[U-Boot] [PATCH 1/2] arm: socfpga: mmc: Enable calibration for drvsel and smpsel

[Jaehoon Chung]

Hi,

On 09/04/2015 07:41 PM, Pavel Machek wrote:
> Hi!
> 
>>>>>>> How is this SMPLSEL and DRVSEL implemented on Exynos ?
>>>>>
>>>>> Exynos is using CLKSEL register in dw-mmc controller.
>>>>> It's exynos specific register in dwmmc controller. It's also
>>>>> represented 45 degree increment. SELCK_DRV is bit[18:16] or more.
>>>>> SELCLK_SAMPLE is bit[2:0] or more. There are other bits relevant to
>>>>> tuning clock. '_more_' means that it can be changed bandwidth.
>>>>>
>>>>> Anyway, I think there is no right method about finding the best smplclk
>>>>> and drvsel. If this is generic method, i will pick this. But i don't
>>>>> think so, and there is no benefit for exynos.
>>>>>
>>>>> smplclk and drvsel value need to process the tuning sequence.
>>>>> There is no tuning case at bootloader, since it's not implemented about
>>>>> HS200 or upper mode.
>>>>>
>>>>> Clksel an drvsel value are passed by device tree.
>>>>
>>>> In that case, maybe SoCFPGA should also pick those values from DT ? It
>>>> would keep the code simple and in case there is a problematic board, it
>>>> could use u-boot application to perform the tuning.
>>>
>>> I prefer not to do that as it narrows the supported use case for the
>>> driver.
>>
>> How so? It keeps the driver code clean and this code you're adding seems
>> like a special-purpose stuff which needs to be done once for particular
>> board, no ?
> 
> Well... stuff that can be automatically detected is not supposed to be
> in the device tree.
> 
> clksel and drvsel can be calibrated, so I see some arguments why we
> should calibrate them, and not hardcode them in the device tree.

My opinions are 

1. This code is not generic dwmmc code. So i don't want to locate into dwmmc core.
If need to apply, i agree that it applies this in socfpga-dw_mmc.c.

2. In exynos, value of devcie-tree is the tested value.
After has tested with every values, it defined the best value into device-tree.
(Working fine with values.)
At every time, it doesn't need to detect the best value with same SoC.
(Especially, at bootloader)

3. In my experiment, there should be side-effect during finding best sample/drv value.

4. If HS200 or upper mode is supported at bootloader, it needs the tuning sequence.
Then it needs to find the best sampl/drv values. but it doesn't support HS200 or other at bootloader.

5. Affect at booting time??


Best Regards,
Jaehoon Chung

> 									Pavel
>