Re: [RFC PATCH 3/4] ACPI: IORT: Skip SMMUv3 device ID map for two steps mappings

Robin Murphy
2017-08-09T11:50:47Z

Hi Hanjun,

It's a nice surprise to see this already; one less thing for us to do :)

On 09/08/17 11:53, Hanjun Guo wrote:
> From: Hanjun Guo <hanjun.guo@linaro.org>
>
> IORT revision C introduced SMMUv3 MSI support which adding a
> device ID mapping index in SMMUv3 sub table, to get the SMMUv3
> device ID mapping for the output ID (dev ID for ITS) and the
> link to which ITS.
>
> So if a platform supports SMMUv3 MSI for control interrupt,
> there will be a additional single map entry under SMMU, this
> will not introduce any difference for devices just use one
> step map to get its output ID and parent (ITS or SMMU), such
> as PCI/NC/PMCG ---> ITS or PCI/NC ---> SMMU, but we need to
> do the spcial handling for two steps map case such as
> PCI/NC--->SMMUv3--->ITS.
>
> Take a PCI hostbridge for example,
>
> |----------------------|
> | Root Complex Node |
> |----------------------|
> | map entry[x] |
> |----------------------|
> | id value |
> | output_reference |
> |---|------------------|
> |
> | |----------------------|
> |-->| SMMUv3 |
> |----------------------|
> | SMMU dev ID |
> | mapping index 0 |
> |----------------------|
> | map entry[0] |
> |----------------------|
> | id value |
> | output_reference-----------> ITS 1 (SMMU MSI domain)
> |----------------------|
> | map entry[1] |
> |----------------------|
> | id value |
> | output_reference-----------> ITS 2 (PCI MSI domain)
> |----------------------|
>
> When the SMMU dev ID mapping index is 0, there is entry[0]
> to map to a ITS, we need to skip that map entry for PCI
> or NC (named component), or we may get the wrong ITS parent.
>
> For now we have two APIs for ID mapping, iort_node_map_id()
> and iort_node_map_platform_id(), and iort_node_map_id() is
> used for optional two steps mapping, so we just need to
> skip the map entry in iort_node_map_id() for non-SMMUv3
> devices.
>
> Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>
> ---
> drivers/acpi/arm64/iort.c | 37 ++++++++++++++++++++++++++++++++++++-
> 1 file changed, 36 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c
> index 32bd4a4..9439f02 100644
> --- a/drivers/acpi/arm64/iort.c
> +++ b/drivers/acpi/arm64/iort.c
> @@ -366,6 +366,28 @@ struct acpi_iort_node *iort_node_get_id(struct acpi_iort_node *node,
> return NULL;
> }
>
> +static int iort_get_smmu_v3_id_mapping_index(struct acpi_iort_node *node,
> + u32 *index)
> +{
> + struct acpi_iort_smmu_v3 *smmu;
> +
> + /*
> + * SMMUv3 dev ID mapping index was introdueced in revision 1
> + * table, not avaible in revision 0
> + */
> + if (node->revision < 1)
> + return -EINVAL;
> +
> + smmu = (struct acpi_iort_smmu_v3 *)node->node_data;
> + /* if any of the gsi for control interrupts is not 0, ignore the MSI */

IORT says "If all the SMMU control interrupts are GSIV based, this
field is ignored" - not "any". There doesn't seem to be any reason to
disallow a mixture of MSIs and GSIs.

> + if (smmu->event_gsiv || smmu->pri_gsiv || smmu->gerr_gsiv
> + || smmu->sync_gsiv)
> + return -EINVAL;
> +
> + *index = smmu->id_mapping_index;
> + return 0;
> +}
> +
> static struct acpi_iort_node *iort_node_map_id(struct acpi_iort_node *node,
> u32 id_in, u32 *id_out,
> u8 type_mask)
> @@ -375,7 +397,9 @@ static struct acpi_iort_node *iort_node_map_id(struct acpi_iort_node *node,
> /* Parse the ID mapping tree to find specified node type */
> while (node) {
> struct acpi_iort_id_mapping *map;
> - int i;
> + int i, ret = -EINVAL;
> + /* big enough for an invalid id index in practical */
> + u32 index = U32_MAX;
>
> if (IORT_TYPE_MASK(node->type) & type_mask) {
> if (id_out)
> @@ -396,8 +420,19 @@ static struct acpi_iort_node *iort_node_map_id(struct acpi_iort_node *node,
> goto fail_map;
> }
>
> + /*
> + * we need to get SMMUv3 dev ID mapping index and skip its
> + * associated ID map for single mapping cases.
> + */
> + if (node->type == ACPI_IORT_NODE_SMMU_V3)
> + ret = iort_get_smmu_v3_id_mapping_index(node, &index);
> +
> /* Do the ID translation */
> for (i = 0; i < node->mapping_count; i++, map++) {
> + /* if it's a SMMUv3 device id mapping index, skip it */
> + if (!ret && i == index)

Given that i is an int anyway, there doesn't seem to be much need for
the ret dance - iort_get_smmu_v3_id_mapping_index() could just return
the index/error value as an int directly. You can rely on (i == index)
being false if index is negative, because for node->mapping_count to
overflow INT_MAX the IORT would have to be over 40GB in size, which is
definitely impossible.

Robin.

> + continue;
> +
> if (!iort_id_map(map, node->type, id, &id))
> break;
> }
>