linux-kernel - [RFC PATCH V3 13/21] mmc: sdhci: UHS-II support, skip signal_voltage

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Date:   Fri, 10 Jul 2020 19:11:04 +0800
From:   Ben Chuang <benchuanggli@...il.com>
To:     adrian.hunter@...el.com, ulf.hansson@...aro.org
Cc:     linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        ben.chuang@...esyslogic.com.tw, takahiro.akashi@...aro.org,
        greg.tu@...esyslogic.com.tw, Ben Chuang <benchuanggli@...il.com>
Subject: [RFC PATCH V3 13/21] mmc: sdhci: UHS-II support, skip signal_voltage_switch()

From: AKASHI Takahiro <takahiro.akashi@...aro.org>

sdhci_start_signal_voltage_switch() should be called only in UHS-I mode,
and not for UHS-II mode.

Signed-off-by: Ben Chuang <ben.chuang@...esyslogic.com.tw>
Signed-off-by: AKASHI Takahiro <takahiro.akashi@...aro.org>
---
 drivers/mmc/host/sdhci.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index 5511649946b9..7f2537648a08 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -2623,8 +2623,13 @@ int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
 	/*
 	 * Signal Voltage Switching is only applicable for Host Controllers
 	 * v3.00 and above.
+	 * But for UHS2, the signal voltage is supplied by vdd2 which is
+	 * already 1.8v so no voltage switch required.
 	 */
-	if (host->version < SDHCI_SPEC_300)
+	if (host->version < SDHCI_SPEC_300 ||
+	    (IS_ENABLED(CONFIG_MMC_SDHCI_UHS2) &&
+	     host->version >= SDHCI_SPEC_400 &&
+	     host->mmc->flags & MMC_UHS2_SUPPORT))
 		return 0;
 
 	ctrl = sdhci_readw(host, SDHCI_HOST_CONTROL2);
-- 
2.27.0