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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Jisheng Zhang <Jisheng.Zhang@synaptics.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Ulf Hansson <ulf.hansson@linaro.org>
Subject: [PATCH 5.4 198/214] mmc: sdhci: Use Auto CMD Auto Select only when v4_mode is true
Date:   Tue,  3 Nov 2020 21:37:26 +0100
Message-Id: <20201103203309.204457298@linuxfoundation.org>
In-Reply-To: <20201103203249.448706377@linuxfoundation.org>
References: <20201103203249.448706377@linuxfoundation.org>
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From: Jisheng Zhang <Jisheng.Zhang@synaptics.com>

commit b3e1ea16fb39fb6e1a1cf1dbdd6738531de3dc7d upstream.

sdhci-of-dwcmshc meets an eMMC read performance regression with below
command after commit 427b6514d095 ("mmc: sdhci: Add Auto CMD Auto
Select support"):

dd if=/dev/mmcblk0 of=/dev/null bs=8192 count=100000

Before the commit, the above command gives 120MB/s
After the commit, the above command gives 51.3 MB/s

So it looks like sdhci-of-dwcmshc expects Version 4 Mode for Auto
CMD Auto Select. Fix the performance degradation by ensuring v4_mode
is true to use Auto CMD Auto Select.

Fixes: 427b6514d095 ("mmc: sdhci: Add Auto CMD Auto Select support")
Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20201015174115.4cf2c19a@xhacker.debian
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/mmc/host/sdhci.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -1162,9 +1162,11 @@ static inline void sdhci_auto_cmd_select
 	/*
 	 * In case of Version 4.10 or later, use of 'Auto CMD Auto
 	 * Select' is recommended rather than use of 'Auto CMD12
-	 * Enable' or 'Auto CMD23 Enable'.
+	 * Enable' or 'Auto CMD23 Enable'. We require Version 4 Mode
+	 * here because some controllers (e.g sdhci-of-dwmshc) expect it.
 	 */
-	if (host->version >= SDHCI_SPEC_410 && (use_cmd12 || use_cmd23)) {
+	if (host->version >= SDHCI_SPEC_410 && host->v4_mode &&
+	    (use_cmd12 || use_cmd23)) {
 		*mode |= SDHCI_TRNS_AUTO_SEL;
 
 		ctrl2 = sdhci_readw(host, SDHCI_HOST_CONTROL2);