mmc: core: Fixup signal voltage switch

When switching SD and SDIO cards from 3.3V to 1.8V signal levels, the
clock should be gated for 5 ms during the step. After enabling the
clock, the host should wait for at least 1 ms before checking for
failure. Failure by the card to switch is indicated by dat[0:3] being
pulled low. The host should check for this condition and power-cycle
the card if failure is indicated.

Add a retry mechanism for the SDIO case.

If the voltage switch fails repeatedly, give up and continue the
initialization using the original voltage.

This patch places a couple of requirements on the host driver:

 1) mmc_set_ios with ios.clock = 0 must gate the clock
 2) mmc_power_off must actually cut the power to the card
 3) The card_busy host_ops member must be implemented

if these requirements are not fulfilled, the 1.8V signal voltage switch
will still be attempted but may not be successful.

Signed-off-by: Johan Rudholm <johan.rudholm@stericsson.com>
Signed-off-by: Kevin Liu <kliu5@marvell.com>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Wei WANG <wei_wang@realsil.com.cn>
Signed-off-by: Chris Ball <cjb@laptop.org>

1 files changed, 73 insertions, 10 deletions

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index bb794c784597..e41badbf9b50 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -1340,6 +1340,7 @@ int mmc_set_signal_voltage(struct mmc_host *host, int signal_voltage)
 {
 	struct mmc_command cmd = {0};
 	int err = 0;
+	u32 clock;
 
 	BUG_ON(!host);
 
@@ -1347,20 +1348,82 @@ int mmc_set_signal_voltage(struct mmc_host *host, int signal_voltage)
 	 * Send CMD11 only if the request is to switch the card to
 	 * 1.8V signalling.
 	 */
-	if (signal_voltage != MMC_SIGNAL_VOLTAGE_330) {
-		cmd.opcode = SD_SWITCH_VOLTAGE;
-		cmd.arg = 0;
-		cmd.flags = MMC_RSP_R1 | MMC_CMD_AC;
+	if (signal_voltage == MMC_SIGNAL_VOLTAGE_330)
+		return __mmc_set_signal_voltage(host, signal_voltage);
 
-		err = mmc_wait_for_cmd(host, &cmd, 0);
-		if (err)
-			return err;
+	/*
+	 * If we cannot switch voltages, return failure so the caller
+	 * can continue without UHS mode
+	 */
+	if (!host->ops->start_signal_voltage_switch)
+		return -EPERM;
+	if (!host->ops->card_busy)
+		pr_warning("%s: cannot verify signal voltage switch\n",
+				mmc_hostname(host));
+
+	cmd.opcode = SD_SWITCH_VOLTAGE;
+	cmd.arg = 0;
+	cmd.flags = MMC_RSP_R1 | MMC_CMD_AC;
+
+	err = mmc_wait_for_cmd(host, &cmd, 0);
+	if (err)
+		return err;
 
-		if (!mmc_host_is_spi(host) && (cmd.resp[0] & R1_ERROR))
-			return -EIO;
+	if (!mmc_host_is_spi(host) && (cmd.resp[0] & R1_ERROR))
+		return -EIO;
+
+	mmc_host_clk_hold(host);
+	/*
+	 * The card should drive cmd and dat[0:3] low immediately
+	 * after the response of cmd11, but wait 1 ms to be sure
+	 */
+	mmc_delay(1);
+	if (host->ops->card_busy && !host->ops->card_busy(host)) {
+		err = -EAGAIN;
+		goto power_cycle;
 	}
+	/*
+	 * During a signal voltage level switch, the clock must be gated
+	 * for 5 ms according to the SD spec
+	 */
+	clock = host->ios.clock;
+	host->ios.clock = 0;
+	mmc_set_ios(host);
 
-	return __mmc_set_signal_voltage(host, signal_voltage);
+	if (__mmc_set_signal_voltage(host, signal_voltage)) {
+		/*
+		 * Voltages may not have been switched, but we've already
+		 * sent CMD11, so a power cycle is required anyway
+		 */
+		err = -EAGAIN;
+		goto power_cycle;
+	}
+
+	/* Keep clock gated for at least 5 ms */
+	mmc_delay(5);
+	host->ios.clock = clock;
+	mmc_set_ios(host);
+
+	/* Wait for at least 1 ms according to spec */
+	mmc_delay(1);
+
+	/*
+	 * Failure to switch is indicated by the card holding
+	 * dat[0:3] low
+	 */
+	if (host->ops->card_busy && host->ops->card_busy(host))
+		err = -EAGAIN;
+
+power_cycle:
+	if (err) {
+		pr_debug("%s: Signal voltage switch failed, "
+			"power cycling card\n", mmc_hostname(host));
+		mmc_power_cycle(host);
+	}
+
+	mmc_host_clk_release(host);
+
+	return err;
 }
 
 /*