Messages in this thread | | | Subject | Re: [PATCH 02/18] Blackfin Serial Driver: use barrier instead of cpu_relax for Blackfin SMP like patch | From | gyang <> | Date | Tue, 10 Mar 2009 18:07:11 +0800 |
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On Fri, 2009-03-06 at 14:37 -0800, Andrew Morton wrote: > 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.
Do you mean remove cpu_relax(), and either not add barrier() here?
> > > > 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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