[PATCH 09/30] blackfin: Explain why we cannot cpu_relax() in early serial code

Alan Cox
2009-03-24T14:06:40Z

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

Signed-off-by: Mike Frysinger <vapier.adi@gmail.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
Signed-off-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
---

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 d46d764..c7c0c1b 100644
--- a/drivers/serial/bfin_5xx.c
+++ b/drivers/serial/bfin_5xx.c
@@ -1127,6 +1127,10 @@ 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();