[PATCH] mmc: sdhci: make sure SDHCI_CLOCK_CARD_EN bit sticks

[Jean-Francois Dagenais <jeff.dagenais@gmail.com>]

Regardless of the broken-cd quirk, when it silently doesn't stick,
no clock is applied to the bus lines, yet the code continues to
try to make CMDs and times out after 10 seconds for each. This
process can take up to a minute as mmc_rescan_try_freq tries the
different commands to discover the card.

Short of changing sdhci_enable_clk's signature chain in all
dependent drivers, at least provide a hint that this might be the
problem. This will save tons of time for system integrators.

Signed-off-by: Jean-Francois Dagenais <jeff.dagenais@gmail.com>
---
 drivers/mmc/host/sdhci.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index 63db84481dff..d1e8eac6b15f 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -1894,6 +1894,22 @@ void sdhci_enable_clk(struct sdhci_host *host, u16 clk)
 
 	clk |= SDHCI_CLOCK_CARD_EN;
 	sdhci_writew(host, clk, SDHCI_CLOCK_CONTROL);
+
+	wmb();
+
+	clk = sdhci_readw(host, SDHCI_CLOCK_CONTROL);
+	if (clk & SDHCI_CLOCK_CARD_EN)
+		return;
+
+	/* The controller will clear this bit if card absent condition is
+	 * detected. If card is indeed present, check platform configuration for
+	 * how CD is reported to the SDHCI host controller. There may be an
+	 * "assume present" mechanism in the platform registers, or your pin mux
+	 * may be incorrect.
+	 */
+	pr_err("%s: SDHCI_CLOCK_CARD_EN bit did not stick. Card absent?\n",
+		mmc_hostname(host->mmc));
+	sdhci_dumpregs(host);
 }
 EXPORT_SYMBOL_GPL(sdhci_enable_clk);
 
-- 
2.25.0