Julien Grall
2013-May-23 14:50 UTC
[PATCH] xen/arm: avoid lost characters with early_printk
Introduce the function early_flush to wait until the UART has finished to
transfer the character.
When early printk is enabled, it''s possible to loose the last
characters if:
- the UART is initialized by the UART driver
- Xen hang
This is result to a truncated message. To be sure that the message is fully
transfered by early_printk, add a call to early_flush. This will avoid lost
characters.
Signed-off-by: Julien Grall <julien.grall@linaro.org>
---
xen/arch/arm/arm32/debug.S | 7 +++++++
xen/arch/arm/arm64/debug.S | 7 +++++++
xen/arch/arm/early_printk.c | 7 +++++++
3 files changed, 21 insertions(+)
diff --git a/xen/arch/arm/arm32/debug.S b/xen/arch/arm/arm32/debug.S
index 1bfbfc1..92f5724 100644
--- a/xen/arch/arm/arm32/debug.S
+++ b/xen/arch/arm/arm32/debug.S
@@ -32,6 +32,13 @@ early_putch:
early_uart_transmit r1, r0
mov pc, lr
+.globl early_flush
+/* Flush the UART - this function is called by C */
+early_flush:
+ ldr r1, =FIXMAP_ADDR(FIXMAP_CONSOLE) /* r1 := VA UART base address
*/
+ early_uart_ready r1, r2
+ mov pc, lr
+
/*
* Local variables:
* mode: ASM
diff --git a/xen/arch/arm/arm64/debug.S b/xen/arch/arm/arm64/debug.S
index 38b7c74..c7b5e6c 100644
--- a/xen/arch/arm/arm64/debug.S
+++ b/xen/arch/arm/arm64/debug.S
@@ -32,6 +32,13 @@ early_putch:
early_uart_transmit x15, w0
ret
+.globl early_flush
+/* Flush the UART - this function is called by C */
+early_flush:
+ ldr x15, =FIXMAP_ADDR(FIXMAP_CONSOLE) /* x15 := VA UART base address
*/
+ early_uart_ready x15, 1
+ ret
+
/*
* Local variables:
* mode: ASM
diff --git a/xen/arch/arm/early_printk.c b/xen/arch/arm/early_printk.c
index 5950323..ca151a5 100644
--- a/xen/arch/arm/early_printk.c
+++ b/xen/arch/arm/early_printk.c
@@ -16,6 +16,7 @@
#include <asm/early_printk.h>
void early_putch(char c);
+void early_flush(void);
/* Early printk buffer */
static char __initdata buf[512];
@@ -34,6 +35,12 @@ static void __init early_vprintk(const char *fmt, va_list
args)
{
vsnprintf(buf, sizeof(buf), fmt, args);
early_puts(buf);
+
+ /*
+ * Wait the UART has finished to transfer all characters before
+ * to continue. This will avoid lost characters if Xen abort.
+ */
+ early_flush();
}
void __init early_printk(const char *fmt, ...)
--
1.7.10.4
Ian Campbell
2013-May-30 09:00 UTC
Re: [PATCH] xen/arm: avoid lost characters with early_printk
On Thu, 2013-05-23 at 15:50 +0100, Julien Grall wrote:> Introduce the function early_flush to wait until the UART has finished to > transfer the character. > When early printk is enabled, it''s possible to loose the last characters if: > - the UART is initialized by the UART driver > - Xen hang > > This is result to a truncated message. To be sure that the message is fully > transfered by early_printk, add a call to early_flush. This will avoid lost > characters. > > Signed-off-by: Julien Grall <julien.grall@linaro.org>Acked + applied, thanks.