Re: [PATCH v1] drivers: pci: introduce configurable delay for Rockchip PCIe bus scan

From: Peter Geis <pgwipeout@gmail.com>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: kw@linux.com, heiko@sntech.de, robh@kernel.org,
	linux-pci@vger.kernel.org, shawn.lin@rock-chips.com,
	linux-kernel@vger.kernel.org, lgirdwood@gmail.com,
	linux-rockchip@lists.infradead.org, broonie@kernel.org,
	bhelgaas@google.com,
	linux-kernel-mentees@lists.linuxfoundation.org,
	lpieralisi@kernel.org, linux-arm-kernel@lists.infradead.org,
	Dan Johansen <strit@manjaro.org>
Subject: Re: [PATCH v1] drivers: pci: introduce configurable delay for Rockchip PCIe bus scan
Date: Wed, 10 May 2023 21:07:18 -0400	[thread overview]
Message-ID: <CAMdYzYoa8dhmBx5MUG0yBPwVVXPXHrYNnR0QvKHXvV=JaKuMfw@mail.gmail.com> (raw)
In-Reply-To: <ZFwC/seTfSoaLn0v@bhelgaas>

On Wed, May 10, 2023 at 4:48 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> On Tue, May 09, 2023 at 08:11:29PM -0400, Peter Geis wrote:
> > On Tue, May 9, 2023 at 5:19 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
> > > On Tue, May 09, 2023 at 05:39:12PM +0200, Vincenzo Palazzo wrote:
> > > > Add a configurable delay to the Rockchip PCIe driver to address
> > > > crashes that occur on some old devices, such as the Pine64 RockPro64.
> > > >
> > > > This issue is affecting the ARM community, but there is no
> > > > upstream solution for it yet.
> > >
> > > It sounds like this happens with several endpoints, right?  And I
> > > assume the endpoints work fine in other non-Rockchip systems?  If
> > > that's the case, my guess is the problem is with the Rockchip host
> > > controller and how it's initialized, not with the endpoints.
> > > ...
>
> > The main issue with the rk3399 is the PCIe controller is buggy and
> > triggers a SoC panic when certain error conditions occur that should
> > be handled gracefully. One of those conditions is when an endpoint
> > requests an access to wait and retry later.
>
> I assume this refers to a Completion with Request Retry Status (RRS)?

I'm not sure the full coverage, the test patch from Shawn Lin that
allowed the system to handle the errors has the following description:
"Native defect prevents this RC far from supporting any response from
EP which UR filed is set."

>
> > Many years ago we ran that issue to ground and with Robin Murphy's
> > help we found that while it's possible to gracefully handle that
> > condition it required hijacking the entire arm64 error handling
> > routine. Not exactly scalable for just one SoC.
>
> Do you have a pointer to that discussion?  The URL might save
> repeating the whole exercise and could be useful for the commit log
> when we try to resolve this.

The link to the patch email is here, the full discussion is pretty
easy to follow:
https://lore.kernel.org/linux-pci/2a381384-9d47-a7e2-679c-780950cd862d@rock-chips.com/
Also:
https://lore.kernel.org/linux-rockchip/1f180d4b-9e5d-c829-555b-c9750940361e@web.de/T/#m9c9d4a28a0d3aa064864f188b8ee3b16ce107aff

>
> > The configurable waits allow us to program reasonable times for
> > 90% of the endpoints that come up in the normal amount of time, while
> > being able to adjust it for the other 10% that do not. Some require
> > multiple seconds before they return without error. Part of the reason
> > we don't want to hardcode the wait time is because the probe isn't
> > handled asynchronously, so the kernel appears to hang while waiting
> > for the timeout.
>
> Is there some way for users to figure out that they would need this
> property?  Or is it just "if your kernel panics on boot, try
> adding or increasing "bus-scan-delay-ms" in your DT?

There's a listing of tested cards at:
https://wiki.pine64.org/wiki/ROCKPro64_Hardware_compatibility

Most cards work fine that don't require a large BAR. PCIe switches are
completely dead without the above hack patch. Cards that lie in the
middle are ones that expect BIOS / EFI support to initialize, or ones
that have complex boot roms and don't initialize quickly.
But yes, it's unfortunately going to be "if you panic, increase the
delay" unless a more complete database of cards can be generated.

Very Respectfully,
Peter Geis

>
> Bjorn
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