On 2023/8/15 1:30, Jason Gunthorpe wrote:
On Mon, Aug 14, 2023 at 04:43:23PM +0800, Baolu Lu wrote:
This is on github:https://github.com/jgunthorpe/linux/commits/iommu_all_defdom
It seems that after this series, all ARM iommu drivers are able to
support the IDENTITY default domain, hence perhaps we can remove below
code?
Yes, but this code is still used
If I remember it correctly, the background of this part of code is
that some arm drivers didn't support IDENTITY domain, so fall back to
DMA domain if IDENTITY domain allocation fails.
Not quite..
if (req_type)
return __iommu_group_alloc_default_domain(group, req_type);
req_type == 0 can still happen because it depends on what
def_domain_type returns, which is still 0 in alot of cases
/* The driver gave no guidance on what type to use, try the default */
dom = __iommu_group_alloc_default_domain(group, iommu_def_domain_type);
if (dom)
return dom;
So we try the default which might be IDENTITY/DMA/DMA_FQ - still have
to do this.
/* Otherwise IDENTITY and DMA_FQ defaults will try DMA */
if (iommu_def_domain_type == IOMMU_DOMAIN_DMA)
return NULL;
dom = __iommu_group_alloc_default_domain(group, IOMMU_DOMAIN_DMA);
if (!dom)
return NULL;
pr_warn("Failed to allocate default IOMMU domain of type %u for group %s - Falling back to IOMMU_DOMAIN_DMA",
iommu_def_domain_type, group->name);
And this hunk is primarily a fallback in case the DMA_FQ didn't
work. Then we try normal DMA.
That it also protected against not implementing IDENTITY is a side
effect, so I think we have to keep all of this still.
Okay, fair enough. Thanks for the explanation.
Best regards,
baolu
