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

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Nov 07, 2024 at 01:29:15PM +0530, Pavankumar Kondeti 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>
> Signed-off-by: Pavankumar Kondeti <quic_pkondeti@quicinc.com>
> ---
> Earlier this patch made it to linux-next but got dropped later as it
> broke PCI on ARM Juno R1 board. AFAICT, this issue is never root caused,
> so resending this patch to get attention again.
> 
> https://lore.kernel.org/all/1621566204-37456-1-git-send-email-wangxingang5@huawei.com/
> 
> The original problem that is being fixed by this patch still exists. In
> my use case, all the PCI VF(s) assigned to a VM are sharing the same
> group since these functions are attached under a Multi function PCIe root port 

FWIW, here are the problem reports (which are buried in the thread
above):

  https://lore.kernel.org/all/01314d70-41e6-70f9-e496-84091948701a@samsung.com/ (Marek)
  https://lore.kernel.org/all/CADYN=9JWU3CMLzMEcD5MSQGnaLyDRSKc5SofBFHUax6YuTRaJA@mail.gmail.com/ (Anders)

Given problem reports, the fact that the patch was acked and reviewed
earlier means nothing.  We have to ensure that any issues are resolved
before considering this patch again.

> emulated by the QEMU. This patch fixes that problem.
> ---
>  drivers/iommu/of_iommu.c | 1 -
>  drivers/pci/of.c         | 8 +++++++-
>  2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> index e7a6a1611d19..f19db52388f5 100644
> --- a/drivers/iommu/of_iommu.c
> +++ b/drivers/iommu/of_iommu.c
> @@ -141,7 +141,6 @@ int of_iommu_configure(struct device *dev, struct device_node *master_np,
>  			.np = master_np,
>  		};
>  
> -		pci_request_acs();
>  		err = pci_for_each_dma_alias(to_pci_dev(dev),
>  					     of_pci_iommu_init, &info);
>  		of_pci_check_device_ats(dev, master_np);
> diff --git a/drivers/pci/of.c b/drivers/pci/of.c
> index dacea3fc5128..dc90f4e45dd3 100644
> --- a/drivers/pci/of.c
> +++ b/drivers/pci/of.c
> @@ -637,9 +637,15 @@ static int pci_parse_request_of_pci_ranges(struct device *dev,
>  
>  int devm_of_pci_bridge_init(struct device *dev, struct pci_host_bridge *bridge)
>  {
> -	if (!dev->of_node)
> +	struct device_node *node = dev->of_node;
> +
> +	if (!node)
>  		return 0;
>  
> +	/* Detect IOMMU and make sure ACS will be enabled */
> +	if (of_property_read_bool(node, "iommu-map"))
> +		pci_request_acs();
> +
>  	bridge->swizzle_irq = pci_common_swizzle;
>  	bridge->map_irq = of_irq_parse_and_map_pci;
>  
> 
> ---
> base-commit: 59b723cd2adbac2a34fc8e12c74ae26ae45bf230
> change-id: 20241107-pci_acs_fix-2239e0fb1768
> 
> Best regards,
> -- 
> Pavankumar Kondeti <quic_pkondeti@quicinc.com>
>