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

Jaehoon Chung jh80.chung at samsung.com
Tue Sep 15 19:30:26 PDT 2015


On 09/16/2015 07:09 AM, Heiko Stübner wrote:
> 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 at chromium.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.

> 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?

Best Regards,
Jaehoon Chung

> Heiko

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