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iommu: Do physical merging in iommu_map_sg() 

The original motivation for iommu_map_sg() was to give IOMMU drivers the
chance to map an IOVA-contiguous scatterlist as efficiently as they
could. It turns out that there isn't really much driver-specific
business involved there, so now that the default implementation is
mandatory let's just improve that - the main thing we're after is to use
larger pages wherever possible, and as long as domain->pgsize_bitmap
reflects reality, iommu_map() can already do that in a generic way. All
we need to do is detect physically-contiguous segments and batch them
into a single map operation, since whatever we do here is transparent to
our caller and not bound by any segment-length restrictions on the list
itself.

Speaking of efficiency, there's really very little point in duplicating
the checks that iommu_map() is going to do anyway, so those get cleared
up in the process.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
This commit is contained in:
Robin Murphy 2018-10-11 16:56:42 +01:00 committed by Joerg Roedel
parent 651022382c
commit 5d95f40e62
1 changed files with 20 additions and 21 deletions
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41
drivers/iommu/iommu.c
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@ -1712,33 +1712,32 @@ EXPORT_SYMBOL_GPL(iommu_unmap_fast);
size_t iommu_map_sg(struct iommu_domain *domain, unsigned long iova,
struct scatterlist *sg, unsigned int nents, int prot)
{
struct scatterlist *s;
size_t mapped = 0;
unsigned int i, min_pagesz;
size_t len = 0, mapped = 0;
phys_addr_t start;
unsigned int i = 0;
int ret;
if (unlikely(domain->pgsize_bitmap == 0UL))
return 0;
while (i <= nents) {
phys_addr_t s_phys = sg_phys(sg);
min_pagesz = 1 << __ffs(domain->pgsize_bitmap);
if (len && s_phys != start + len) {
ret = iommu_map(domain, iova + mapped, start, len, prot);
if (ret)
goto out_err;
for_each_sg(sg, s, nents, i) {
phys_addr_t phys = page_to_phys(sg_page(s)) + s->offset;
mapped += len;
len = 0;
}
/*
* We are mapping on IOMMU page boundaries, so offset within
* the page must be 0. However, the IOMMU may support pages
* smaller than PAGE_SIZE, so s->offset may still represent
* an offset of that boundary within the CPU page.
*/
if (!IS_ALIGNED(s->offset, min_pagesz))
goto out_err;
if (len) {
len += sg->length;
} else {
len = sg->length;
start = s_phys;
}
ret = iommu_map(domain, iova + mapped, phys, s->length, prot);
if (ret)
goto out_err;
mapped += s->length;
if (++i < nents)
sg = sg_next(sg);
}
return mapped;