[RFC][PATCH] Fix for Intel Baytrail-T errata regarding the non-functioning mmc_pwr pin

[Jon Pry <jonpry@gmail.com>]

This bug effects Asus T100 as well as other Baytrail-T devices. 
Erratum in question can be found at 
http://www.intel.com/content/dam/www/public/us/en/documents/specification-updates/atom-Z36xxx-Z37xxx-spec-update.pdf

Signed-off-by: Jon Pry <jonpry <at> gmail.com>
---
diff --git a/drivers/mmc/host/sdhci-acpi.c b/drivers/mmc/host/sdhci-acpi.c
index ebb3f39..ebed2a0 100644
--- a/drivers/mmc/host/sdhci-acpi.c
+++ b/drivers/mmc/host/sdhci-acpi.c
@@ -123,7 +123,7 @@ static const struct sdhci_acpi_slot sdhci_acpi_slot_int_emmc = {
 
 static const struct sdhci_acpi_slot sdhci_acpi_slot_int_sdio = {
 	.quirks  = SDHCI_QUIRK_BROKEN_CARD_DETECTION,
-	.quirks2 = SDHCI_QUIRK2_HOST_OFF_CARD_ON,
+	.quirks2 = SDHCI_QUIRK2_HOST_OFF_CARD_ON | SDHCI_QUIRK2_BROKEN_POWER_ENABLE,
 	.caps    = MMC_CAP_NONREMOVABLE | MMC_CAP_POWER_OFF_CARD,
 	.flags   = SDHCI_ACPI_RUNTIME_PM,
 	.pm_caps = MMC_PM_KEEP_POWER,
diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index 9a79fc4..5a0e928 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -22,6 +22,7 @@
 #include <linux/scatterlist.h>
 #include <linux/regulator/consumer.h>
 #include <linux/pm_runtime.h>
+#include <linux/gpio.h>
 
 #include <linux/leds.h>
 
@@ -1261,6 +1262,10 @@ static inline void sdhci_update_clock(struct sdhci_host *host)
 	sdhci_set_clock(host, clock);
 }
 
+static inline void sdhci_set_power_quirk(unsigned short power) {
+	gpio_set_value(SDHCI_POWER_QUIRK_GPIO, power);
+}
+
 static int sdhci_set_power(struct sdhci_host *host, unsigned short power)
 {
 	u8 pwr = 0;
@@ -1292,6 +1297,9 @@ static int sdhci_set_power(struct sdhci_host *host, unsigned short power)
 		sdhci_writeb(host, 0, SDHCI_POWER_CONTROL);
 		if (host->quirks2 & SDHCI_QUIRK2_CARD_ON_NEEDS_BUS_ON)
 			sdhci_runtime_pm_bus_off(host);
+		/* The intel Bay Trail SoCs need to assert a GPIO as a work around */
+		if (host->quirks2 & SDHCI_QUIRK2_BROKEN_POWER_ENABLE)
+			sdhci_set_power_quirk(0);
 		return 0;
 	}
 
@@ -1311,8 +1319,14 @@ static int sdhci_set_power(struct sdhci_host *host, unsigned short power)
 
 	pwr |= SDHCI_POWER_ON;
 
+
 	sdhci_writeb(host, pwr, SDHCI_POWER_CONTROL);
 
+	/* The intel Bay Trail SoCs need to assert a GPIO as a work around */
+	if (host->quirks2 & SDHCI_QUIRK2_BROKEN_POWER_ENABLE)
+		sdhci_set_power_quirk(1);
+
+
 	if (host->quirks2 & SDHCI_QUIRK2_CARD_ON_NEEDS_BUS_ON)
 		sdhci_runtime_pm_bus_on(host);
 
@@ -2820,6 +2841,18 @@ int sdhci_add_host(struct sdhci_host *host)
 		host->flags &= ~SDHCI_USE_SDMA;
 	}
 
+    if ((host->quirks2 & SDHCI_QUIRK2_BROKEN_POWER_ENABLE)) {
+        printk("Using GPIO for power enable as it is marked broken\n");
+        if (gpio_request(SDHCI_POWER_QUIRK_GPIO, "SDIO_PWR_EN") < 0) {
+            printk("Unable to request GPIO. SDIO may be broken.");
+			host->quirks2 = host->quirks2 & ~SDHCI_QUIRK2_BROKEN_POWER_ENABLE;
+        }
+        else if (gpio_direction_output(SDHCI_POWER_QUIRK_GPIO, 0) < 0) {
+            printk("Unable to set GPIO direction. SDIO may be broken.");
+			host->quirks2 = host->quirks2 & ~SDHCI_QUIRK2_BROKEN_POWER_ENABLE;
+        }
+    }
+
 	if ((host->version >= SDHCI_SPEC_200) &&
 		(caps[0] & SDHCI_CAN_DO_ADMA2))
 		host->flags |= SDHCI_USE_ADMA;
@@ -3325,6 +3358,10 @@ void sdhci_remove_host(struct sdhci_host *host, int dead)
 	tasklet_kill(&host->card_tasklet);
 	tasklet_kill(&host->finish_tasklet);
 
+    if (host->quirks2 & SDHCI_QUIRK2_BROKEN_POWER_ENABLE) {
+        gpio_free(SDHCI_POWER_QUIRK_GPIO);
+    }
+
 	if (host->vmmc) {
 		regulator_disable(host->vmmc);
 		regulator_put(host->vmmc);
diff --git a/drivers/mmc/host/sdhci.h b/drivers/mmc/host/sdhci.h
index 0a3ed01..027fcd1 100644
--- a/drivers/mmc/host/sdhci.h
+++ b/drivers/mmc/host/sdhci.h
@@ -84,11 +84,12 @@
 #define   SDHCI_CTRL_ADMA64	0x18
 #define   SDHCI_CTRL_8BITBUS	0x20
 
 #define SDHCI_POWER_CONTROL	0x29
 #define  SDHCI_POWER_ON		0x01
 #define  SDHCI_POWER_180	0x0A
 #define  SDHCI_POWER_300	0x0C
 #define  SDHCI_POWER_330	0x0E
+#define SDHCI_POWER_QUIRK_GPIO 195 /*GPIO offset 41 of SCORE device is SD3_PWR_EN*/
 
 #define SDHCI_BLOCK_GAP_CONTROL	0x2A
 
diff --git a/include/linux/mmc/sdhci.h b/include/linux/mmc/sdhci.h
index 7be12b8..92cec16 100644
--- a/include/linux/mmc/sdhci.h
+++ b/include/linux/mmc/sdhci.h
@@ -102,6 +102,9 @@ struct sdhci_host {
 #define SDHCI_QUIRK2_BROKEN_HS200			(1<<6)
 /* Controller does not support DDR50 */
 #define SDHCI_QUIRK2_BROKEN_DDR50			(1<<7)
+/* Controller cannot initialize power (must use GPIO instead) */
+#define SDHCI_QUIRK2_BROKEN_POWER_ENABLE		(1<<8)
+
 
 	int irq;		/* Device IRQ */
 	void __iomem *ioaddr;	/* Mapped address */