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 15:08:57 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Johan Hovold <johan@...nel.org>
Cc: Dmitry Baryshkov <dmitry.baryshkov@...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 10:12:31AM +0100, Johan Hovold wrote:
> 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.
> 

It could be the same case for all 'non-mobile' chipsets (automotive, compute,
modem). So instead of using the compatible, please add a flag and set that for
all non-mobile SoCs. Like the ones starting with SAxxx, SCxxx, SDxxx.

- Mani

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