amba_pl011: Add cts-event-workaround DT property

Phil Elwell · popcornmix · commit 39ec3b8d17c6 · 2021-01-27T19:12:48.000Z
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: raspberrypi/linux#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
@@ -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
diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
@@ -2686,6 +2686,11 @@ 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);
