linux-kernel - [PATCH] mmc: core: Improve fallback to speed modes if eMMC HS200 fails

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Date:   Thu,  3 Mar 2022 17:45:22 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     linux-mmc@...r.kernel.org, Ulf Hansson <ulf.hansson@...aro.org>,
        Heiner Kallweit <hkallweit1@...il.com>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Yann Gautier <yann.gautier@...s.st.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] mmc: core: Improve fallback to speed modes if eMMC HS200 fails

In the error path of mmc_select_hs200() we are trying our best to restore
the card/host into a valid state. This makes sense, especially if we
encounter a simple switch error (-EBADMSG). However, rather than then
continue with using the legacy speed mode, let's try the other better speed
modes first. Additionally, let's update the card->mmc_avail_type to avoid
us from trying a broken HS200 mode again.

In an Amlogic S905W based TV box where the switch to HS200 mode fails for
the eMMC, this allows us to use the eMMC in DDR mode in favor of the legacy
mode, which greatly improves the performance.

Suggested-by: Heiner Kallweit <hkallweit1@...il.com>
Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
---
 drivers/mmc/core/mmc.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index 141f851c9f58..6e7db45cb8e0 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -1518,13 +1518,23 @@ 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)
+		goto out;
+	}
+
+	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 == -EBADMSG)
+			card->mmc_avail_type &= ~EXT_CSD_CARD_TYPE_HS200;
+		else
+			goto out;
+	}
+
+	if (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS)
 		err = mmc_select_hs(card);
 
+out:
 	if (err && err != -EBADMSG)
 		return err;
 
-- 
2.25.1