
	linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Alexandru M Stan <amstan@...omium.org>,
	CPGS <cpgs@...sung.com>
Subject: Re: [PATCH 6/8] mmc: dw_mmc: Generic MMC tuning with the clock phase framework

Hi,

Am Dienstag, 15. September 2015, 17:25:38 schrieb Jaehoon Chung:
> On 09/01/2015 03:24 AM, Heiko Stuebner wrote:
> > From: Alexandru M Stan <amstan@...omium.org>
> > 
> > This algorithm will try 1 degree increments, since there's no way to tell
> > what resolution the underlying phase code uses. As an added bonus, doing
> > many tunings yields better results since some tests are run more than once
> > (ex: if the underlying driver uses 45 degree increments, the tuning code
> > will try the same angle more than once).
> > 
> > It will then construct a list of good phase ranges (even ranges that cross
> > 360/0), will pick the biggest range then it will set the sample_clk to the
> > middle of that range.
> > 
> > We do not touch ciu_drive (and by extension define default-drive-phase).
> > Drive phase is mostly used to define minimum hold times, while one could
> > write some code to determine what phase meets the minimum hold time (ex 10
> > degrees) this will not work with the current clock phase framework (which
> > floors angles, so we'll get 0 deg, and there's no way to know what
> > resolution the floors happen at). We assume that the default drive angles
> > set by the hardware are good enough.
> > 
> > If a device has device specific code (like exynos) then that will still
> > take precedence, otherwise this new code will execute. If the device wants
> > to tune, but has no sample_clk defined we'll return EIO with an error
> > message.
> 
> Which point is "_generic_"? I don't find the code that control the register
> relevant to CLK_DRV/SMPL PHASE. It seems that posted the similar patches at
> u-boot mailing list..

The "generic" part is that it uses the clk phase API for dw_mmc 
implementations where the clkgen controlling interface is outside the dw_mmc 
IP itself. So it's open for other implementations as well.

But if you are more comfortable with it, I can also move it into the dw_mmc-
rockchip variant for the time being, until another user comes along.


Heiko

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