linux-kernel - Re: [PATCH v3 00/10] arm64: dts: qcom: sc8280xp: PCIe fixes and GICv3 ITS enable

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Date: Wed, 6 Mar 2024 10:12:31 +0100
From: Johan Hovold <johan@...nel.org>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Johan Hovold <johan+linaro@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konrad.dybcio@...aro.org>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>, linux-arm-msm@...r.kernel.org,
	linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 00/10] arm64: dts: qcom: sc8280xp: PCIe fixes and
 GICv3 ITS enable

On Wed, Mar 06, 2024 at 10:48:30AM +0200, Dmitry Baryshkov wrote:
> On Wed, 6 Mar 2024 at 10:39, Manivannan Sadhasivam
> <manivannan.sadhasivam@...aro.org> wrote:
> > On Wed, Mar 06, 2024 at 08:20:16AM +0100, Johan Hovold wrote:
> > > On Wed, Mar 06, 2024 at 12:03:02PM +0530, Manivannan Sadhasivam wrote:

> > > > Just received confirmation from Qcom that L0s is not supported for any of the
> > > > PCIe instances in sc8280xp (and its derivatives). Please move the property to
> > > > SoC dtsi.

> > > Ok, thanks for confirming. But then the devicetree property is not the
> > > right way to handle this, and we should disable L0s based on the
> > > compatible string instead.

> > Hmm. I checked further and got the info that there is no change in the IP, but
> > the PHY sequence is not tuned correctly for L0s (as I suspected earlier). So
> > there will be AERs when L0s is enabled on any controller instance. And there
> > will be no updated PHY sequence in the future also for this chipset.
> 
> Why? If it is a bug in the PHY driver, it should be fixed there
> instead of adding workarounds.

ASPM L0s is currently broken on these platforms and, as far as I
understand, both under Windows and Linux. Since Qualcomm hasn't been
able to come up with the necessary PHY init sequences for these
platforms yet, I doubt they will suddenly appear in the near future.

So we need to disable L0s for now. If an updated PHY init sequence later
appears, we can always enable it again.

> > So yeah, let's disable it in the driver instead.

Johan