linux-kernel - Re: [PATCH] PCI/ASPM: Enable only L0s and L1 for devicetree platforms

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Message-ID: <aP9C0H_2XVk6MiLV@hovoldconsulting.com>
Date: Mon, 27 Oct 2025 11:00:48 +0100
From: Johan Hovold <johan@...nel.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: linux-pci@...r.kernel.org,
	Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>,
	Christian Zigotzky <chzigotzky@...osoft.de>,
	FUKAUMI Naoki <naoki@...xa.com>,
	Herve Codina <herve.codina@...tlin.com>,
	Diederik de Haas <diederik@...ow-tech.com>,
	Dragan Simic <dsimic@...jaro.org>, linuxppc-dev@...ts.ozlabs.org,
	linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Shawn Lin <shawn.lin@...k-chips.com>, Frank Li <Frank.li@....com>
Subject: Re: [PATCH] PCI/ASPM: Enable only L0s and L1 for devicetree platforms

On Fri, Oct 24, 2025 at 03:39:24PM -0500, Bjorn Helgaas wrote:
> On Fri, Oct 24, 2025 at 05:20:33PM +0200, Johan Hovold wrote:
> > On Fri, Oct 24, 2025 at 05:12:38PM +0200, Johan Hovold wrote:

> > > Note that this will regress ASPM on Qualcomm platforms further by
> > > disabling L1SS for devices that do not use pwrctrl (e.g. NVMe). ASPM
> > > with pwrctrl is already broken since 6.15. [1]
> > 
> > Actually, the 6.15 regression was fixed in 6.18-rc1 by the offending
> > commit, but pwrctrl devices will now also regress again.
> > 
> > > Reverting also a729c1664619 ("PCI: qcom: Remove custom ASPM enablement
> > > code") should avoid the new regression until a proper fix for the 6.15
> > > regression is in place.
> 
> Help me think through this.  I just sent a pull request [2] that
> includes df5192d9bb0e ("PCI/ASPM: Enable only L0s and L1 for
> devicetree platforms").  If all goes well, v6.18-rc3 will enable L0s
> and L1 (but not L1SS) on Qualcomm platforms.
> 
> IIUC, if we then revert a729c1664619 ("PCI: qcom: Remove custom ASPM
> enablement code"), it will enable L1SS again, but since this is done
> in a dw_pcie_host_ops .post_init() hook, L1SS will only be enabled for
> devices powered on at qcom-pcie probe time.  It will *not* be enabled
> for pwrctrl devices because .post_init() was run when those devices
> were powered off.

Correct.

> I think this is the same as in v6.17.  v6.18-rc1 enabled L1SS for
> everything, including pwrctrl devices, because it was done in the PCI
> enumeration path, not the host controller probe path.  I think that
> enumeration is the right place to do this, but we need to figure out
> how to do it in a generic way.  At a minimum, we need to know that
> CLKREQ# is supported, and some platforms like dw-rockchip also need
> device-specific configuration [3].
> 
> Bottom line, I think we need to revert a729c1664619 for v6.18 to get
> all ASPM states including L1SS enabled on Qualcomm platforms for
> non-pwrctrl devices.  I'll post a patch for this.

Right, that would at least restore the 6.17 state of things with respect
to Qualcomm machines.
 
> Then try to figure out how to make this work for pwrctrl devices for
> v6.19.  Does this sound right?

Yes, unless you can come up with a simple way to enable L1SS during
enumeration on Qualcomm platforms, for example, using a driver callback
that returns true for platforms using the 1.9.0 ops to indicate that
L1SS is supported. That should address also the 6.15 pwrctrl regression.

Johan