Le 10/01/2022 à 07:14, Jason Wang a écrit :
在 2022/1/8 下午3:08, Christophe JAILLET 写道:
As stated in [1], dma_set_mask() with a 64-bit mask will never fail if
dev->dma_mask is non-NULL.
So, if it fails, the 32 bits case will also fail for the same reason.
I'd expect to be more verbose here. E.g I see dma_supported() who has a
brunch of checks need to be called if dma_mask is non-NULL.
Thanks
Hi,
If Christoph Hellwig's references ([1], [2]) are not enough, here is my
own analysis.
I put him in copy in case he has be better wording or explanation than me.
I've searched all dma_supported() function with grep
grep -r --include=*.[ch] \\.dma_supported * > dma_supported.txt
I've removed duplicates, then, I've audited audit all functions.
Short summary below.
Adding all this in the commit looks an overkill to me.
Maybe we can add a link to this mail if it looks good to you.
CJ
arch/arm/common/dmabounce.c: .dma_supported = dmabounce_dma_supported
==> Same as arm_dma_supported()
arch/arm/mm/dma-mapping.c: .dma_supported = arm_dma_supported
==> If a mask fails, smaller masks will fail as well.
arch/alpha/kernel/pci_iommu.c: .dma_supported = alpha_pci_supported
==> If a mask fails, smaller masks will fail as well.
arch/x86/kernel/amd_gart_64.c: .dma_supported = dma_direct_supported
==> Succeeds if >= 32 bits. If a mask fails, smaller masks will fail as
well.
arch/powerpc/kernel/dma-iommu.c: .dma_supported = dma_iommu_dma_supported
==> Tricky because of dma_iommu_bypass_supported(), but if a mask fails,
smaller masks will fail as well.
arch/powerpc/platforms/ps3/system-bus.c: .dma_supported = ps3_dma_supported
==> Succeeds if >= 32 bits
arch/powerpc/platforms/pseries/ibmebus.c: .dma_supported =
ibmebus_dma_supported
==> Succeeds if == 64 bits
arch/sparc/kernel/iommu.c: .dma_supported = dma_4u_supported
==> One corner case which accept only 31 bits
==> If a mask fails, smaller masks will fail as well
arch/sparc/kernel/pci_sun4v.c: .dma_supported = dma_4v_supported
==> Same as dma_4u_supported() above
arch/ia64/hp/common/sba_iommu.c: .dma_supported = sba_dma_supported
==> Succeeds if >= 32 bits
drivers/xen/swiotlb-xen.c: .dma_supported = xen_swiotlb_dma_supported
==> If a mask fails, smaller masks will fail as well.
drivers/parisc/ccio-dma.c: .dma_supported = ccio_dma_supported
==> Succeeds if >= 32 bits
drivers/parisc/sba_iommu.c: .dma_supported = sba_dma_supported
==> If a mask fails, smaller masks will fail as well.
kernel/dma/dummy.c: .dma_supported = dma_dummy_supported
==> Always fails, whatever the value of the mask
[1]: https://lore.kernel.org/linux-kernel/YL3vSPK5DXTNvgdx@xxxxxxxxxxxxx/
[2]: https://lore.kernel.org/kernel-janitors/YdK4IIFvi5O5eXHC@xxxxxxxxxxxxx/
