ACPI / LPSS: not using UART RTS override with Auto Flow Control

Adding a check for UART Auto Flow Control feature and only
enabling the RTS override when it's not supported. RTS
override is not needed when Auto Flow Control is used and
they shouldn't be used together.
Signed-off-by: NHeikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/acpi_lpss.c

@@ -83,18 +83,26 @@ struct lpss_private_data {
 	u32 prv_reg_ctx[LPSS_PRV_REG_COUNT];
 };
 
+/* UART Component Parameter Register */
+#define LPSS_UART_CPR			0xF4
+#define LPSS_UART_CPR_AFCE		BIT(4)
+
 static void lpss_uart_setup(struct lpss_private_data *pdata)
 {
 	unsigned int offset;
-	u32 reg;
+	u32 val;
 
 	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);
+	val = readl(pdata->mmio_base + offset);
+	writel(val | LPSS_TX_INT_MASK, pdata->mmio_base + offset);
+
+	val = readl(pdata->mmio_base + LPSS_UART_CPR);
+	if (!(val & LPSS_UART_CPR_AFCE)) {
+		offset = pdata->dev_desc->prv_offset + LPSS_GENERAL;
+		val = readl(pdata->mmio_base + offset);
+		val |= LPSS_GENERAL_UART_RTS_OVRD;
+		writel(val, pdata->mmio_base + offset);
+	}
 }
 
 static void byt_i2c_setup(struct lpss_private_data *pdata)