Messages in this thread | | | Date | Fri, 6 Mar 2009 14:37:56 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH 02/18] Blackfin Serial Driver: use barrier instead of cpu_relax for Blackfin SMP like patch |
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On Fri, 6 Mar 2009 14:42:44 +0800 Bryan Wu <cooloney@kernel.org> wrote:
> From: Graf Yang <graf.yang@analog.com> > > We are making a SMP like patch to blackfin, cpu_relax() is replaced by a > data cache flush function which will count it to a per-cpu counter. > If this serial function is called too early, the per-cpu data area have > not been initialized, this call will cause crash.
That's a bug in blackfin architecture support. The kernel should be able to call cpu_relax() at any time, surely. It's a very low-level and simple thing.
> So we'd like to use barrier() instead of cpu_relax(). >
barrier() is purely a compiler concept. We might as well just remove the cpu_relax() altogether.
> drivers/serial/bfin_5xx.c | 3 ++- > 1 files changed, 2 insertions(+), 1 deletions(-) > > diff --git a/drivers/serial/bfin_5xx.c b/drivers/serial/bfin_5xx.c > index 52ccc27..350bfc4 100644 > --- a/drivers/serial/bfin_5xx.c > +++ b/drivers/serial/bfin_5xx.c > @@ -1129,7 +1129,8 @@ static __init void early_serial_putc(struct uart_port *port, int ch) > struct bfin_serial_port *uart = (struct bfin_serial_port *)port; > > while ((!(UART_GET_LSR(uart) & THRE)) && --timeout) > - cpu_relax(); > + barrier(); > + > UART_PUT_CHAR(uart, ch); > }
I grumpily queued this, but it seems all wrong.
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