mmc: sdhci-esdhc-imx: allow 1.8V modes without 100/200MHz pinctrl states

commit 92748beac07c471d995fbec642b63572dc01b3dc upstream.

If pinctrl nodes for 100/200MHz are missing, the controller should
not select any mode which need signal frequencies 100MHz or higher.
To prevent such speed modes the driver currently uses the quirk flag
SDHCI_QUIRK2_NO_1_8_V. This works nicely for SD cards since 1.8V
signaling is required for all faster modes and slower modes use 3.3V
signaling only.

However, there are eMMC modes which use 1.8V signaling and run below
100MHz, e.g. DDR52 at 1.8V. With using SDHCI_QUIRK2_NO_1_8_V this
mode is prevented. When using a fixed 1.8V regulator as vqmmc-supply
the stack has no valid mode to use. In this tenuous situation the
kernel continuously prints voltage switching errors:
  mmc1: Switching to 3.3V signalling voltage failed

Avoid using SDHCI_QUIRK2_NO_1_8_V and prevent faster modes by
altering the SDHCI capability register. With that the stack is able
to select 1.8V modes even if no faster pinctrl states are available:
  # cat /sys/kernel/debug/mmc1/ios
  ...
  timing spec:    8 (mmc DDR52)
  signal voltage: 1 (1.80 V)
  ...

Link: http://lkml.kernel.org/r/20180628081331.13051-1-stefan@agner.ch
Signed-off-by: Stefan Agner <stefan@agner.ch>
Fixes: ad93220de7da ("mmc: sdhci-esdhc-imx: change pinctrl state according
to uhs mode")
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
[bwh: Backported to 3.16:
 - There is no SDHCI_SUPPORT_HS400 flag to clear
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

1 files changed, 9 insertions, 9 deletions

diff --git a/drivers/mmc/host/sdhci-esdhc-imx.c b/drivers/mmc/host/sdhci-esdhc-imx.c
index ccec0e32590f..8f9012130a3a 100644
--- a/drivers/mmc/host/sdhci-esdhc-imx.c
+++ b/drivers/mmc/host/sdhci-esdhc-imx.c
@@ -261,6 +261,15 @@ static u32 esdhc_readl_le(struct sdhci_host *host, int reg)
 				val = SDHCI_SUPPORT_DDR50 | SDHCI_SUPPORT_SDR104
 					| SDHCI_SUPPORT_SDR50
 					| SDHCI_USE_SDR50_TUNING;
+
+			/*
+			 * Do not advertise faster UHS modes if there are no
+			 * pinctrl states for 100MHz/200MHz.
+			 */
+			if (IS_ERR_OR_NULL(imx_data->pins_100mhz) ||
+			    IS_ERR_OR_NULL(imx_data->pins_200mhz))
+				val &= ~(SDHCI_SUPPORT_SDR50 | SDHCI_SUPPORT_DDR50
+					 | SDHCI_SUPPORT_SDR104);
 		}
 	}
 
@@ -1108,15 +1117,6 @@ static int sdhci_esdhc_imx_probe(struct platform_device *pdev)
 						ESDHC_PINCTRL_STATE_100MHZ);
 		imx_data->pins_200mhz = pinctrl_lookup_state(imx_data->pinctrl,
 						ESDHC_PINCTRL_STATE_200MHZ);
-		if (IS_ERR(imx_data->pins_100mhz) ||
-				IS_ERR(imx_data->pins_200mhz)) {
-			dev_warn(mmc_dev(host->mmc),
-				"could not get ultra high speed state, work on normal mode\n");
-			/* fall back to not support uhs by specify no 1.8v quirk */
-			host->quirks2 |= SDHCI_QUIRK2_NO_1_8_V;
-		}
-	} else {
-		host->quirks2 |= SDHCI_QUIRK2_NO_1_8_V;
 	}
 
 	err = sdhci_add_host(host);