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

[Robin Murphy <robin.murphy@arm.com>]

On 2021-09-02 13:51, Anders Roxell wrote:
> On Wed, 1 Sept 2021 at 11:58, Robin Murphy <robin.murphy@arm.com> wrote:
>>
>> On 2021-09-01 09:59, Marek Szyprowski wrote:
>>> On 21.05.2021 05:03, Wang Xingang 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>
>>>
>>> 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
>