On 21/04/16 17:30, Will Deacon wrote:
Hi Robin,
On Wed, Apr 13, 2016 at 06:13:02PM +0100, Robin Murphy wrote:
The way the driver currently forces an AArch32 or AArch64 context format
based on the kernel config and SMMU architecture version is suboptimal,
in that it makes it very hard to support oddball mix-and-match cases
like the SMMUv1 64KB supplement, or situations where the reduced table
depth of an AArch32 short descriptor context may be desirable under an
AArch64 kernel. It also only happens to work on current implementations
which do support all the relevant formats.
Introduce an explicit notion of context format, so we can manage that
independently and get rid of the inflexible #ifdeffery.
Thanks for doing all of this! One comment on the page size stuff:
+ if (IS_ENABLED(CONFIG_64BIT) || cfg->fmt == ARM_SMMU_CTX_FMT_NONE) {
+ switch (PAGE_SIZE) {
+ case SZ_64K:
+ if (smmu->features & ARM_SMMU_FEAT_FMT_AARCH64_64K) {
+ cfg->fmt = ARM_SMMU_CTX_FMT_AARCH64;
+ break;
+ } /* else fall through */
+ case SZ_16K:
+ if (smmu->features & ARM_SMMU_FEAT_FMT_AARCH64_16K) {
+ cfg->fmt = ARM_SMMU_CTX_FMT_AARCH64;
+ break;
+ } /* else fall through */
+ case SZ_4K:
+ if (smmu->features & ARM_SMMU_FEAT_FMT_AARCH64_4K)
+ cfg->fmt = ARM_SMMU_CTX_FMT_AARCH64;
+ }
+ }
The io-pgtable code (arm_lpae_restrict_pgsizes) already does something
*very* similar to this, using the pgsize_bitmap as input. Can you not
just choose the ARM_SMMU_CTX_FMT_AARCH64 here and set the pgsize_bitmap
to represent all page sizes supported by the hardware? That way, you should
end up with the best option coming back from the pgtable code (I do this
in the v3 driver, fwiw).
It took a while to come back to me, but the problem is that we can't
call alloc_io_pgtable_ops(fmt...) before choosing either ARM_64_LPAE_Sx
or ARM_32_LPAE_Sx for fmt, but if we commit to 64-bit we'll get stuck
later without the possibility of falling back to AArch32 if it turns out
we don't have a viable AArch64 granule. Plus we'd have to remove the
LPAE page sizes from the bitmap beforehand in the case we don't support
AARCH64_4K lest we end up with a phantom format the hardware doesn't
actually do, and it all starts getting rather horrible...
Robin.
Will
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