From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Stefan Richter <stefanr@s5r6.in-berlin.de>
Cc: linux-kernel@vger.kernel.org
Subject: Re: memory barriers and dma_sync_single_for_*
Date: Sun, 09 Jul 2006 16:46:27 +0100 [thread overview]
Message-ID: <1152459987.27368.64.camel@localhost.localdomain> (raw)
In-Reply-To: <44B11861.3070703@s5r6.in-berlin.de>
Ar Sul, 2006-07-09 am 16:53 +0200, ysgrifennodd Stefan Richter:
> My question: Do I need wmb() within the following code?
>
> dma_sync_single_for_cpu(..., DMA_TO_DEVICE);
> area->a = new_val_a;
> wmb(); /* necessary? */
> area->b = new_val_b;
Yes. Otherwise on some processors the I/O may be re-ordered
> dma_sync_single_for_device(..., DMA_TO_DEVICE);
>
> Or are all changes to the area hidden from the device between
> dma_sync_single_for_cpu and _for_device, thereby making the write order
> a non-issue? Thanks,
Depends on the processor and setup. On x86-32 for example dma_sync_.. is
generally a NOP. In other environments nothing will be visible until the
sync.
Alan
prev parent reply other threads:[~2006-07-09 15:28 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-07-09 14:53 Stefan Richter
2006-07-09 15:46 ` Alan Cox [this message]
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