On 2021-06-16 12:28, Sai Prakash Ranjan wrote:
Hi Robin,
On 2021-06-15 19:23, Robin Murphy wrote:
On 2021-06-15 12:51, Sai Prakash Ranjan wrote:
<snip>...
Hi @Robin, from these discussions it seems they are not ok with the
change
for all SoC vendor implementations and do not have any data on such
impact.
As I mentioned above, on QCOM platforms we do have several
optimizations in HW
for TLBIs and would like to make use of it and reduce the unmap
latency.
What do you think, should this be made implementation specific?
Yes, it sounds like there's enough uncertainty for now that this needs
to be an opt-in feature. However, I still think that non-strict mode
could use it generically, since that's all about over-invalidating to
save time on individual unmaps - and relatively non-deterministic -
already.
So maybe we have a second set of iommu_flush_ops, or just a flag
somewhere to control the tlb_flush_walk functions internally, and the
choice can be made in the iommu_get_dma_strict() test, but also forced
on all the time by your init_context hook. What do you reckon?
Sounds good to me. Since you mentioned non-strict mode using it
generically,
can't we just set tlb_flush_all() in io_pgtable_tlb_flush_walk() like
below
based on quirk so that we don't need to add any check in
iommu_get_dma_strict()
and just force the new flush_ops in init_context hook?
if (iop->cfg.quirks & IO_PGTABLE_QUIRK_NON_STRICT) {
iop->cfg.tlb->tlb_flush_all(iop->cookie);
return;
}
Instead of flush_ops in init_context hook, perhaps a io_pgtable quirk
since this
is related to tlb, probably a bad name but IO_PGTABLE_QUIRK_TLB_INV
which will be
set in init_context impl hook and the prev condition in
io_pgtable_tlb_flush_walk()
becomes something like below. Seems very minimal and neat instead of
poking into
tlb_flush_walk functions or touching dma strict with some flag?
if (iop->cfg.quirks & IO_PGTABLE_QUIRK_NON_STRICT ||
iop->cfg.quirks & IO_PGTABLE_QUIRK_TLB_INV) {
iop->cfg.tlb->tlb_flush_all(iop->cookie);
return;
}
Thanks,
Sai
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