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Date:   Tue, 25 Oct 2022 16:14:18 -0700 (PDT)
From:   Stefano Stabellini <sstabellini@kernel.org>
To:     Oleksandr Tyshchenko <olekstysh@gmail.com>
cc:     xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        Juergen Gross <jgross@suse.com>,
        Xenia Ragiadakou <burzalodowa@gmail.com>
Subject: Re: [PATCH V4 2/2] xen/virtio: Handle PCI devices which Host controller
 is described in DT
In-Reply-To: <20221025162004.8501-3-olekstysh@gmail.com>
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References: <20221025162004.8501-1-olekstysh@gmail.com> <20221025162004.8501-3-olekstysh@gmail.com>
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On Tue, 25 Oct 2022, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> 
> Use the same "xen-grant-dma" device concept for the PCI devices
> behind device-tree based PCI Host controller, but with one modification.
> Unlike for platform devices, we cannot use generic IOMMU bindings
> (iommus property), as we need to support more flexible configuration.
> The problem is that PCI devices under the single PCI Host controller
> may have the backends running in different Xen domains and thus have
> different endpoints ID (backend domains ID).
> 
> Add ability to deal with generic PCI-IOMMU bindings (iommu-map/
> iommu-map-mask properties) which allows us to describe relationship
> between PCI devices and backend domains ID properly.
> 
> To avoid having to look up for the PCI Host bridge twice and reduce
> the amount of checks pass an extra struct device_node *np to
> xen_dt_grant_init_backend_domid().
> 
> So with current patch the code expects iommus property for the platform
> devices and iommu-map/iommu-map-mask properties for PCI devices.
> 
> The example of generated by the toolstack iommu-map property
> for two PCI devices 0000:00:01.0 and 0000:00:02.0 whose
> backends are running in different Xen domains with IDs 1 and 2
> respectively:
> iommu-map = <0x08 0xfde9 0x01 0x08 0x10 0xfde9 0x02 0x08>;
> 
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>

Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>


> ---
> Slightly RFC. This is needed to support Xen grant mappings for virtio-pci devices
> on Arm at some point in the future. The Xen toolstack side is not completely ready yet.
> Here, for PCI devices we use more flexible way to pass backend domid to the guest
> than for platform devices.
> 
> Changes V1 -> V2:
>    - update commit description
>    - rebase
>    - rework to use generic PCI-IOMMU bindings instead of generic IOMMU bindings
> 
> Changes V2 -> V3:
>    - update commit description, add an example
>    - drop xen_dt_map_id() and squash xen_dt_get_pci_host_node() with
>      xen_dt_get_node()
>    - pass struct device_node *np to xen_is_dt_grant_dma_device() and
>      xen_dt_grant_init_backend_domid()
>    - pass domid_t *backend_domid instead of struct xen_grant_dma_data *data
>      to xen_dt_grant_init_backend_domid()
> 
> Changes V3 -> V4:
>    - just rebase on new prereq patch
>      "xen/virtio: Optimize the setup of "xen-grant-dma" devices"
> 
> Previous discussion is at:
> https://lore.kernel.org/xen-devel/20221006174804.2003029-1-olekstysh@gmail.com/
> https://lore.kernel.org/xen-devel/20221015153409.918775-1-olekstysh@gmail.com/
> https://lore.kernel.org/xen-devel/20221021172408.77397-1-olekstysh@gmail.com/
> 
> Based on:
> https://git.kernel.org/pub/scm/linux/kernel/git/xen/tip.git/log/?h=for-linus-6.1
> ---
> ---
>  drivers/xen/grant-dma-ops.c | 46 +++++++++++++++++++++++++++++++------
>  1 file changed, 39 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c
> index 1e797a043980..9784a77fa3c9 100644
> --- a/drivers/xen/grant-dma-ops.c
> +++ b/drivers/xen/grant-dma-ops.c
> @@ -10,6 +10,7 @@
>  #include <linux/module.h>
>  #include <linux/dma-map-ops.h>
>  #include <linux/of.h>
> +#include <linux/pci.h>
>  #include <linux/pfn.h>
>  #include <linux/xarray.h>
>  #include <linux/virtio_anchor.h>
> @@ -292,15 +293,43 @@ static const struct dma_map_ops xen_grant_dma_ops = {
>  	.dma_supported = xen_grant_dma_supported,
>  };
>  
> +static struct device_node *xen_dt_get_node(struct device *dev)
> +{
> +	if (dev_is_pci(dev)) {
> +		struct pci_dev *pdev = to_pci_dev(dev);
> +		struct pci_bus *bus = pdev->bus;
> +
> +		/* Walk up to the root bus to look for PCI Host controller */
> +		while (!pci_is_root_bus(bus))
> +			bus = bus->parent;
> +
> +		return of_node_get(bus->bridge->parent->of_node);
> +	}
> +
> +	return of_node_get(dev->of_node);
> +}
> +
>  static int xen_dt_grant_init_backend_domid(struct device *dev,
> +					   struct device_node *np,
>  					   domid_t *backend_domid)
>  {
> -	struct of_phandle_args iommu_spec;
> +	struct of_phandle_args iommu_spec = { .args_count = 1 };
>  
> -	if (of_parse_phandle_with_args(dev->of_node, "iommus", "#iommu-cells",
> -			0, &iommu_spec)) {
> -		dev_dbg(dev, "Cannot parse iommus property\n");
> -		return -ESRCH;
> +	if (dev_is_pci(dev)) {
> +		struct pci_dev *pdev = to_pci_dev(dev);
> +		u32 rid = PCI_DEVID(pdev->bus->number, pdev->devfn);
> +
> +		if (of_map_id(np, rid, "iommu-map", "iommu-map-mask", &iommu_spec.np,
> +				iommu_spec.args)) {
> +			dev_dbg(dev, "Cannot translate ID\n");
> +			return -ESRCH;
> +		}
> +	} else {
> +		if (of_parse_phandle_with_args(np, "iommus", "#iommu-cells",
> +				0, &iommu_spec)) {
> +			dev_dbg(dev, "Cannot parse iommus property\n");
> +			return -ESRCH;
> +		}
>  	}
>  
>  	if (!of_device_is_compatible(iommu_spec.np, "xen,grant-dma") ||
> @@ -324,10 +353,13 @@ static int xen_dt_grant_init_backend_domid(struct device *dev,
>  static int xen_grant_init_backend_domid(struct device *dev,
>  					domid_t *backend_domid)
>  {
> +	struct device_node *np;
>  	int ret = -ENODEV;
>  
> -	if (dev->of_node) {
> -		ret = xen_dt_grant_init_backend_domid(dev, backend_domid);
> +	np = xen_dt_get_node(dev);
> +	if (np) {
> +		ret = xen_dt_grant_init_backend_domid(dev, np, backend_domid);
> +		of_node_put(np);
>  	} else if (IS_ENABLED(CONFIG_XEN_VIRTIO_FORCE_GRANT) || xen_pv_domain()) {
>  		dev_info(dev, "Using dom0 as backend\n");
>  		*backend_domid = 0;
> -- 
> 2.25.1
>