Re: [PATCH v4] iommu/of: Fix pci_request_acs() before enumerating PCI devices

[Marek Szyprowski]

On 21.05.2021 05:03, Wang Xingang wrote:
> From: Xingang Wang <wangxingang5@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>

This patch landed in linux-next as commit 57a4ab1584e6 ("iommu/of: Fix 
pci_request_acs() before enumerating PCI devices"). Sadly it breaks PCI 
operation on ARM Juno R1 board (arch/arm64/boot/dts/arm/juno-r1.dts). It 
looks that the IOMMU controller is not probed for some reasons:

# cat /sys/kernel/debug/devices_deferred
2b600000.iommu

Reverting this patch on top of current linux-next fixes this issue. If 
you need more information to debug this issue, just let me know.

> ---
>   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 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/of.c b/drivers/pci/of.c
> index da5b414d585a..2313c3f848b0 100644
> --- a/drivers/pci/of.c
> +++ b/drivers/pci/of.c
> @@ -581,9 +581,15 @@ 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;
>   

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland