Messages in this thread | | | From | Arnd Bergmann <> | Subject | Re: [PATCH 1/2] iommu/mediatek: select ARM_DMA_USE_IOMMU | Date | Mon, 29 Feb 2016 11:53:46 +0100 |
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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.
Ok.
> > Signed-off-by: Arnd Bergmann <arnd@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?
Arnd
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