+static int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
+ struct mmc_ios *ios)
+{
+ struct sdhci_host *host;
+ u8 pwr;
+ u16 clk, ctrl;
+ u32 present_state;
+
+ host = mmc_priv(mmc);
+
+ /*
+ * Signal Voltage Switching is only applicable for Host Controllers
+ * v3.00 and above.
+ */
+ if (host->version < SDHCI_SPEC_300)
+ return 0;
+
+ /*
+ * We first check whether the request is to set signalling voltage
+ * to 3.3V. If so, we change the voltage to 3.3V and return quickly.
+ */
+ ctrl = sdhci_readw(host, SDHCI_HOST_CONTROL2);
+ if (ios->signal_voltage == MMC_SIGNAL_VOLTAGE_330) {
+ /* Set 1.8V Signal Enable in the Host Control2 register to 0 */
+ ctrl &= ~SDHCI_CTRL_VDD_180;
+ sdhci_writew(host, ctrl, SDHCI_HOST_CONTROL2);
+
+ /* Wait for 5ms */
+ usleep_range(5000, 5500);
+
+ /* 3.3V regulator output should be stable within 5 ms */
+ ctrl = sdhci_readw(host, SDHCI_HOST_CONTROL2);
+ if (!(ctrl & SDHCI_CTRL_VDD_180))
+ return 0;
+ else {
+ printk(KERN_INFO DRIVER_NAME ": Switching to 3.3V "
+ "signalling voltage failed\n");
+ return -EIO;
+ }
+ } else if (!(ctrl & SDHCI_CTRL_VDD_180) &&
+ (ios->signal_voltage == MMC_SIGNAL_VOLTAGE_180)) {
+ /* Stop SDCLK */
+ clk = sdhci_readw(host, SDHCI_CLOCK_CONTROL);
+ clk &= ~SDHCI_CLOCK_CARD_EN;
+ sdhci_writew(host, clk, SDHCI_CLOCK_CONTROL);
+
+ /* Check whether DAT[3:0] is 0000 */
+ present_state = sdhci_readl(host, SDHCI_PRESENT_STATE);
+ if (!((present_state & SDHCI_DATA_LVL_MASK) >>
+ SDHCI_DATA_LVL_SHIFT)) {
+ /*
+ * Enable 1.8V Signal Enable in the Host Control2
+ * register
+ */
+ ctrl |= SDHCI_CTRL_VDD_180;
+ sdhci_writew(host, ctrl, SDHCI_HOST_CONTROL2);
+
+ /* Wait for 5ms */
+ usleep_range(5000, 5500);
+
+ ctrl = sdhci_readw(host, SDHCI_HOST_CONTROL2);
+ if (ctrl & SDHCI_CTRL_VDD_180) {
+ /* Provide SDCLK again and wait for 1ms*/
+ clk = sdhci_readw(host, SDHCI_CLOCK_CONTROL);
+ clk |= SDHCI_CLOCK_CARD_EN;
+ sdhci_writew(host, clk, SDHCI_CLOCK_CONTROL);
+ usleep_range(1000, 1500);
+
+ /*
+ * If DAT[3:0] level is 1111b, then the card
+ * was successfully switched to 1.8V signaling.
+ */
+ present_state = sdhci_readl(host,
+ SDHCI_PRESENT_STATE);
+ if ((present_state & SDHCI_DATA_LVL_MASK) ==
+ SDHCI_DATA_LVL_MASK)
+ return 0;
+ }
+ }
+
+ /*
+ * If we are here, that means the switch to 1.8V signaling
+ * failed. We power cycle the card, and retry initialization
+ * sequence by setting S18R to 0.
+ */
+ pwr = sdhci_readb(host, SDHCI_POWER_CONTROL);
+ pwr &= ~SDHCI_POWER_ON;
+ sdhci_writeb(host, pwr, SDHCI_POWER_CONTROL);
+
+ /* Wait for 1ms as per the spec */
+ usleep_range(1000, 1500);
+ pwr |= SDHCI_POWER_ON;
+ sdhci_writeb(host, pwr, SDHCI_POWER_CONTROL);
+
+ printk(KERN_INFO DRIVER_NAME ": Switching to 1.8V signalling "
+ "voltage failed, retrying with S18R set to 0\n");
+ return -EAGAIN;
+ } else
+ /* No signal voltage switch required */
+ return 0;
+}
+