linux-kernel - Re: [PATCH] PCI: Disallow ASPM on ASMedia ASM1083/1085 PCIe-PCI bridge

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Date:   Wed, 22 Jul 2020 19:41:50 -0600
From:   Robert Hancock <hancockrwd@...il.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     linux-pci@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>, stable@...r.kernel.org,
        Puranjay Mohan <puranjay12@...il.com>
Subject: Re: [PATCH] PCI: Disallow ASPM on ASMedia ASM1083/1085 PCIe-PCI bridge

On Wed, Jul 22, 2020 at 7:04 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Wed, Jul 22, 2020 at 06:46:06PM -0600, Robert Hancock wrote:
> > On Wed, Jul 22, 2020 at 11:40 AM Bjorn Helgaas <helgaas@...nel.org> wrote:
> > > On Tue, Jul 21, 2020 at 08:18:03PM -0600, Robert Hancock wrote:
> > > > Recently ASPM handling was changed to no longer disable ASPM on all
> > > > PCIe to PCI bridges. Unfortunately these ASMedia PCIe to PCI bridge
> > > > devices don't seem to function properly with ASPM enabled, as they
> > > > cause the parent PCIe root port to cause repeated AER timeout errors.
> > > > In addition to flooding the kernel log, this also causes the machine
> > > > to wake up immediately after suspend is initiated.
> > >
> > > Hi Robert, thanks a lot for the report of this problem
> > > (https://lore.kernel.org/r/CADLC3L1R2hssRjxHJv9yhdN_7-hGw58rXSfNp-FraZh0Tw+gRw@mail.gmail.com
> > > and https://bugzilla.redhat.com/show_bug.cgi?id=1853960).
> > >
> > > I'm pretty sure Linux ASPM support is missing some things.  This
> > > problem might be a hardware problem where a quirk is the right
> > > solution, but it could also be that it's a result of a Linux defect
> > > that we should fix.
> > >
> > > Could you collect the dmesg log and "sudo lspci -vvxxxx" output
> > > somewhere (maybe a bugzilla.kernel.org issue)?  I want to figure out
> > > whether this L1 PM substates are enabled on this link, and whether
> > > that's configured correctly.
> >
> > Created a Bugzilla entry and added dmesg and lspci output:
> > https://bugzilla.kernel.org/show_bug.cgi?id=208667
> >
> > As I noted in that report, I subsequently found this page on ASMedia's
> > site: https://www.asmedia.com.tw/eng/e_show_products.php?cate_index=169&item=114
> > which indicates this ASM1083 device has "No PCIe ASPM support".
>
> How nice.  According to your lspci, the device itself claims to
> support ASPM:
>
>   02:00.0 ... ASMedia Technology Inc. ASM1083/1085 PCIe to PCI Bridge
>     LnkCap: ... ASPM L0s L1 ...
>
> but the web page claims otherwise.  That would mean the device is
> defective for claiming something that's not true.  Or possibly those
> capability bits can be set by BIOS.
>
> > It's not clear why this problem isn't occurring on Windows however -
> > either it is not enabling ASPM, somehow it doesn't cause issues with
> > the PCIe link, or it is causing issues and just doesn't notify the
> > user in any way. I can try and check if this bridge device is ending
> > up with ASPM enabled under Windows 10 or not..
>
> If Windows *does* manage to enable ASPM, that would be interesting.  I
> don't know whether Windows has a similar quirk mechanism.  I suppose
> they must have *some* way to work around defective devices.

As I posted on the Bugzilla report, based on lspci output it appears
Windows does have ASPM L0s enabled for this bridge. However, it
appears to have the exact same problem: there are correctable PCIe
error entries showing up in the Windows system event log against the
root port the bridge is connected to. So I am thinking this hardware
is just broken with ASPM enabled.