From: Ralf Baechle <ralf@linux-mips.org>
To: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Cc: Marco Braga <marco.braga@gmail.com>,
Domen Puncer <domen.puncer@telargo.com>,
linux-mips@linux-mips.org
Subject: Re: Trouble with sound/mips/au1x00.c AC97 driver
Date: Tue, 13 Mar 2007 00:43:15 +0000 [thread overview]
Message-ID: <20070313004315.GA26119@linux-mips.org> (raw)
In-Reply-To: <45F57328.8000606@ru.mvista.com>
On Mon, Mar 12, 2007 at 06:35:04PM +0300, Sergei Shtylyov wrote:
> >>It might be ignorance on my part, but aren't au_sync()'s needed here?
>
> >My ignorance too.. What's au_sync()? Something to writeback/invalidate the
> >cache?
>
> It's "memory barrier" (SYNC instruction).
For the general MIPS case (Alchemy may provide guarantees I don't know of)
a SYNC instruction is not sufficient to ensure that a write has actually
been reached by the device. It may just like on PCI take a read from the
same device again:
au1000->ac97_ioport->config = AC97C_SG | AC97C_SYNC;
au1000->ac97_ioport->config;
udelay(100);
au1000->ac97_ioport->config = 0x0;
to ensure that all preceding write have actually made it. That also means
that any use of the SYNC instruction may well be just an attempt to paper
over a bug.
Ralf
next prev parent reply other threads:[~2007-03-13 0:46 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-03-07 10:49 Trouble with sound/mips/au1x00.c AC97 driver Freddy Spierenburg
2007-03-09 7:22 ` Marco Braga
2007-03-09 10:33 ` Freddy Spierenburg
2007-03-10 13:20 ` Marco Braga
[not found] ` <45F350E9.3020208@cooper-street.com>
[not found] ` <d459bb380703120157wb3dde00p4c232e300e82fd3d@mail.gmail.com>
2007-03-12 9:59 ` Marco Braga
2007-03-12 10:39 ` Domen Puncer
2007-03-12 13:09 ` Marco Braga
2007-03-12 15:35 ` Sergei Shtylyov
2007-03-13 0:43 ` Ralf Baechle [this message]
2007-03-13 1:00 ` Andrew Dyer
2007-03-13 1:09 ` Ralf Baechle
2007-03-13 8:44 ` Marco Braga
[not found] ` <45F5DC73.9060004@cooper-street.com>
[not found] ` <d459bb380703130143w7c98e1cchdbdae6cb9a7ac7ce@mail.gmail.com>
[not found] ` <45F71FFD.202@cooper-street.com>
2007-03-13 23:12 ` Marco Braga
2007-03-15 8:04 ` Marco Braga
2007-04-16 14:47 ` Freddy Spierenburg
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