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

[Robin Murphy]

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 at 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 at 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;
>  		}
>