linux-kernel - [PATCH 3.16 297/370] mmc: core: fix multi-bit bus width without high-speed mode

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Message-ID: <lsq.1489146383.257710347@decadent.org.uk>
Date:   Fri, 10 Mar 2017 11:46:23 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Anssi Hannula" <anssi.hannula@...wise.fi>,
        "Ulf Hansson" <ulf.hansson@...aro.org>
Subject: [PATCH 3.16 297/370] mmc: core: fix multi-bit bus width without
 high-speed mode

3.16.42-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Anssi Hannula <anssi.hannula@...wise.fi>

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@...wise.fi>
Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 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
@@ -1391,10 +1391,10 @@ static int mmc_init_card(struct mmc_host
 		err = mmc_select_hs400(card);
 		if (err)
 			goto err;
-	} 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 err;