xen/arm: initialize vpl011 flag register

The tx/rx fifo flags were not set when the vpl011 is initialized. This
is a problem for certain guests that are operating in polled mode, as a
guest will generally check the rx fifo empty flag to determine if there
is data before doing a read. The result is a continuous spam of the
message "vpl011: Unexpected IN ring buffer empty" before the first valid
character is received. This initializes the flag status register to the
default specified in the PL011 technical reference manual.

Signed-off-by: Jeff Kubascik <jeff.kubascik@dornerworks.com>
Acked-by: Julien Grall <julien@xen.org>

diff --git a/xen/arch/arm/vpl011.c b/xen/arch/arm/vpl011.c
index 7bc5eeb207b67c142297d1d75915c53a1366615d..895f436cc49e22ce0d3625f06d57fe28657edb61 100644 (file)
--- a/xen/arch/arm/vpl011.c
+++ b/xen/arch/arm/vpl011.c
@@ -668,6 +668,8 @@ int domain_vpl011_init(struct domain *d, struct vpl011_init_info *info)
         goto out2;
     }
 
+    vpl011->uartfr = TXFE | RXFE;
+
     spin_lock_init(&vpl011->lock);
 
     register_mmio_handler(d, &vpl011_mmio_handler,