[xen stable-4.13] xen/arm: initialize vpl011 flag register

[patchbot@xxxxxxx]

commit c0dad816c6de702ddbe87908a9e5ab12f83c397f
Author:     Jeff Kubascik <jeff.kubascik@xxxxxxxxxxxxxxx>
AuthorDate: Mon Nov 25 15:58:00 2019 -0500
Commit:     Stefano Stabellini <sstabellini@xxxxxxxxxx>
CommitDate: Fri Apr 10 09:29:25 2020 -0700

    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@xxxxxxxxxxxxxxx>
    Acked-by: Julien Grall <julien@xxxxxxx>
    (cherry picked from commit b4637ed6cd5375f04ac51d6b900a9ccad6c6c03a)
---
 xen/arch/arm/vpl011.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/xen/arch/arm/vpl011.c b/xen/arch/arm/vpl011.c
index 7bc5eeb207..895f436cc4 100644
--- 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,
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.13