Patch "mmc: core: fix multi-bit bus width without high-speed mode" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

mmc: core: fix multi-bit bus width without high-speed mode

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mmc-core-fix-multi-bit-bus-width-without-high-speed-mode.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Anssi Hannula <[email protected]>
Date: Mon, 13 Feb 2017 13:46:41 +0200
Subject: mmc: core: fix multi-bit bus width without high-speed mode

From: Anssi Hannula <[email protected]>

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.

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

@@ -1690,10 +1690,10 @@ 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 (err > 0) {
+		if (err > 0 && mmc_card_hs(card)) {
 			err = mmc_select_hs_ddr(card);
 			if (err)
 				goto free_card;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/mmc-core-fix-multi-bit-bus-width-without-high-speed-mode.patch