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

Hanjun Guo
2017-08-09T14:48:02Z

Hi Robin,

On 9 August 2017 at 19:50, Robin Murphy <robin.murphy@arm.com> wrote:
> Hi Hanjun,
>
> It's a nice surprise to see this already; one less thing for us to do :)

Glad to hear this patch set helps :)

>
> 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.

Hmm, since GSIV for control interrupts are SPI, those GSIVs should not
be zero, does it mean we need the code below?

if (smmu->event_gsiv && smmu->pri_gsiv && smmu->gerr_gsiv && smmu->sync_gsiv)
return -EINVAL;

This seems not consistent with the code for now (parsing
the SMMU GSIV for SMMU platform device).

>
>> + 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.

Good point, it will simplify the code, I will update this patch :)

Thanks
Hanjun