Re: [RFC/RFT] b43: Relax requirement for descriptors to be in the DMA zone

["Michael Büsch" <m@bues.ch>]

On Wed, 24 Aug 2011 17:02:52 -0500
Larry Finger <Larry.Finger@lwfinger.net> wrote:

> When 64-bit DMA was first used, there were problems with the
> BCM4311 (14e4:4311). The problem was "fixed" by using the GFP_DMA
> flag in the allocation of coherent ring descriptor memory.
> 
> The original problem is now believed to have been due to bugs in
> the 64-bit DMA implementation in the rest of the kernel, and that
> those bugs have been fixed. Accordingly, the requirement for the
> descriptors to be in the DMA zone is relaxed.
> 
> Bounce buffers are left in the DMA zone.
> 
> Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
> ---
> 
> John,
> 
> This material is for next.

John, please apply this even though it's marked RFC, unless somebody
objects in reasonable time, which I don't expect.

You can also add

Signed-off-by: Michael Buesch <m@bues.ch>

if you desire.

> Index: wireless-testing-new/drivers/net/wireless/b43/dma.c
> ===================================================================
> --- wireless-testing-new.orig/drivers/net/wireless/b43/dma.c
> +++ wireless-testing-new/drivers/net/wireless/b43/dma.c
> @@ -393,14 +393,7 @@ static int alloc_ringmemory(struct b43_d
>  	 * has shown that 4K is sufficient for the latter as long as the buffer
>  	 * does not cross an 8K boundary.
>  	 *
> -	 * For unknown reasons - possibly a hardware error - the BCM4311 rev
> -	 * 02, which uses 64-bit DMA, needs the ring buffer in very low memory,
> -	 * which accounts for the GFP_DMA flag below.
> -	 *
> -	 * The flags here must match the flags in free_ringmemory below!
>  	 */
> -	if (ring->type == B43_DMA_64BIT)
> -		flags |= GFP_DMA;
>  	ring->descbase = dma_alloc_coherent(ring->dev->dev->dma_dev,
>  					    B43_DMA_RINGMEMSIZE,
>  					    &(ring->dmabase), flags);
> 



-- 
Greetings, Michael.