linux-kernel - Re: [PATCH v2 0/4] PCI/ASPM: Allow quirks to avoid L0s and L1

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Message-ID: <20251111154445.GA2175922@bhelgaas>
Date: Tue, 11 Nov 2025 09:44:45 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Lukas Wunner <lukas@...ner.de>
Cc: linux-pci@...r.kernel.org, Christian Zigotzky <chzigotzky@...osoft.de>,
	Manivannan Sadhasivam <mani@...nel.org>,
	mad skateman <madskateman@...il.com>,
	"R . T . Dickinson" <rtd2@...a.co.nz>,
	Darren Stevens <darren@...vens-zone.net>,
	John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
	luigi burdo <intermediadc@...mail.com>, Al <al@...azap.net>,
	Roland <rol7and@....com>, Hongxing Zhu <hongxing.zhu@....com>,
	hypexed@...oo.com.au, linuxppc-dev@...ts.ozlabs.org,
	debian-powerpc@...ts.debian.org, linux-kernel@...r.kernel.org,
	Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH v2 0/4] PCI/ASPM: Allow quirks to avoid L0s and L1

On Tue, Nov 11, 2025 at 10:33:43AM +0100, Lukas Wunner wrote:
> On Mon, Nov 10, 2025 at 04:22:24PM -0600, Bjorn Helgaas wrote:
> > We enabled ASPM too aggressively in v6.18-rc1.  f3ac2ff14834 ("PCI/ASPM:
> > Enable all ClockPM and ASPM states for devicetree platforms") enabled ASPM
> > L0s, L1, and (if advertised) L1 PM Substates.
> > 
> > df5192d9bb0e ("PCI/ASPM: Enable only L0s and L1 for devicetree platforms")
> > (v6.18-rc3) backed off and omitted Clock PM and L1 Substates because we
> > don't have good infrastructure to discover CLKREQ# support, and L1
> > Substates may require device-specific configuration.
> > 
> > L0s and L1 are generically discoverable and should not require
> > device-specific support, but some devices advertise them even though they
> > don't work correctly.  This series is a way to add quirks avoid L0s and L1
> > in this case.
> 
> Reviewed-by: Lukas Wunner <lukas@...ner.de>

Thanks!

> I note that a number of drivers call pci_disable_link_state() or
> pci_disable_link_state_locked() to disable ASPM on probe.
> Can we convert (all of) these to quirks which use the new helper
> introduced here?
> 
> I think that would be useful because it would disable ASPM even if
> the driver isn't available and thus avoid e.g. AER messages caused
> by ASPM issues.
> 
> pcie_aspm_init_link_state() also contains the following code comment:
> 
> 	/*
> 	 * At this stage drivers haven't had an opportunity to change the
> 	 * link policy setting. Enabling ASPM on broken hardware can cripple
> 	 * it even before the driver has had a chance to disable ASPM, so
> 	 * default to a safe level right now. If we're enabling ASPM beyond
> 	 * the BIOS's expectation, we'll do so once pci_enable_device() is
> 	 * called.
> 	 */
> 
> If we'd mask out incorrect or non-working L0s/L1 capabilities for all
> devices early during enumeration via quirks, we wouldn't have to go
> through these contortions of setting up deeper ASPM states only at
> device enable time.

I definitely agree.  I forgot to follow up on all of those cases.
There aren't that many of them, but it looks like probably too many to
address for v6.18, and I *think* it's safe to wait and deal with them
for v6.19.

Bjorn