linux-kernel - [PATCH] mmc: sdhci_am654: Add workaround for card detect debounce timer

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Message-ID: <20200729234130.25056-1-faiz_abbas@ti.com>
Date:   Thu, 30 Jul 2020 05:11:30 +0530
From:   Faiz Abbas <faiz_abbas@...com>
To:     <linux-kernel@...r.kernel.org>, <linux-mmc@...r.kernel.org>
CC:     <ulf.hansson@...aro.org>, <adrian.hunter@...el.com>,
        <faiz_abbas@...com>
Subject: [PATCH] mmc: sdhci_am654: Add workaround for card detect debounce timer

There is a one time delay because of a card detect debounce timer in the
controller IP. This timer runs as soon as power is applied to the module
regardless of whether a card is present or not and any writes to
SDHCI_POWER_ON will return 0 before it expires. This timeout has been
measured to be about 1 second in am654x and j721e.

Write-and-read-back in a loop on SDHCI_POWER_ON for a maximum of
1.5 seconds to make sure that the controller actually powers on.

Signed-off-by: Faiz Abbas <faiz_abbas@...com>
---
 drivers/mmc/host/sdhci_am654.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/drivers/mmc/host/sdhci_am654.c b/drivers/mmc/host/sdhci_am654.c
index 1718b9e8af63..55cff9de2f3e 100644
--- a/drivers/mmc/host/sdhci_am654.c
+++ b/drivers/mmc/host/sdhci_am654.c
@@ -272,6 +272,7 @@ static void sdhci_j721e_4bit_set_clock(struct sdhci_host *host,
 	sdhci_set_clock(host, clock);
 }
 
+#define MAX_POWER_ON_TIMEOUT	1500 /* ms */
 static void sdhci_am654_write_b(struct sdhci_host *host, u8 val, int reg)
 {
 	unsigned char timing = host->mmc->ios.timing;
@@ -291,6 +292,26 @@ static void sdhci_am654_write_b(struct sdhci_host *host, u8 val, int reg)
 	}
 
 	writeb(val, host->ioaddr + reg);
+	if (reg == SDHCI_POWER_CONTROL && (val & SDHCI_POWER_ON)) {
+		/*
+		 * Power on will not happen until the card detect debounce
+		 * timer expires. Wait at least 1.5 seconds for the power on
+		 * bit to be set
+		 */
+		ktime_t timeout = ktime_add_ms(ktime_get(),
+					       MAX_POWER_ON_TIMEOUT);
+		do {
+			if (ktime_compare(ktime_get(), timeout) > 0) {
+				dev_warn(mmc_dev(host->mmc),
+					 "Power on failed\n");
+
+				return;
+			}
+
+			writeb(val, host->ioaddr + reg);
+			usleep_range(1000, 10000);
+		} while (!(readb(host->ioaddr + reg) & SDHCI_POWER_ON));
+	}
 }
 
 static int sdhci_am654_execute_tuning(struct mmc_host *mmc, u32 opcode)
-- 
2.17.1