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

[Chin Liang See]

Hi,

On Thu, 2015-09-03 at 11:37 +0200, marex at denx.de wrote:
> On Thursday, September 03, 2015 at 07:30:08 AM, Jaehoon Chung wrote:
> > Hi,
> 
> Hi,
> 
> > On 09/03/2015 09:27 AM, Chin Liang See wrote:
> > > On Wed, 2015-09-02 at 12:32 +0200, marex at denx.de wrote:
> > [snip]
> 
> thanks
> 
> > >>>>> Would want to hear more from Jaehoon as Exynos and SOCFPGA are the
> > >>>>> one setting up these values.
> > >>>> 
> > >>>> Since this approach is not based on dwmmc TRM, it's based on SOCFPGA
> > >>>> SoC, i think that it doesn't need to include into dwmmc core.
> > >>>> If need to located into dwmmc core, this code needs to modify more.
> > >>>> 
> > >>>> As drvsel and clksmpl are used at Exynos and SoCFPGA, it's not core
> > >>>> feature. Other SoC can't be used them. we don't know.
> > >>> 
> > >>> Plus the way that this function is implemented, it is very specific to
> > >>> SoCFGA, as the tables and rows are representing 45 degree increments
> > >>> for the drvsel and smplsel value. Other platforms can have either more
> > >>> or less granularity in the drvsel and smplsel values.
> > >> 
> > >> 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.

Thanks
Chin Liang

> 
> Best regards,
> Marek Vasut