[Xen-devel] [PATCH v3 24/25] xen/vpl011: buffer out chars when the backend is xen

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

To avoid mixing the output of different domains on the console, buffer
the output chars and print line by line. Unless the domain has input
from the serial, in which case we want to print char by char for a
smooth user experience.

The size of SBSA_UART_OUT_BUF_SIZE is arbitrary. 90 should be large
enough to accommodate the length of most lines of output (typically they
are limited to 80 characters on Unix systems), plus one extra char for
the string terminator.

Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
---
 xen/arch/arm/vpl011.c        | 21 ++++++++++++++++++---
 xen/include/asm-arm/vpl011.h |  3 +++
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/xen/arch/arm/vpl011.c b/xen/arch/arm/vpl011.c
index f206c61..8137371 100644
--- a/xen/arch/arm/vpl011.c
+++ b/xen/arch/arm/vpl011.c
@@ -28,6 +28,7 @@
 #include <xen/lib.h>
 #include <xen/mm.h>
 #include <xen/sched.h>
+#include <xen/console.h>
 #include <public/domctl.h>
 #include <public/io/console.h>
 #include <asm/pl011-uart.h>
@@ -85,12 +86,26 @@ static void vpl011_write_data_xen(struct domain *d, uint8_t 
data)
 {
     unsigned long flags;
     struct vpl011 *vpl011 = &d->arch.vpl011;
+    struct vpl011_xen_backend *intf = vpl011->xen;
+    struct domain *input = console_input_domain();
 
     VPL011_LOCK(d, flags);
 
-    printk("%c", data);
-    if (data == '\n')
-        printk("DOM%u: ", d->domain_id);
+    intf->out[intf->out_prod++] = data;
+    if ( d == input && intf->out_prod == 1 )
+    {
+        printk("%c", data);
+        if ( data == '\n' )
+            printk("DOM%u: ", d->domain_id);
+        intf->out_prod = 0;
+    } else if ( d == input ||
+                intf->out_prod == SBSA_UART_OUT_BUF_SIZE - 1 ||
+                data == '\n' )
+    {
+        intf->out[intf->out_prod++] = '\0';
+        printk("DOM%u: %s", d->domain_id, intf->out);
+        intf->out_prod = 0;
+    }
 
     vpl011->uartris |= TXI;
     vpl011->uartfr &= ~TXFE;
diff --git a/xen/include/asm-arm/vpl011.h b/xen/include/asm-arm/vpl011.h
index c9918c1..30487e8 100644
--- a/xen/include/asm-arm/vpl011.h
+++ b/xen/include/asm-arm/vpl011.h
@@ -30,9 +30,12 @@
 #define VPL011_UNLOCK(d,flags) spin_unlock_irqrestore(&(d)->arch.vpl011.lock, 
flags)
 
 #define SBSA_UART_FIFO_SIZE 32
+#define SBSA_UART_OUT_BUF_SIZE 91
 struct vpl011_xen_backend {
     char in[SBSA_UART_FIFO_SIZE];
+    char out[SBSA_UART_OUT_BUF_SIZE];
     XENCONS_RING_IDX in_cons, in_prod;
+    XENCONS_RING_IDX out_prod;
 };
 
 struct vpl011 {
-- 
1.9.1


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