[PATCH] mmc: core: improve fallback in mmc_select_timing()

From: Heiner Kallweit <hkallweit1@gmail.com>
To: Ulf Hansson <ulf.hansson@linaro.org>
Cc: "linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>
Subject: [PATCH] mmc: core: improve fallback in mmc_select_timing()
Date: Fri, 18 Feb 2022 08:00:45 +0100	[thread overview]
Message-ID: <fae9ee4b-6b93-95ac-abf3-f97c62e07b9d@gmail.com> (raw)

I have a system (cheap Amlogic S905W based TV box) where the eMMC chip
refuses to switch to HS200 timing. That's not nice, but my bigger
problem is that the system then falls back to the very slow default
mode, even though DDR52 is supported and works well.

Therefore, if setting a mode fails with EBADMSG (switch error), try the
next (in descending performance order) mode instead of immediately
falling back to the slowest mode.

With the patch it looks like this on my system:

mmc1: mmc_select_hs200 failed, error -74
mmc1: new DDR MMC card at address 0001
mmcblk1: mmc1:0001 DG4008 7.28 GiB

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
---
 drivers/mmc/core/mmc.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index bbbbcaf70..c0272192d 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -1523,11 +1523,23 @@ static int mmc_select_timing(struct mmc_card *card)
 	if (!mmc_can_ext_csd(card))
 		goto bus_speed;
 
-	if (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS400ES)
+	if (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS400ES) {
 		err = mmc_select_hs400es(card);
-	else if (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS200)
+		if (!err)
+			goto bus_speed;
+		if (err != -EBADMSG)
+			return err;
+	}
+
+	if (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS200) {
 		err = mmc_select_hs200(card);
-	else if (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS)
+		if (!err)
+			goto bus_speed;
+		if (err != -EBADMSG)
+			return err;
+	}
+
+	if (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS)
 		err = mmc_select_hs(card);
 
 	if (err && err != -EBADMSG)
-- 
2.35.1

