linux-kernel - Re: [Xen-devel] [PATCH 1/1] XEN: Use correct masking in xen_swiotlb_alloc

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Message-ID: <20120905143318.GA6908@phenom.dumpdata.com>
Date:	Wed, 5 Sep 2012 10:33:18 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Stefano Panella <stefano.panella@...rix.com>
Cc:	David Vrabel <david.vrabel@...rix.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>
Subject: Re: [Xen-devel] [PATCH 1/1] XEN: Use correct masking in
 xen_swiotlb_alloc_coherent.

On Tue, Sep 04, 2012 at 03:07:42PM +0100, Stefano Panella wrote:
> On 08/31/2012 05:40 PM, Konrad Rzeszutek Wilk wrote:
> >On Fri, Aug 31, 2012 at 01:47:05PM +0100, David Vrabel wrote:
> >>On 31/08/12 10:57, Stefano Panella wrote:
> >>>When running 32-bit pvops-dom0 and a driver tries to allocate a coherent
> >>>DMA-memory the xen swiotlb-implementation returned memory beyond 4GB.
> >>>
> >>>This caused for example not working sound on a system with 4 GB and a 64-bit
> >>>compatible sound-card with sets the DMA-mask to 64bit.
> >>>
> >>>On bare-metal and the forward-ported xen-dom0 patches from OpenSuse a coherent
> >>>DMA-memory is always allocated inside the 32-bit address-range by calling
> >>>dma_alloc_coherent_mask.
> >>We should have the same behaviour under Xen as bare metal so:
> >>
> >>Acked-By: David Vrabel <david.vrabel@...rix.com>
> >>
> >>This does limit the DMA mask to 32-bits by passing it through an
> >>unsigned long, which seems a bit sneaky...
> >so is the issue that we are not casting it from 'u64' to 'u32'
> >(unsigned long) on 32-bit?
> 
> Yes. I do not completely understand why but I think on 32-bit kernel we need to cast dma_mask to u32. This is done automatically using dma_alloc_coherent_mask()

OK, patch applied. I altered the git commit description a bit and
changed the author to  Ronny Hegewald <ronny.hegewald@...ine.de>.

Also added it on stable@...r.kernel.org

Thanks for tracking this down.
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