linux-kernel - [PATCH 3/3] mmc: sdhci-esdhc-imx: prevent stack from using higher speed modes

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Date:   Thu, 28 Jun 2018 10:13:31 +0200
From:   Stefan Agner <stefan@...er.ch>
To:     adrian.hunter@...el.com, ulf.hansson@...aro.org
Cc:     fabio.estevam@....com, haibo.chen@....com, aisheng.dong@....com,
        michael@...rulasolutions.com, rmk+kernel@...linux.org.uk,
        linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Stefan Agner <stefan@...er.ch>
Subject: [PATCH 3/3] mmc: sdhci-esdhc-imx: prevent stack from using higher speed modes

If pinctrl configurations for higher speed modes are missing, the
stack currently uses the no 1.8V quirk. This comes close to what
we need but not exactly: E.g. if a eMMC chip uses 1.8V signaling
(by specifying a 1.8V only vqmmc-supply) while not providing any
100MHz/200MHz pinctrl configurations then the SDHCI_QUIRK2_NO_1_8_V
leads the stack to print signaling voltage switch failed errors
continuously:
  mmc1: Switching to 3.3V signalling voltage failed

Presumably because the stack tries to use 3.3V signaling:

  # cat /sys/kernel/debug/mmc1/ios
  ...
  timing spec:    8 (mmc DDR52)
  signal voltage: 0 (3.30 V)
  ...

With using SDHCI_QUIRK2_NO_UHS_HS200_HS400 we prevent the stack
from choosing any modes require speeds higher than 52MHz while
still allowing to select modes using 1.8V at lower speeds (e.g.
DDR52):

  # cat /sys/kernel/debug/mmc1/ios
  ...
  timing spec:    8 (mmc DDR52)
  signal voltage: 1 (1.80 V)
  ...

Signed-off-by: Stefan Agner <stefan@...er.ch>
---
 drivers/mmc/host/sdhci-esdhc-imx.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/mmc/host/sdhci-esdhc-imx.c b/drivers/mmc/host/sdhci-esdhc-imx.c
index 20a420b765b3..4a1c33018072 100644
--- a/drivers/mmc/host/sdhci-esdhc-imx.c
+++ b/drivers/mmc/host/sdhci-esdhc-imx.c
@@ -1165,10 +1165,10 @@ sdhci_esdhc_imx_probe_dt(struct platform_device *pdev,
 			 * fall back to not supporting uhs by specifying no
 			 * 1.8v quirk
 			 */
-			host->quirks2 |= SDHCI_QUIRK2_NO_1_8_V;
+			host->quirks2 |= SDHCI_QUIRK2_NO_UHS_HS200_HS400;
 		}
 	} else {
-		host->quirks2 |= SDHCI_QUIRK2_NO_1_8_V;
+		host->quirks2 |= SDHCI_QUIRK2_NO_UHS_HS200_HS400;
 	}

 	/* call to generic mmc_of_parse to support additional capabilities */
-- 
2.18.0