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

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Message-ID: <2272810.k4vHSW5D0y@diego>
Date:	Wed, 16 Sep 2015 16:52:26 +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 Mittwoch, 16. September 2015, 11:30:26 schrieb Jaehoon Chung:
> On 09/16/2015 07:09 AM, Heiko Stübner wrote:
> > 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.
> 
> Designware IP also has the CLK phase register(UHS_REG_EXT register)...
> if this code is related with it, it should be located into dw-mmc.c.

UHS_REG_EXT is acutally "reserved" on both the rk3288 as well as the rk3368. 
rk3036/rk3128 (Cortex-A7) provide a bit description, but the tuning 
documentation still uses the controls located in the clock controller.

So I guess UHS_REG_EXT is the real "generic" solution.

> > 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.
> I think more better that this code is located into dw_mmc-rockchip. how
> about?

As described above, moving that to the rockchip part sounds sensible. And I 
guess we can think more about it, once a second user appears.


Heiko
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