[PATCH] mmc: dw_mmc: fix card read threshold for PIO mode

[Shawn Guo]

Hi Alim,

On Sat, Nov 22, 2014 at 06:56:46PM +0530, Alim Akhtar wrote:
> Hi Shawn,
> 
> On Sat, Nov 22, 2014 at 5:01 AM, Shawn Guo <shawn.guo at linaro.org> wrote:
> > Seungwon, Jaehoon,
> >
> > On Fri, Nov 21, 2014 at 02:39:10PM +0800, Shawn Guo wrote:
> >> Commit f1d2736c8156 ("mmc: dw_mmc: control card read threshold")
> >> introduces a regression for use case where PIO mode is used, i.e.
> >> CONFIG_MMC_DW_IDMAC is not disabled.  It stops kernel from booting
> >
> > s/not disabled/disabled
> >
> >> like below.
> >
> > For understanding the problem better, can you guys please to test the
> > dw_mmc driver on Samsung platforms with CONFIG_MMC_DW_IDMAC disabled.
> > I'm wondering this is a problem specific to my platform or a common one.
> >
> I tested PIO mode on exynos5800-peach-pi board with Ulf's -next
> branch, and it works fine.
> To confirm PIO mode works, I ran iozone and it gave  low performance
> number (as expected) then IDMA mode.

Thanks a lot for testing and confirming that it works on exynos.

> 
> One thing to note, is your controller version is 210a, so not sure if
> something more in missing from driver.

Unfortunately, I do not have the reference manual for the hardware I'm
running so far.  But from the kernel log, the controller version is
210a.  What do you mean by "something more in missing from driver"?
The driver has any limitation for any particular controller versions?

One thing I need to check with hardware vendor is whether register
CDTHRCTL is available on my dwmmc controller.  From my testing, even
reading this register every time dw_mci_submit_data() is called causes
problem for me.

> Also from log its looks like you card clock is 26Mhz, did you tried
> running at 52Mhz?

I did not.  But it's unlikely the problem of clock frequency from what
I've seen.

Shawn