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From:   Bjorn Helgaas <bhelgaas@google.com>
Date:   Thu, 31 Jan 2019 15:49:12 -0600
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Subject: Re: Linux Kernel Regression: HAPS quirk breaks PCIe on i.MX6QP
To:     "Lukas F. Hartmann" <lukas@mntmn.com>
Cc:     thinhn@synopsys.com,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Lucas Stach <l.stach@pengutronix.de>,
        linux-pci@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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[+cc linux-pci, linux-kernel]

On Thu, Jan 31, 2019 at 11:21 AM Lukas F. Hartmann <lukas@mntmn.com> wrote:
>
> Hi Thinh,
>
> I'm writing you because you're the author in this commit:
> https://github.com/torvalds/linux/commit/03e6742584af8866ba014874669d0440bed3a623
>
> This quirk workaround breaks the PCIe on i.MX6QP, at least on my test
> devices. The reason is because the Synposys PCIe IP in i.MX6QP has the
> same device ID as the HAPS USB3 controller you are targeting in the
> commit: 0xabcd.
>
> Definition:
>
> https://github.com/torvalds/linux/blob/master/include/linux/pci_ids.h#L2364
>
> Here is a bit of lspci output on my i.MX6QP machine (without the problem):
>
> mntmn@reform:~/code/linux$ lspci -v
> 00:00.0 PCI bridge: Synopsys, Inc. Device abcd (rev 01) (prog-if 00
>                                           ^^^^
> [Normal decode])
>         Flags: bus master, fast devsel, latency 0, IRQ 307
>         Memory at 01000000 (32-bit, non-prefetchable) [size=1M]
>         Bus: primary=00, secondary=01, subordinate=ff, sec-latency=0
> ...
>
> The failure mode is that the PCIe controller shows up as a USB
> controller and my ath9k wireless PCIe card cannot be assigned the
> proper resources anymore (-ENOMEM even for very small BARs).
>
> Reverting this commit fixes the problem for me. I suggest to make the
> check more specific to the platform/chipset you are targeting.

So Synopsys apparently re-used Device ID 0xabcd?  That's a pretty bad problem.

It looks like we merged 03e6742584af ("PCI: Override Synopsys USB 3.x
HAPS device class") for v5.0, and v5.0-final hasn't been released yet,
so if we don't hear from Thinh with a resolution, we can still revert
it.

I set myself a reminder to revert this on Feb 11, but hopefully we'll
have a better resolution before then.

Bjorn