[PATCH 1/2] iommu/mediatek: select ARM_DMA_USE_IOMMU
arnd at arndb.de
Mon Feb 29 02:53:46 PST 2016
On Monday 29 February 2016 10:37:40 Robin Murphy wrote:
> Hi Arnd,
> On 29/02/16 09:19, Arnd Bergmann wrote:
> > The newly added Mediatek IOMMU driver uses the IOMMU_DMA infrastructure,
> > but unlike other such drivers, it does not select 'ARM_DMA_USE_IOMMU',
> > which is a prerequisite, leading to a link error:
> > warning: (MTK_IOMMU) selects IOMMU_DMA which has unmet direct dependencies (IOMMU_SUPPORT && NEED_SG_DMA_LENGTH)
> Going off on a tangent, is it actually right for that to depend on a
> NEED_* symbol, or should that really be a select instead?
ARM_DMA_USE_IOMMU gets this right, it selects NEED_SG_DMA_LENGTH as it
actually needs it.
The IOMMU_DMA symbol is a bit strange, and the dependency can probably
get dropped altogether, but at least here it told us what went wrong.
> > drivers/iommu/built-in.o: In function `iommu_put_dma_cookie':
> > mtk_iommu.c:(.text+0x11fe): undefined reference to `put_iova_domain'
> > drivers/iommu/built-in.o: In function `iommu_dma_init_domain':
> > mtk_iommu.c:(.text+0x1316): undefined reference to `init_iova_domain'
> > drivers/iommu/built-in.o: In function `__iommu_dma_unmap':
> > mtk_iommu.c:(.text+0x1380): undefined reference to `find_iova'
> > This adds the same select that the other drivers have. On a related
> > note, I wonder if we should just always select ARM_DMA_USE_IOMMU
> > whenever any IOMMU driver is enabled. Are there any cases where
> > we would enable an IOMMU but not use it?
> You could use one solely for VFIO without caring about DMA ops - I think
> that's mostly how ARM SMMUs are being used in practice at the moment -
> but DMA-focused 'media' IOMMUs vastly outnumber 'virtualisation' IOMMUs
> on ARM, so it would probably make sense. We already have the equivalent
> "select IOMMU_DMA if IOMMU_SUPPORT" on arm64.
> > Signed-off-by: Arnd Bergmann <arnd at arndb.de>
> > Fixes: 0df4fabe208d ("iommu/mediatek: Add mt8173 IOMMU driver")
> > ---
> > drivers/iommu/Kconfig | 1 +
> > 1 file changed, 1 insertion(+)
> > diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> > index b325954cf8f8..ea0998921702 100644
> > --- a/drivers/iommu/Kconfig
> > +++ b/drivers/iommu/Kconfig
> > @@ -341,6 +341,7 @@ config MTK_IOMMU
> > bool "MTK IOMMU Support"
> > depends on ARM || ARM64
> > depends on ARCH_MEDIATEK || COMPILE_TEST
> > + select ARM_DMA_USE_IOMMU
> If going down this route, I'd be inclined to add an "if ARM" there, just
> for clarity.
That would run into the NEED_SG_DMA_LENGTH problem on other architectures
that don't already set it, right?
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