[PATCH 1/3] mmc: fix mmc mode selection for HS-DDR and higher

On Thu, Jun 2, 2016 at 2:58 AM, Bjorn Andersson
[off-list ref] wrote:

On Sun, May 29, 2016 at 12:04 AM, Chen-Yu Tsai [off-list ref] wrote:

quoted

When IS_ERR_VALUE was removed from the mmc core code, it was replaced
with a simple not-zero check. This does not work, as the value checked
is the return value for mmc_select_bus_width, which returns the set
bit width on success. This made eMMC modes higher than HS-DDR unusable.

Fix this by checking for a positive return value instead.

mmc_select_bus_width() can return 0 on "success" as well and the
previous check was !IS_ERR_VALUE(err), which coverts that. So I
believe these checks should be for err >= 0 rather than just > 0.

From the comments above the function:

"Zero is returned instead of error value if the wide width is not supported."

The documents I found, which were more vendor datasheets, only list
bit widths 4 and 8 for high speed SDR/DDR and HS200.

Not sure what the MMC spec actually says though, as I do not have
it.

Regards
ChenYu

Either way this fixes the boot failures seen on my Qualcomm based
boards with v4.7-rc1.

Regards,
Bjorn