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

Andrew Morton
2009-03-06T22:39:41Z

On Fri, 6 Mar 2009 14:42:48 +0800
Bryan Wu <cooloney@kernel.org> wrote:

> 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();

Again: this is blackfin core breakage.