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    SubjectRe: [PATCH V4 2/2] xen/virtio: Handle PCI devices which Host controller is described in DT
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    On 10/25/22 19:20, 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: Xenia Ragiadakou <burzalodowa@gmail.com>

    > ---
    > 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;

    --
    Xenia

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