Re: [PATCH v3] iommu/of: Fix pci_request_acs() before enumerating PCI devices

[Rob Herring <robh@kernel.org>]

On Thu, May 20, 2021 at 2:28 AM Wang Xingang <wangxingang5@huawei.com> wrote:
>
> From: Xingang Wang <wangxingang5@huawei.com>
>
> When booting with devicetree, the pci_request_acs() is called after the
> enumeration and initialization of PCI devices, thus the ACS is not
> enabled. And ACS should be enabled when IOMMU is detected for the
> PCI host bridge, so add check for IOMMU before probe of PCI host and call
> pci_request_acs() to make sure ACS will be enabled when enumerating PCI
> devices.
>
> Fixes: 6bf6c24720d33 ("iommu/of: Request ACS from the PCI core when
> configuring IOMMU linkage")
> Signed-off-by: Xingang Wang <wangxingang5@huawei.com>
> ---
>  drivers/iommu/of_iommu.c                 |  1 -
>  drivers/pci/controller/pci-host-common.c | 17 +++++++++++++++++
>  2 files changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> index a9d2df001149..54a14da242cc 100644
> --- a/drivers/iommu/of_iommu.c
> +++ b/drivers/iommu/of_iommu.c
> @@ -205,7 +205,6 @@ const struct iommu_ops *of_iommu_configure(struct device *dev,
>                         .np = master_np,
>                 };
>
> -               pci_request_acs();
>                 err = pci_for_each_dma_alias(to_pci_dev(dev),
>                                              of_pci_iommu_init, &info);
>         } else {
> diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
> index d3924a44db02..5904ad0bd9ae 100644
> --- a/drivers/pci/controller/pci-host-common.c
> +++ b/drivers/pci/controller/pci-host-common.c

This file is generally only for ECAM compliant hosts. Are those the
only hosts we need to support this? From the looks of dts files with
iommu-map, that would be dropping support in lots of cases.

Perhaps in devm_of_pci_bridge_init() or one of the functions it calls
is the better place.

> @@ -49,6 +49,21 @@ static struct pci_config_window *gen_pci_init(struct device *dev,
>         return cfg;
>  }
>
> +static void pci_host_enable_acs(struct pci_host_bridge *bridge)
> +{
> +       struct device_node *np = bridge->dev.parent->of_node;
> +       static bool acs_enabled;
> +
> +       if (!np || acs_enabled)
> +               return;
> +
> +       /* Detect IOMMU and make sure ACS will be enabled */
> +       if (of_property_read_bool(np, "iommu-map")) {
> +               acs_enabled = true;
> +               pci_request_acs();

Given this function just sets a variable, I don't think you need the
static acs_enabled here.

> +       }
> +}
> +
>  int pci_host_common_probe(struct platform_device *pdev)
>  {
>         struct device *dev = &pdev->dev;
> @@ -81,6 +96,8 @@ int pci_host_common_probe(struct platform_device *pdev)
>         bridge->ops = (struct pci_ops *)&ops->pci_ops;
>         bridge->msi_domain = true;
>
> +       pci_host_enable_acs(bridge);
> +
>         return pci_host_probe(bridge);
>  }
>  EXPORT_SYMBOL_GPL(pci_host_common_probe);
> --
> 2.19.1
>