serial: 8250_dw: Add optional reset control support

The Allwinner A31 and A23 SoCs have a reset controller
maintaining the UART in reset by default.

This patch adds optional reset support to the driver.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 10 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt b/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt
index 095ac7172ffe..7f76214f728a 100644
--- a/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt
+++ b/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt
@@ -15,6 +15,7 @@ The supplying peripheral clock can also be handled, needing a second property
         Required elements: "baudclk", "apb_pclk"
 
 Optional properties:
+- resets : phandle to the parent reset controller.
 - reg-shift : quantity to shift the register offsets by.  If this property is
   not present then the register offsets are not shifted.
 - reg-io-width : the size (in bytes) of the IO accesses that should be
diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index affdcb192aed..501db2f58fd2 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -26,6 +26,7 @@
 #include <linux/slab.h>
 #include <linux/acpi.h>
 #include <linux/clk.h>
+#include <linux/reset.h>
 #include <linux/pm_runtime.h>
 
 #include <asm/byteorder.h>
@@ -60,6 +61,7 @@ struct dw8250_data {
         int                     line;
         struct clk              *clk;
         struct clk              *pclk;
+        struct reset_control    *rst;
         struct uart_8250_dma    dma;
 };
 
@@ -383,6 +385,10 @@ static int dw8250_probe(struct platform_device *pdev)
                 }
         }
 
+        data->rst = devm_reset_control_get_optional(&pdev->dev, NULL);
+        if (!IS_ERR(data->rst))
+                reset_control_deassert(data->rst);
+
         data->dma.rx_chan_id = -1;
         data->dma.tx_chan_id = -1;
         data->dma.rx_param = data;
@@ -426,6 +432,9 @@ static int dw8250_remove(struct platform_device *pdev)
 
         serial8250_unregister_port(data->line);
 
+        if (!IS_ERR(data->rst))
+                reset_control_assert(data->rst);
+
         if (!IS_ERR(data->pclk))
                 clk_disable_unprepare(data->pclk);