linux-kernel - Re: [PATCH] PCI: qcom: Clear ASPM L0s CAP for MSM8996 SoC

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Message-ID: <7rmiof6lxrr27vd4rnilc6ynxj7c2eiv33uw62lt4sheylpjny@6m2nuqnbnifc>
Date: Thu, 27 Nov 2025 19:25:52 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>, 
	lpieralisi@...nel.org, kwilczynski@...nel.org, bhelgaas@...gle.com, robh@...nel.org, 
	linux-pci@...r.kernel.org, linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Subject: Re: [PATCH] PCI: qcom: Clear ASPM L0s CAP for MSM8996 SoC

On Thu, Nov 27, 2025 at 11:55:15AM +0100, Konrad Dybcio wrote:
> On 11/26/25 9:17 AM, Manivannan Sadhasivam wrote:
> > From: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
> > 
> > Though I couldn't confirm the ASPM L0s support with the Qcom hardware team,
> > bug report from Dmitry suggests that L0s is broken on this legacy SoC.
> > Hence, clear the L0s CAP for the Root Ports in this SoC.
> 
> FWIW if we trust the downstream DT, we have this hunk:
> 
> arch/arm64/boot/dts/qcom/msm8996.dtsi
> 1431:           qcom,l1-supported;
> 1432:           qcom,l1ss-supported;
> 1586:           qcom,l1-supported;
> 1587:           qcom,l1ss-supported;
> 1739:           qcom,l1-supported;
> 1740:           qcom,l1ss-supported;
> 
> But also funnily enough, msm8996auto boards specifically manually
> do a /delete-property/ on those..
> 
> (there exists one 'qcom,l0s-supported', but it's NOT set for 8996, 98,
> or 845)
> 
> On msm-4.14, this became "qcom,no-l0s/l1/l1ss-supported". This forbids L0s
> on at least 8150 and 8250.
> 
> Later, both hosts on SM8350 and SM8450-PCIe0 (not 1) forbid L0s.
> 

Thanks for digging in. Unfortunately, I have to rely on word of mouth to get the
ASPM capability as there is no proper doc that says which SoC supports which
state. And, I'm quite nervous to trust downstream DTS as they were not very
accurate in describing the hardware capabilities. But I think we should atleast
consider the 'no-l0s' properties seriously.

Let me go through all DTS and build try to build a sane ASPM compatibility
table. But just be clear, the above exercise should not block this patch as it
fixes a real issue that has been reported.

> SM8350-PCIe0 sets 'qcom,l1ss-sleep-disable' which influences some RPMh
> things, but also prevents some clock ops wrt the CLKREF source
> 

We can ignore 'qcom,l1ss-sleep-disable' as it is a Qcom low power feature built
around PCIe L1ss, which is not yet supported in upstream.

- Mani

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