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

[Chin Liang See <clsee@altera.com>]

Hi,

On Mon, 2015-09-07 at 03:33 +0000, Jaehoon Chung wrote:
> 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.
> 

Yup, let move that to socfpga-dw_mmc.c as majority believe that is
correct way to move forward. I shall send in v3 which integrate Pavel's
comment in v2

> 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.
> 

Yah, normally it will not need that.
As we are catering for various customer board design, this calibration
will help even they routed the SDMMC slot few inches away.

> 5. Affect at booting time??

We measured this before and it took around ~5.2ms for worst case.

Thanks
Chin Liang

> 
> 
> Best Regards,
> Jaehoon Chung
> 
> > 									Pavel
> > 
>