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

On 2021-09-02 13:51, Anders Roxell wrote:

On Wed, 1 Sept 2021 at 11:58, Robin Murphy [off-list ref] wrote:

quoted

On 2021-09-01 09:59, Marek Szyprowski wrote:

quoted

On 21.05.2021 05:03, Wang Xingang wrote:

quoted

From: Xingang Wang <redacted>

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 <redacted>

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

We've seen this on ARM Juno R2 boards too in the Linaro testfarm.

The problem is that the device can't get the "SATA link up" while booting.

see https://lkft.validation.linaro.org/scheduler/job/3416767#L577

Hmm, what's odd there is that you don't seem to be even detecting any of the endpoints there. Notably, the switch (which both the slots and the on-board endpoints are behind) *does* support ACS even though the Root Complex doesn't, so I wonder if it's getting enabled there and causing it to forward TLPs with ACS bits set which the RC doesn't like?

I'm far from a PCI expert, but I might try running this patch on my board to see if anything else stands out.

Robin.

When reverting this patch we are able to see the "SATA link up".

Cheers,
Anders

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