[xen master] xen/arm: vpl011: Do not try to handle TX FIFO status when backend in Xen

[patchbot@xxxxxxx]

commit 1213ebfb9f35920b3e0f5dff71bb917f5fb4be5f
Author:     Michal Orzel <michal.orzel@xxxxxxx>
AuthorDate: Wed Apr 5 13:17:50 2023 +0200
Commit:     Stefano Stabellini <stefano.stabellini@xxxxxxx>
CommitDate: Mon Apr 17 13:01:34 2023 -0700

    xen/arm: vpl011: Do not try to handle TX FIFO status when backend in Xen
    
    >From vpl011_rx_char_xen(), we call vpl011_data_avail() that handles both
    RX and TX state. Because we are passing 0 as out_fifo_level and
    SBSA_UART_FIFO_SIZE as out_size, we end up calling a function
    vpl011_update_tx_fifo_status() which performs TXI bit handling
    depending on the FIFO trigger level. This does not make sense when backend
    is in Xen, as we maintain a single TX state where data can always be
    written and as such there is no TX FIFO handling. Furthermore, this
    function assumes that the backend is in domain by making use of struct
    xencons_interface unconditionally. Fix it by calling this function only
    when backend is in domain. Also add an assert for sanity.
    
    Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
    Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
    Tested-by: Henry Wang <Henry.Wang@xxxxxxx>
---
 xen/arch/arm/vpl011.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/vpl011.c b/xen/arch/arm/vpl011.c
index ff06deeb64..7856b4b5f5 100644
--- a/xen/arch/arm/vpl011.c
+++ b/xen/arch/arm/vpl011.c
@@ -261,6 +261,9 @@ static void vpl011_update_tx_fifo_status(struct vpl011 
*vpl011,
     struct xencons_interface *intf = vpl011->backend.dom.ring_buf;
     unsigned int fifo_threshold = sizeof(intf->out) - SBSA_UART_FIFO_LEVEL;
 
+    /* No TX FIFO handling when backend is in Xen */
+    ASSERT(vpl011->backend_in_domain);
+
     BUILD_BUG_ON(sizeof(intf->out) < SBSA_UART_FIFO_SIZE);
 
     /*
@@ -547,7 +550,13 @@ static void vpl011_data_avail(struct domain *d,
          */
         vpl011->uartfr &= ~BUSY;
 
-        vpl011_update_tx_fifo_status(vpl011, out_fifo_level);
+        /*
+         * When backend is in Xen, we are always ready for new data to be
+         * written (i.e. no TX FIFO handling), therefore we do not want
+         * to change the TX FIFO status in such case.
+         */
+        if ( vpl011->backend_in_domain )
+            vpl011_update_tx_fifo_status(vpl011, out_fifo_level);
     }
 
     vpl011_update_interrupt_status(d);
--
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