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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,
        Eugen Hristev <eugen.hristev@microchip.com>,
        Karl Olsen <karl@micro-technic.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.15 481/779] mmc: sdhci-of-at91: fix set_uhs_signaling rewriting of MC1R
Date:   Mon, 15 Aug 2022 20:02:05 +0200
Message-Id: <20220815180357.816841310@linuxfoundation.org>
In-Reply-To: <20220815180337.130757997@linuxfoundation.org>
References: <20220815180337.130757997@linuxfoundation.org>
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From: Eugen Hristev <eugen.hristev@microchip.com>

[ Upstream commit 5987e6ded29d52e42fc7b06aa575c60a25eee38e ]

In set_uhs_signaling, the DDR bit is being set by fully writing the MC1R
register.
This can lead to accidental erase of certain bits in this register.
Avoid this by doing a read-modify-write operation.

Fixes: d0918764c17b ("mmc: sdhci-of-at91: fix MMC_DDR_52 timing selection")
Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Tested-by: Karl Olsen <karl@micro-technic.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20220630090926.15061-1-eugen.hristev@microchip.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/mmc/host/sdhci-of-at91.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/mmc/host/sdhci-of-at91.c b/drivers/mmc/host/sdhci-of-at91.c
index d1a1c548c515..0452c312b65e 100644
--- a/drivers/mmc/host/sdhci-of-at91.c
+++ b/drivers/mmc/host/sdhci-of-at91.c
@@ -100,8 +100,13 @@ static void sdhci_at91_set_clock(struct sdhci_host *host, unsigned int clock)
 static void sdhci_at91_set_uhs_signaling(struct sdhci_host *host,
 					 unsigned int timing)
 {
-	if (timing == MMC_TIMING_MMC_DDR52)
-		sdhci_writeb(host, SDMMC_MC1R_DDR, SDMMC_MC1R);
+	u8 mc1r;
+
+	if (timing == MMC_TIMING_MMC_DDR52) {
+		mc1r = sdhci_readb(host, SDMMC_MC1R);
+		mc1r |= SDMMC_MC1R_DDR;
+		sdhci_writeb(host, mc1r, SDMMC_MC1R);
+	}
 	sdhci_set_uhs_signaling(host, timing);
 }
 
-- 
2.35.1