[PATCH 2/8] ARM: Implement read/write for ownership in theARMv6 DMA cache ops

[George G. Davis]

Hi,

On Fri, May 14, 2010 at 05:42:31PM +0100, Catalin Marinas wrote:
> On Fri, 2010-05-14 at 17:29 +0100, Catalin Marinas wrote:
> > What I think I missed in my patch (and didn't show up with a sata drive)
> > is the "sync" operations. The dma_sync_single_for_device(FROMDEVICE)
> > corrupts the existing buffer.
> > 
> > I'll post an updated patch shortly.
> 
> Actually I think the hunk that I posted earlier should be enough:

Um, apologies for the noise but I didn't understand if Ronen said
this resolved the e1000 problem or not.

Thanks!

--
Regards,
George

> 
> 
> diff --git a/arch/arm/mm/cache-v6.S b/arch/arm/mm/cache-v6.S
> index a4a6840..aa3ac32 100644
> --- a/arch/arm/mm/cache-v6.S
> +++ b/arch/arm/mm/cache-v6.S
> @@ -216,7 +216,8 @@ v6_dma_inv_range:
>  #endif
>  1:
>  #ifdef CONFIG_SMP
> -	str	r0, [r0]			@ write for ownership
> +	ldr	r2, [r0]			@ read for ownership
> +	str	r2, [r0]			@ write for ownership
>  #endif
>  #ifdef HARVARD_CACHE
>  	mcr	p15, 0, r0, c7, c6, 1		@ invalidate D line
> 
> 
> The dma_sync_single_for_cpu() eventually calls dmac_unmap_area() which
> on ARM11MPCore became a no-op. There is no problem since this function
> call is always preceded by a call to either dma_map_single() or
> dma_sync_single_to_device(), both of them calling dma_map_area() which
> does the cache invalidation.
> 
> With the patch above, v6_dma_inv_range() is no longer destructive so the
> transferred data to the SDRAM is preserved. We could even re-instate the
> v6_dma_unmap_area() function but for performance reasons I would leave
> it as a no-op.
> 
> Russell, are you ok with such change? Since you already applied the
> original patch as #6111, I will send an additional patch with this fix
> (I'm sending it directly to the patch system as I won't have access to
> my work PC this weekend. Feel free to apply or reject).
> 
> Thanks.
> 
> -- 
> Catalin