Re: [ath9k-devel] [RFC] ath9k: Insert wmb before linking dma descriptors

["Luis R. Rodriguez" <lrodriguez@atheros.com>]

On Tue, Oct 05, 2010 at 06:17:44AM -0700, John W. Linville wrote:
> On Mon, Oct 04, 2010 at 10:55:08PM +0200, Björn Smedman wrote:
> > Hi all,
> > 
> > I've been looking at how ath9k does DMA and comparing with the
> > recommendations in the Linux kernel documentation for the DMA API[1]. To
> > me it looks like we risk setting up incorrect DMA descriptors on
> > platforms that can reorder writes because all data in the descriptor may
> > not be written to memory before the descriptor is linked into the DMA
> > chain.
> > 
> > The patch below attempts to remove this risk by inserting a write memory
> > barrier between where we set up a descriptor and where we add it to the 
> > DMA chain. My hope is that this may solve some of the harder chip lockups 
> > on MIPS but more testing is required to determine if it has this effect.
> > 
> > Any thoughts?
> > 
> > /Björn
> > 
> > 1. http://www.mjmwired.net/kernel/Documentation/DMA-API.txt
> 
> I think this seems OK...?

Felix is more familiar with this area so I'll let him chime with
his ACK/NACK.

  Luis