mmc: sdhci-of-at91: fix CALCR register being rewritten

When enabling calibration at reset, the CALCR register was completely
rewritten. This may cause certain bits being deleted unintentedly.
Fix by issuing a read-modify-write operation.

Fixes: 727d836a ("mmc: sdhci-of-at91: add DT property to enable calibration on full reset")
Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Link: https://lore.kernel.org/r/20200527105659.142560-1-eugen.hristev@microchip.com
Cc: stable@vger.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/sdhci-of-at91.c

@@ -121,9 +121,12 @@ static void sdhci_at91_reset(struct sdhci_host *host, u8 mask)
 	    || mmc_gpio_get_cd(host->mmc) >= 0)
 		sdhci_at91_set_force_card_detect(host);
 
-	if (priv->cal_always_on && (mask & SDHCI_RESET_ALL))
-		sdhci_writel(host, SDMMC_CALCR_ALWYSON | SDMMC_CALCR_EN,
+	if (priv->cal_always_on && (mask & SDHCI_RESET_ALL)) {
+		u32 calcr = sdhci_readl(host, SDMMC_CALCR);
+
+		sdhci_writel(host, calcr | SDMMC_CALCR_ALWYSON | SDMMC_CALCR_EN,
 			     SDMMC_CALCR);
+	}
 }
 
 static const struct sdhci_ops sdhci_at91_sama5d2_ops = {