On Mon, Jun 17, 2024 at 03:39:45PM -0700, Nicolin Chen wrote:
> The IORT doc defines "Number of IDs" ("id_count" in the virt-acpi-build)
> to be "the number of IDs in the range minus one". Otherwise, Linux kernel
> reports "conflicting mapping for input ID" FW_BUG at the overlapped ID.
>
> Fixes: 42e0f050e3a5 ("hw/arm/virt-acpi-build: Add IORT support to bypass
> SMMUv3")
> Signed-off-by: Nicolin Chen <nicol...@nvidia.com>
> ---
> Changelog
> v2:
> * Moved "-1" to the same line of id_count calculation
> * Added "+1" to the next_range.input_base calculation
> v1:
> https://lore.kernel.org/all/20240613234802.828265-1-nicol...@nvidia.com/
>
> hw/arm/virt-acpi-build.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
> index c3ccfef026..631f2c6d04 100644
> --- a/hw/arm/virt-acpi-build.c
> +++ b/hw/arm/virt-acpi-build.c
> @@ -243,7 +243,8 @@ iort_host_bridges(Object *obj, void *opaque)
>
> AcpiIortIdMapping idmap = {
> .input_base = min_bus << 8,
> - .id_count = (max_bus - min_bus + 1) << 8,
> + /* id_count is the number of IDs in the range minus one */
> + .id_count = ((max_bus - min_bus + 1) << 8) - 1,
> };
> g_array_append_val(idmap_blob, idmap);
> }
> @@ -298,11 +299,13 @@ build_iort(GArray *table_data, BIOSLinker *linker,
> VirtMachineState *vms)
> idmap = &g_array_index(smmu_idmaps, AcpiIortIdMapping, i);
>
> if (next_range.input_base < idmap->input_base) {
> - next_range.id_count = idmap->input_base -
> next_range.input_base;
> + /* id_count is the number of IDs in the range minus one */
> + next_range.id_count = idmap->input_base -
> + next_range.input_base - 1;
> g_array_append_val(its_idmaps, next_range);
> }
>
> - next_range.input_base = idmap->input_base + idmap->id_count;
> + next_range.input_base = idmap->input_base + idmap->id_count + 1;
> }
All this has to be written in the way that actually refers to the
spec. id_count is nowhere in the spec and one has to know that
in the end this is used by build_iort_id_mapping to figure out
where this comes from. Not good.
I think the best way is to fix build_iort_id_mapping:
make it subtract 1 from id_count.
Then change text from "Number of IDs" to "Number of IDs - The number of IDs in
the range minus one"
You should also add the reference to IO Remapping Table document
near build_iort_id_mapping, it is currently unclear which table this
refers to.
Of couse this means the only correct use has to be tweaked so the change
to build_iort_id_mapping does not break it: 0xFFFF -> 0x10000 - but
that's good for readability, anyway.
> /* Append the last RC -> ITS ID mapping */
> --
> 2.43.0
