amba_pl011: Add cts-event-workaround DT property

The BCM2835 PL011 implementation seems to have a bug that can lead to a
transmission lockup if CTS changes frequently. A workaround was added to
the driver with a vendor-specific flag to enable it, but this flag is
currently not set for ARM implementations.

Add a "cts-event-workaround" property to Pi DTBs and use the presence
of that property to force the flag to be enabled in the driver.

See: https://github.com/raspberrypi/linux/issues/1280

Signed-off-by: Phil Elwell <phil@raspberrypi.org>

diff --git a/Documentation/devicetree/bindings/serial/pl011.yaml b/Documentation/devicetree/bindings/serial/pl011.yaml
index 5ea00f8..8df2883 100644 (file)
--- a/Documentation/devicetree/bindings/serial/pl011.yaml
+++ b/Documentation/devicetree/bindings/serial/pl011.yaml
@@ -91,6 +91,12 @@ properties:
       3000ms.
     default: 3000
 
+  cts-event-workaround:
+    description:
+      Enables the (otherwise vendor-specific) workaround for the
+      CTS-induced TX lockup.
+    type: boolean
+
 required:
   - compatible
   - reg

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index a8193f6..2304975 100644 (file)
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -2824,6 +2824,11 @@ static int pl011_probe(struct amba_device *dev, const struct amba_id *id)
        if (IS_ERR(uap->clk))
                return PTR_ERR(uap->clk);
 
+       if (of_property_read_bool(dev->dev.of_node, "cts-event-workaround")) {
+           vendor->cts_event_workaround = true;
+           dev_info(&dev->dev, "cts_event_workaround enabled\n");
+       }
+
        uap->reg_offset = vendor->reg_offset;
        uap->vendor = vendor;
        uap->fifosize = vendor->get_fifosize(dev);