On Mon, 5 Oct 2020 16:16:32 +0100 Steven Price <[email protected]> wrote:
> On 05/10/2020 15:50, Boris Brezillon wrote: > > On Tue, 22 Sep 2020 15:16:48 +0100 > > Robin Murphy <[email protected]> wrote: > > > >> Midgard GPUs have ACE-Lite master interfaces which allows systems to > >> integrate them in an I/O-coherent manner. It seems that from the GPU's > >> viewpoint, the rest of the system is its outer shareable domain, and so > >> even when snoop signals are wired up, they are only emitted for outer > >> shareable accesses. As such, setting the TTBR_SHARE_OUTER bit does > >> indeed get coherent pagetable walks working nicely for the coherent > >> T620 in the Arm Juno SoC. > >> > >> Reviewed-by: Steven Price <[email protected]> > >> Tested-by: Neil Armstrong <[email protected]> > >> Signed-off-by: Robin Murphy <[email protected]> > >> --- > >> drivers/iommu/io-pgtable-arm.c | 11 ++++++++++- > >> 1 file changed, 10 insertions(+), 1 deletion(-) > >> > >> diff --git a/drivers/iommu/io-pgtable-arm.c > >> b/drivers/iommu/io-pgtable-arm.c > >> index dc7bcf858b6d..b4072a18e45d 100644 > >> --- a/drivers/iommu/io-pgtable-arm.c > >> +++ b/drivers/iommu/io-pgtable-arm.c > >> @@ -440,7 +440,13 @@ static arm_lpae_iopte arm_lpae_prot_to_pte(struct > >> arm_lpae_io_pgtable *data, > >> << ARM_LPAE_PTE_ATTRINDX_SHIFT); > >> } > >> > >> - if (prot & IOMMU_CACHE) > >> + /* > >> + * Also Mali has its own notions of shareability wherein its Inner > >> + * domain covers the cores within the GPU, and its Outer domain is > >> + * "outside the GPU" (i.e. either the Inner or System domain in CPU > >> + * terms, depending on coherency). > >> + */ > >> + if (prot & IOMMU_CACHE && data->iop.fmt != ARM_MALI_LPAE) > >> pte |= ARM_LPAE_PTE_SH_IS; > >> else > >> pte |= ARM_LPAE_PTE_SH_OS; > > > > Actually, it still doesn't work on s922x :-/. For it to work I > > correctly, I need to drop the outer shareable flag here. > > The logic here does seem a bit odd. Originally it was: > > IOMMU_CACHE -> Inner shared (value 3) > !IOMMU_CACHE -> Outer shared (value 2) > > For Mali we're forcing everything to the second option. But Mali being > Mali doesn't do things the same as LPAE, so for Mali we have: > > 0 - not shared > 1 - reserved > 2 - inner(*) and outer shareable > 3 - inner shareable only > > (*) where "inner" means internal to the GPU, and "outer" means shared > with the CPU "inner". Very confusing! > > So originally we had: > IOMMU_CACHE -> not shared with CPU (only internally in the GPU) > !IOMMU_CACHE -> shared with CPU > > The change above gets us to "always shared", dropping the SH_OS bit > would get us to not even shareable between cores (which doesn't sound > like what we want). Thanks for this explanation. > > It's not at all clear to me why the change helps, but I suspect we want > at least "inner" shareable. Right. Looks like all this was caused by a bad conflict resolution during a rebase. Sorry for the noise :-/. _______________________________________________ iommu mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/iommu
