Re: [PATCH v4 3/3] arm,smmu: add support for generic DT bindings. Implement add_device and dt_xlate.

[Julien Grall <julien@xen.org>]

Hi Stefano,

On 17/07/2021 00:59, Stefano Stabellini wrote:
> From: Brian Woods <brian.woods@xilinx.com>
> 
> For the legacy path, arm_smmu_dt_add_device_legacy is called by
> register_smmu_master scanning mmu-masters (a fwspec entry is also
> created.) For the generic path, arm_smmu_dt_add_device_generic gets
> called instead. Then, arm_smmu_dt_add_device_generic calls
> arm_smmu_dt_add_device_legacy afterwards, shared with the legacy path.
> This way most of the low level implementation is shared between the two
> paths.
> 
> If both legacy bindings and generic bindings are present in device tree,
> the legacy bindings are the ones that are used. That's because
> mmu-masters is parsed by
> xen/drivers/passthrough/arm/smmu.c:arm_smmu_device_dt_probe which is
> called by arm_smmu_dt_init. It happens very early. iommus is parsed by
> xen/drivers/passthrough/device_tree.c:iommu_add_dt_device which is
> called by xen/arch/arm/domain_build.c:handle_device and happens
> afterwards.
> 
> arm_smmu_dt_xlate_generic is a verbatim copy from Linux
> (drivers/iommu/arm/arm-smmu/arm-smmu.c:arm_smmu_of_xlate, version
> v5.10).
> 
> A workaround was introduced by cf4af9d6d6c (xen/arm: boot with device
> trees with "mmu-masters" and "iommus") because the SMMU driver only
> supported the legacy bindings. Remove it now.
> 
> Signed-off-by: Brian Woods <brian.woods@xilinx.com>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>
> Reviewed-by: Rahul Singh <rahul.singh@arm.com>

Acked-by: Julien Grall <jgrall@amazon.com>

Cheers,

> ---
> Changes in v4:
> - improve indentation
> - improve commit message
> ---
>   xen/drivers/passthrough/arm/smmu.c    | 40 ++++++++++++++++++++++++++-
>   xen/drivers/passthrough/device_tree.c | 17 +-----------
>   2 files changed, 40 insertions(+), 17 deletions(-)
> 
> diff --git a/xen/drivers/passthrough/arm/smmu.c b/xen/drivers/passthrough/arm/smmu.c
> index 252e8c1680..a065ba3f4e 100644
> --- a/xen/drivers/passthrough/arm/smmu.c
> +++ b/xen/drivers/passthrough/arm/smmu.c
> @@ -255,6 +255,8 @@ struct iommu_group
>   	atomic_t ref;
>   };
>   
> +static struct arm_smmu_device *find_smmu(const struct device *dev);
> +
>   static struct iommu_group *iommu_group_alloc(void)
>   {
>   	struct iommu_group *group = xzalloc(struct iommu_group);
> @@ -443,6 +445,8 @@ static struct iommu_group *iommu_group_get(struct device *dev)
>   #define SMR_VALID			(1U << 31)
>   #define SMR_MASK_SHIFT			16
>   #define SMR_ID_SHIFT			0
> +#define SMR_ID_MASK			0x7fff
> +#define SMR_MASK_MASK			0x7fff
>   
>   #define ARM_SMMU_GR0_S2CR(n)		(0xc00 + ((n) << 2))
>   #define S2CR_CBNDX_SHIFT		0
> @@ -871,6 +875,38 @@ static int register_smmu_master(struct arm_smmu_device *smmu,
>   					     fwspec);
>   }
>   
> +static int arm_smmu_dt_add_device_generic(u8 devfn, struct device *dev)
> +{
> +	struct arm_smmu_device *smmu;
> +	struct iommu_fwspec *fwspec;
> +
> +	fwspec = dev_iommu_fwspec_get(dev);
> +	if (fwspec == NULL)
> +		return -ENXIO;
> +
> +	smmu = find_smmu(fwspec->iommu_dev);
> +	if (smmu == NULL)
> +		return -ENXIO;
> +
> +	return arm_smmu_dt_add_device_legacy(smmu, dev, fwspec);
> +}
> +
> +static int arm_smmu_dt_xlate_generic(struct device *dev,
> +				    const struct dt_phandle_args *spec)
> +{
> +	uint32_t mask, fwid = 0;
> +
> +	if (spec->args_count > 0)
> +		fwid |= (SMR_ID_MASK & spec->args[0]) << SMR_ID_SHIFT;
> +
> +	if (spec->args_count > 1)
> +		fwid |= (SMR_MASK_MASK & spec->args[1]) << SMR_MASK_SHIFT;
> +	else if (!of_property_read_u32(spec->np, "stream-match-mask", &mask))
> +		fwid |= (SMR_MASK_MASK & mask) << SMR_MASK_SHIFT;
> +
> +	return iommu_fwspec_add_ids(dev, &fwid, 1);
> +}
> +
>   static struct arm_smmu_device *find_smmu_for_device(struct device *dev)
>   {
>   	struct arm_smmu_device *smmu;
> @@ -2835,6 +2871,7 @@ static void arm_smmu_iommu_domain_teardown(struct domain *d)
>   static const struct iommu_ops arm_smmu_iommu_ops = {
>       .init = arm_smmu_iommu_domain_init,
>       .hwdom_init = arm_smmu_iommu_hwdom_init,
> +    .add_device = arm_smmu_dt_add_device_generic,
>       .teardown = arm_smmu_iommu_domain_teardown,
>       .iotlb_flush = arm_smmu_iotlb_flush,
>       .iotlb_flush_all = arm_smmu_iotlb_flush_all,
> @@ -2842,9 +2879,10 @@ static const struct iommu_ops arm_smmu_iommu_ops = {
>       .reassign_device = arm_smmu_reassign_dev,
>       .map_page = arm_iommu_map_page,
>       .unmap_page = arm_iommu_unmap_page,
> +    .dt_xlate = arm_smmu_dt_xlate_generic,
>   };
>   
> -static __init const struct arm_smmu_device *find_smmu(const struct device *dev)
> +static struct arm_smmu_device *find_smmu(const struct device *dev)
>   {
>   	struct arm_smmu_device *smmu;
>   	bool found = false;
> diff --git a/xen/drivers/passthrough/device_tree.c b/xen/drivers/passthrough/device_tree.c
> index 911f82a561..af6c2b2dfe 100644
> --- a/xen/drivers/passthrough/device_tree.c
> +++ b/xen/drivers/passthrough/device_tree.c
> @@ -159,22 +159,7 @@ int iommu_add_dt_device(struct dt_device_node *np)
>            * these callback implemented.
>            */
>           if ( !ops->add_device || !ops->dt_xlate )
> -        {
> -            /*
> -             * Some Device Trees may expose both legacy SMMU and generic
> -             * IOMMU bindings together. However, the SMMU driver is only
> -             * supporting the former and will protect them during the
> -             * initialization. So we need to skip them and not return
> -             * error here.
> -             *
> -             * XXX: This can be dropped when the SMMU is able to deal
> -             * with generic bindings.
> -             */
> -            if ( dt_device_is_protected(np) )
> -                return 0;
> -            else
> -                return -EINVAL;
> -        }
> +            return -EINVAL;
>   
>           if ( !dt_device_is_available(iommu_spec.np) )
>               break;
> 

-- 
Julien Grall