[PATCH 06/18] Blackfin Serial Driver: explain why we cannot cpu_relax() in early serial code

Bryan Wu
2009-03-06T06:42:41Z

From: Mike Frysinger <vapier.adi@gmail.com>

Signed-off-by: Mike Frysinger <vapier.adi@gmail.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
---
drivers/serial/bfin_5xx.c | 4 ++++
1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/drivers/serial/bfin_5xx.c b/drivers/serial/bfin_5xx.c
index 5a163f6..de8709d 100644
--- a/drivers/serial/bfin_5xx.c
+++ b/drivers/serial/bfin_5xx.c
@@ -1190,6 +1190,10 @@ static __init void early_serial_putc(struct uart_port *port, int ch)
unsigned timeout = 0xffff;
struct bfin_serial_port *uart = (struct bfin_serial_port *)port;

+ /* We cannot cpu_relax() here as doing so on the BF561 relies
+ * on the per-cpu region being setup, and since this is early
+ * serial code, it may not yet be usable ...
+ */
while ((!(UART_GET_LSR(uart) & THRE)) && --timeout)
barrier();

--
1.5.6.3