On 16/10/18 09:25, Hanna Hawa wrote:
Hi Robin,
On 10/15/2018 04:00 PM, Robin Murphy wrote:
Hi Hanna,
On 15/10/18 13:00, hannah@xxxxxxxxxxx wrote:
From: Hanna Hawa <hannah@xxxxxxxxxxx>
Due to erratum #582743, the Marvell Armada-AP806 can't access 64bit
to ARM SMMUv2 registers.
This patch split the writeq/readq to two accesses of writel/readl.
Note that separate writes/reads to 2 is not problem regards to
atomicity,
because the driver use the readq/writeq while initialize the SMMU,
report
for SMMU fault, and use spinlock in one case (iova_to_phys).
In general, this doesn't work. Here's what the SMMU spec says about
SMMU_CBn_TLBIVA, but others are similar:
"If SMMU_CBA2Rn.VA64 is one, then AArch64 format is selected. The
programmer should use 64 bit accesses to this register. If 32-bit
accesses are used then writes to the top 32 bits are ignored and writes
to the lower 32 bits are zero extended."
If your interconnect won't let 64-bit transactions through, then you
can't use AArch64 format at stage 1 at all, since there's no way to
invalidate entries with the correct ASID, and you'll have to restrict
stage 2 formats to at most 44-bit IOVAs in order for TLBIIPAS2{L} not to
invalidate the wrong thing.
Thanks for your suggestion.
To restrict the IOVAs i need to add another work-around to the driver to
limit the va_size, is that acceptable?
Yeah, constraining AArch64 stage 2 to 44 bits should just be a case of
adjusting smmu->ipa_size at probe time, but you'd still need to add the
writel()-based TLBI path to take advantage of it.
How big is the physical memory map on these SoCs? If everything fits
into 40 bits then I think you could get away with simply hiding the
SMMU_IDR2.PTFSv8 fields to sidestep the AArch64 formats altogether, and
everything else should fall out in the wash. Otherwise, you'll have to
just disable stage 1 support in addition to the stage 2 workaround as
above.
What the different in the driver between AARCH32_L & AARCH32_S?
AARCH32_L is the 3-level LPAE format, which gives you 32-bit
input/40-bit output at stage 1 and 40-bit input/40-bit output at stage
2. AARCH32_S is the legacy 2-level short-descriptor format which only
supports stage 1 and is limited to 32-bit output addresses - MMU-500
does support it, but you probably want to avoid it if possible ;)
Robin.
