From: Andrew Morton <akpm@linux-foundation.org>
To: Mike Frysinger <vapier.adi@gmail.com>
Cc: gyang <graf.yang@analog.com>, Bryan Wu <cooloney@kernel.org>,
alan@lxorguk.ukuu.org.uk, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 02/18] Blackfin Serial Driver: use barrier instead of cpu_relax for Blackfin SMP like patch
Date: Tue, 10 Mar 2009 09:48:10 -0700 [thread overview]
Message-ID: <20090310094810.2ffe1f63.akpm@linux-foundation.org> (raw)
In-Reply-To: <8bd0f97a0903100325k6cbcf73ek8e5f3723b2c4bb0a@mail.gmail.com>
On Tue, 10 Mar 2009 06:25:08 -0400 Mike Frysinger <vapier.adi@gmail.com> wrote:
> On Tue, Mar 10, 2009 at 06:07, gyang wrote:
> > 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?
>
> afaik, early printk all runs before SMP is setup, so having it be a
> 100% busy wait is fine
No, blackfin is busted, please fix this bug in blackfin core.
What happens if core kernel code decides to run cpu_relax() prior to
initialising per-cpu data?
next prev parent reply other threads:[~2009-03-10 16:54 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-03-06 6:42 [PATCH 00/18] Blackfin Serial Driver bug fixing and update Bryan Wu
2009-03-06 6:42 ` [PATCH 01/18] Blackfin Serial Driver: Add a debug function to serial driver Bryan Wu
2009-03-06 22:37 ` Andrew Morton
2009-03-06 6:42 ` [PATCH 02/18] Blackfin Serial Driver: use barrier instead of cpu_relax for Blackfin SMP like patch Bryan Wu
2009-03-06 22:37 ` Andrew Morton
2009-03-10 10:07 ` gyang
2009-03-10 10:25 ` Mike Frysinger
2009-03-10 16:48 ` Andrew Morton [this message]
2009-03-11 9:50 ` graff yang
2009-03-11 16:48 ` Andrew Morton
2009-03-06 6:42 ` [PATCH 03/18] Blackfin Serial Driver: fix a in dma circle rx buffer handling Bryan Wu
2009-03-06 22:38 ` Andrew Morton
2009-03-06 6:42 ` [PATCH 04/18] Blackfin Serial Driver: Change hardware flowcontrol from poll to interrupt driven Bryan Wu
2009-03-06 22:38 ` Andrew Morton
2009-03-06 22:49 ` Mike Frysinger
2009-03-06 23:00 ` Andrew Morton
2009-03-06 6:42 ` [PATCH 05/18] Blackfin Serial Driver: fix bug - serial port transfer big file from host to target would have more lines Bryan Wu
2009-03-06 22:38 ` Andrew Morton
2009-03-06 6:42 ` [PATCH 06/18] Blackfin Serial Driver: explain why we cannot cpu_relax() in early serial code Bryan Wu
2009-03-06 22:38 ` Andrew Morton
2009-03-06 6:42 ` [PATCH 07/18] Blackfin Serial Driver: BF538/9 Linux kernel Support Bryan Wu
2009-03-06 6:42 ` [PATCH 08/18] Blackfin Serial Driver: use "unsigned long" for flags with irq functions rather than "int" Bryan Wu
2009-03-06 6:42 ` [PATCH 09/18] Blackfin Serial Driver: irq funcs take an unsigned long for flags Bryan Wu
2009-03-06 6:42 ` [PATCH 10/18] Blackfin Serial Driver: fix compile error in PIO mode Bryan Wu
2009-03-06 6:42 ` [PATCH 11/18] Blackfin Serial Driver: update KGDB UART config name Bryan Wu
2009-03-06 6:42 ` [PATCH 12/18] Blackfin Serial Driver: fix building when debug is enabled but serial console is disabled Bryan Wu
2009-03-06 6:42 ` [PATCH 13/18] Blackfin Serial Driver: depend on KGDB_SERIAL_CONSOLE being set to N Bryan Wu
2009-03-06 6:42 ` [PATCH 14/18] Blackfin Serial Driver: use the DLAB macro to hide variant differences Bryan Wu
2009-03-06 22:38 ` Andrew Morton
2009-03-06 22:41 ` Mike Frysinger
2009-03-06 6:42 ` [PATCH 15/18] Blackfin Serial Driver: merge the upstream adeos/xenomai Bryan Wu
2009-03-06 22:38 ` Andrew Morton
2009-03-06 22:43 ` Mike Frysinger
2009-03-06 6:42 ` [PATCH 16/18] Blackfin Serial Driver: fix bug - up arrow key works abnormal for bf561 ezkit board Bryan Wu
2009-03-06 6:42 ` [PATCH 17/18] Blackfin Serial Driver: Fix bug - Enable hardware based CTS and RTS for bf548 Bryan Wu
2009-03-06 22:38 ` Andrew Morton
2009-03-06 6:43 ` [PATCH 18/18] Blackfin Serial Driver: update path to gpio header Bryan Wu
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