Re: [Xen-devel] [PATCH for-4.13] xen/arm: boot with device trees with "mmu-masters" and "iommus"

[Oleksandr <olekstysh@xxxxxxxxx>]

On 30.09.19 23:56, Stefano Stabellini wrote:

Hi Stefano

> Some Device Trees may expose both legacy SMMU and generic IOMMU bindings
> together. However, the SMMU driver in Xen is only supporting the legacy
> SMMU bindings, leading to fatal initialization errors at boot time.
>
> This patch fixes the booting problem by adding a check to
> iommu_add_dt_device: if the Xen driver doesn't support the new generic
> bindings, and the device is behind an IOMMU, do not return error. The
> following iommu_assign_dt_device should succeed.
>
> This check will become superfluous, hence removable, once the Xen SMMU
> driver gets support for the generic IOMMU bindings.
>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
> ---
>   xen/drivers/passthrough/device_tree.c | 17 ++++++++++++++++-
>   1 file changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/xen/drivers/passthrough/device_tree.c 
> b/xen/drivers/passthrough/device_tree.c
> index cc900bac70..27e265b936 100644
> --- a/xen/drivers/passthrough/device_tree.c
> +++ b/xen/drivers/passthrough/device_tree.c
> @@ -155,7 +155,22 @@ int iommu_add_dt_device(struct dt_device_node *np)
>            * these callback implemented.
>            */
>           if ( !ops->add_device || !ops->dt_xlate )
> -            return -EINVAL;
> +        {
> +            /*
> +             * 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;
> +        }
>   
>           if ( !dt_device_is_available(iommu_spec.np) )
>               break;
Patch looks correct and quite well described...


You can add (if needed):

Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>


--
Regards,

Oleksandr Tyshchenko


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