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

[Robin Murphy]

On 2021-09-02 13:51, Anders Roxell wrote:
> On Wed, 1 Sept 2021 at 11:58, Robin Murphy <robin.murphy@xxxxxxx> wrote:
> > On 2021-09-01 09:59, Marek Szyprowski wrote:
> > > 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
>
> 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