ACPI / LPSS: fix UART Auto Flow Control

There is an additional bit in the GENERAL register on newer
silicon that needs to be set or UART's RTS pin fails to
reflect the flow control settings in the Modem Control
Register.

This will fix an issue where the RTS pin of the UART stays
always at 1.8V, regardless of the register settings.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/acpi_lpss.c

@@ -30,6 +30,7 @@ ACPI_MODULE_NAME("acpi_lpss");
 /* Offsets relative to LPSS_PRIVATE_OFFSET */
 #define LPSS_GENERAL			0x08
 #define LPSS_GENERAL_LTR_MODE_SW	BIT(2)
+#define LPSS_GENERAL_UART_RTS_OVRD	BIT(3)
 #define LPSS_SW_LTR			0x10
 #define LPSS_AUTO_LTR			0x14
 #define LPSS_TX_INT			0x20
@@ -68,11 +69,16 @@ struct lpss_private_data {
 
 static void lpss_uart_setup(struct lpss_private_data *pdata)
 {
-	unsigned int tx_int_offset = pdata->dev_desc->prv_offset + LPSS_TX_INT;
+	unsigned int offset;
 	u32 reg;
 
-	reg = readl(pdata->mmio_base + tx_int_offset);
-	writel(reg | LPSS_TX_INT_MASK, pdata->mmio_base + tx_int_offset);
+	offset = pdata->dev_desc->prv_offset + LPSS_TX_INT;
+	reg = readl(pdata->mmio_base + offset);
+	writel(reg | LPSS_TX_INT_MASK, pdata->mmio_base + offset);
+
+	offset = pdata->dev_desc->prv_offset + LPSS_GENERAL;
+	reg = readl(pdata->mmio_base + offset);
+	writel(reg | LPSS_GENERAL_UART_RTS_OVRD, pdata->mmio_base + offset);
 }
 
 static struct lpss_device_desc lpt_dev_desc = {