linux-kernel - Re: [PATCH] arm64: dts: qcom: x1e80100: enable GICv3 ITS for PCIe

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Message-ID: <20240711164153.GA4992@thinkpad>
Date: Thu, 11 Jul 2024 22:11:53 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Johan Hovold <johan@...nel.org>
Cc: Konrad Dybcio <konrad.dybcio@...aro.org>,
	Johan Hovold <johan+linaro@...nel.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Abel Vesa <abel.vesa@...aro.org>, linux-arm-msm@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: dts: qcom: x1e80100: enable GICv3 ITS for PCIe

On Thu, Jul 11, 2024 at 09:49:52PM +0530, Manivannan Sadhasivam wrote:
> On Thu, Jul 11, 2024 at 05:01:15PM +0200, Johan Hovold wrote:
> > [ +CC: Mani ]
> > 
> > On Thu, Jul 11, 2024 at 11:58:08AM +0200, Johan Hovold wrote:
> > > On Thu, Jul 11, 2024 at 11:54:15AM +0200, Konrad Dybcio wrote:
> > > > On 11.07.2024 11:02 AM, Johan Hovold wrote:
> > > > > The DWC PCIe controller can be used with its internal MSI controller or
> > > > > with an external one such as the GICv3 Interrupt Translation Service
> > > > > (ITS).
> > > > > 
> > > > > Add the msi-map properties needed to use the GIC ITS. This will also
> > > > > make Linux switch to the ITS implementation, which allows for assigning
> > > > > affinity to individual MSIs.
> > 
> > > > X1E CRD throws tons of correctable errors with this on PCIe6a:
> > 
> > > What branch are you using? Abel reported seeing this with his branch
> > > which has a few work-in-progress patches that try to enable 4-lane PCIe.
> > > 
> > > There are no errors with my wip branch based on rc7, and I have the same
> > > drive as Abel.
> > 
> > For some reason I don't get these errors on my machine, but this has now
> > been confirmed by two other people running my rc branch (including Abel)
> > so something is broken here, for example, with the PHY settings.
> > 
> 
> I saw AER errors on Abel's machine during probe with 4-lane PHY settings. And
> that might be the indication why the link width got downgraded to x2. This is
> still not yet resolved.
> 
> > I saw five correctable errors once, when running linux-next, but it took
> > several minutes and they were still minutes apart.
> > 
> > > Also note that the errors happen also without this patch applied, they
> > > are just being reported now.
> > 
> > I guess we need to track down what is causing these errors before
> > enabling ITS (and thereby the error reporting). 
> > 
> > At least L0s is not involved here, as it was with sc8280xp, as the
> > NVMe controllers in question do not support it.
> > 
> > Perhaps something is off because we're running the link at half width?
> > 
> 
> My hunch is the PHY settings. But Abel cross checked the PHY settings with
> internal documentation and they seem to match. Also, Qcom submitted a series
> that is supposed to fix stability issues with Gen4 [1]. With this series, Gen 4
> x4 setup is working on SA8775P-RIDE board as reported by Qcom. But Abel
> confirmed that it didn't help him with the link downgrade issue.
> 
> Perhaps you can give it a try and see if it makes any difference for this issue?
> 
> Meantime, I'm checking with Qcom contacts on this.
> 

One thing I confirmed is, we definitely need different PHY sequence for using
2L. The current PHY settings are for 4L, so limiting the lane count from the
controller is going to be problematic. And AER errors might be due to that as
well.

We need to investigate on enabling 4L.

- Mani

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