Hi Will, > -----Original Message----- > From: Will Deacon [mailto:will.dea...@arm.com] > Sent: Monday, October 06, 2014 4:34 PM > To: Sethi Varun-B16395 > Cc: iommu@lists.linux-foundation.org; mitch...@codeaurora.org; > ohau...@codeaurora.org > Subject: Re: [RFC][PATCH 1/2] Introduce the IOMMU_DEVICE flag. > > Hi Varun, > > [adding the Qualcomm guys, as I have an open question below] > > On Mon, Oct 06, 2014 at 11:28:15AM +0100, Varun Sethi wrote: > > This is used for indicating device memory type for a DMA transaction. > > IOMMU driver would set up attributes indicationg access to device memory. > > > > Signed-off-by: Varun Sethi <varun.se...@freescale.com> > > --- > > include/linux/iommu.h | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/include/linux/iommu.h b/include/linux/iommu.h index > > 20f9a52..0599fe1 100644 > > --- a/include/linux/iommu.h > > +++ b/include/linux/iommu.h > > @@ -28,6 +28,7 @@ > > #define IOMMU_WRITE (1 << 1) > > #define IOMMU_CACHE (1 << 2) /* DMA cache coherency */ > > #define IOMMU_EXEC (1 << 3) > > +#define IOMMU_DEVICE (1 << 4) /* Indicates access to device memory > */ > > An alternative to this would be to make device-memory the default type for > !IOMMU_CACHE mappings (i.e. MAIR index 0). > > I'd value feedback either way; the argument comes down to whether we > should use normal non-cacheable or device-nGnRE as the default > (!IOMMU_CACHE) memory type. The latter is likely to be significantly slower, > but provides the ordering guarantees that you need for MSI delivery. > > If we do go down the route of adding a new IOMMU_* option, it probably > needs a better name (IOMMU_MMIO, for example). I think it would be better to have a separate flag for handling DMA access to device memory. There might be cases where we might want DMA accesses to be non cacheable. This may be required for preventing cache evictions (depending on the cache size).
-Varun _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
