From 8ccf96729972504acf4ca0e1868278ba549e0f5a Mon Sep 17 00:00:00 2001
From: Phil Elwell <phil@raspberrypi.org>
Date: Fri, 29 Sep 2017 10:32:19 +0100
Subject: [PATCH] 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>
---
 Documentation/devicetree/bindings/serial/pl011.yaml | 6 ++++++
 drivers/tty/serial/amba-pl011.c                     | 5 +++++
 2 files changed, 11 insertions(+)

--- a/Documentation/devicetree/bindings/serial/pl011.yaml
+++ b/Documentation/devicetree/bindings/serial/pl011.yaml
@@ -98,6 +98,12 @@ properties:
     $ref: /schemas/types.yaml#/definitions/uint32
     default: 3000
 
+  cts-event-workaround:
+    description:
+      Enables the (otherwise vendor-specific) workaround for the
+      CTS-induced TX lockup.
+    type: boolean
+
 required:
   - compatible
   - reg
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -2696,6 +2696,11 @@ static int pl011_probe(struct amba_devic
 	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);
