linux-kernel - Re: [PATCH] gpu: host1x: Use direct DMA with IOMMU API usage

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Message-ID: <20190207085129.GB8741@ulmo>
Date:   Thu, 7 Feb 2019 09:51:31 +0100
From:   Thierry Reding <treding@...dia.com>
To:     Guenter Roeck <linux@...ck-us.net>
CC:     <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gpu: host1x: Use direct DMA with IOMMU API usage

On Wed, Feb 06, 2019 at 02:08:33PM -0800, Guenter Roeck wrote:
> On Fri, Feb 01, 2019 at 02:28:26PM +0100, Thierry Reding wrote:
> > If we use the IOMMU API directly to map buffers into host1x' IOVA space,
> > we must make sure that the DMA API doesn't already set up a mapping, or
> > else translation will fail.
> > 
> > The direct DMA API allows us to allocate memory that will not be mapped
> > through an IOMMU automatically.
> > 
> > Reviewed-by: Dmitry Osipenko <digetx@...il.com>
> > Signed-off-by: Thierry Reding <treding@...dia.com>
> 
> arm64:defconfig:
> 
> ERROR: "dma_direct_free" [drivers/gpu/host1x/host1x.ko] undefined!
> ERROR: "dma_direct_alloc" [drivers/gpu/host1x/host1x.ko] undefined!

Hi Guenter,

I sent out a fix to export dma_direct_alloc() and dma_direct_free() but
Christoph preferred not to merge that, so I'm currently working on a
different solution for this. I hope to have a fix for this by the end of
the day, but if not I'll back out the above commit.

Thanks,
Thierry

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