[PATCH 4.4 15/15] mmc: core: fix multi-bit bus width without high-speed mode

From: Greg Kroah-Hartman
Date: Tue Feb 21 2017 - 08:12:57 EST

4.4-stable review patch. If anyone has any objections, please let me know.


From: Anssi Hannula <anssi.hannula@xxxxxxxxxx>

commit 3d4ef329757cfd5e0b23cce97cdeca7e2df89c99 upstream.

Commit 577fb13199b1 ("mmc: rework selection of bus speed mode")
refactored bus width selection code to mmc_select_bus_width().

However, it also altered the behavior to not call the selection code in
non-high-speed modes anymore.

This causes 1-bit mode to always be used when the high-speed mode is not
enabled, even though 4-bit and 8-bit bus are valid bus widths in the
backwards-compatibility (legacy) mode as well (see e.g. 5.3.2 Bus Speed
Modes in JEDEC 84-B50). This results in a significant regression in
transfer speeds.

Fix the code to allow 4-bit and 8-bit widths even without high-speed
mode, as before.

Tested with a Zynq-7000 PicoZed 7020 board.

Fixes: 577fb13199b1 ("mmc: rework selection of bus speed mode")
Signed-off-by: Anssi Hannula <anssi.hannula@xxxxxxxxxx>
Signed-off-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
[anssi.hannula@xxxxxxxxxx: backported for the different err variable
check on v4.4 and tested]
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

Here is a trivial backport as the upstream commit did not apply cleanly
to 4.4-stable.

drivers/mmc/core/mmc.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -1581,10 +1581,10 @@ static int mmc_init_card(struct mmc_host
err = mmc_select_hs400(card);
if (err)
goto free_card;
- } else if (mmc_card_hs(card)) {
+ } else {
/* Select the desired bus width optionally */
err = mmc_select_bus_width(card);
- if (!IS_ERR_VALUE(err)) {
+ if (!IS_ERR_VALUE(err) && mmc_card_hs(card)) {
err = mmc_select_hs_ddr(card);
if (err)
goto free_card;