Hello,

I have a Dell Latitude E7450 with a O2 Micro, SD/MMC Card Reader
[1217:8520] card reader. When I insert my Sandisk ultra 64GB microSD
(with a SD card adapter) I get the following errors.

Dmesg output after I insert the SD card:

[  306.054203] sdhci: Timeout waiting for Buffer Read Ready interrupt
during tuning procedure, falling back to fixed sampling clock
[  306.055982] mmc0: tuning execution failed
[  306.055987] mmc0: error -5 whilst initialising SD card
[  306.466185] sdhci: Timeout waiting for Buffer Read Ready interrupt
during tuning procedure, falling back to fixed sampling clock
[  306.467964] mmc0: tuning execution failed
[  306.467970] mmc0: error -5 whilst initialising SD card
[  306.890205] sdhci: Timeout waiting for Buffer Read Ready interrupt
during tuning procedure, falling back to fixed sampling clock
[  306.891993] mmc0: tuning execution failed
[  306.892005] mmc0: error -5 whilst initialising SD card
[  307.330197] sdhci: Timeout waiting for Buffer Read Ready interrupt
during tuning procedure, falling back to fixed sampling clock
[  307.331980] mmc0: tuning execution failed
[  307.331990] mmc0: error -5 whilst initialising SD card

I used the latest mainline kernel available to me [1]
$ uname -a
Linux cosmo 4.4.0-040400rc4-generic #201512061930 SMP Mon Dec 7
00:32:31 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

It was working fine for kernel versions older than 4.1.8.

I did a bisection and here is the first bad commit

> e6c69099f63c84e1825c0f742a76ff4a8afeaa9b is the first bad commit
> commit e6c69099f63c84e1825c0f742a76ff4a8afeaa9b
> Author: Adam Lee <adam.lee@canonical.com>
> Date:   Mon Aug 3 14:33:28 2015 +0800
>
>     mmc: sdhci-pci: set the clear transfer mode register quirk for O2Micro
>
>     commit 143b648ddf1583905fa15d32be27a31442fc7933 upstream.
>
>     This patch fixes MMC not working issue on O2Micro/BayHub Host, which
>     requires transfer mode register to be cleared when sending no DMA
>     command.
>
>     Signed-off-by: Peter Guo <peter.guo@bayhubtech.com>
>     Signed-off-by: Adam Lee <adam.lee@canonical.com>
>     Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
>     Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

I originally logged this issue to the Ubuntu bug tracker[2], but it
appears to be an upstream issue and so I was instructed to report
here.
Please note that I use the latest Bios version for the model.

$ sudo dmidecode -s bios-version;sudo dmidecode -s bios-release-date
A08
10/28/2015

[1] http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.4-rc4-wily/
[2] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1523178

Thanks,
Alex