linux-kernel - Re: [PATCH v2 2/4] PCI/ASPM: Add pcie_aspm_remove

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Message-ID: <xkrehb72sk7x5iyxbkvydu356hgo5t2xr3asnwiddvhtz5eqam@jlzd6gwg256n>
Date: Wed, 12 Nov 2025 22:57:07 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: linux-pci@...r.kernel.org, Christian Zigotzky <chzigotzky@...osoft.de>, 
	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>, 
	Lukas Wunner <lukas@...ner.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 2/4] PCI/ASPM: Add pcie_aspm_remove_cap() to override
 advertised link states

On Mon, Nov 10, 2025 at 04:22:26PM -0600, Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@...gle.com>
> 
> Add pcie_aspm_remove_cap().  A quirk can use this to prevent use of ASPM
> L0s or L1 link states, even if the device advertised support for them.
> 
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> ---
>  drivers/pci/pci.h       |  2 ++
>  drivers/pci/pcie/aspm.c | 13 +++++++++++++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 4492b809094b..36f8c0985430 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -958,6 +958,7 @@ void pci_save_aspm_l1ss_state(struct pci_dev *dev);
>  void pci_restore_aspm_l1ss_state(struct pci_dev *dev);
>  
>  #ifdef CONFIG_PCIEASPM
> +void pcie_aspm_remove_cap(struct pci_dev *pdev, u32 lnkcap);
>  void pcie_aspm_init_link_state(struct pci_dev *pdev);
>  void pcie_aspm_exit_link_state(struct pci_dev *pdev);
>  void pcie_aspm_pm_state_change(struct pci_dev *pdev, bool locked);
> @@ -965,6 +966,7 @@ void pcie_aspm_powersave_config_link(struct pci_dev *pdev);
>  void pci_configure_ltr(struct pci_dev *pdev);
>  void pci_bridge_reconfigure_ltr(struct pci_dev *pdev);
>  #else
> +static inline void pcie_aspm_remove_cap(struct pci_dev *pdev, u32 lnkcap) { }
>  static inline void pcie_aspm_init_link_state(struct pci_dev *pdev) { }
>  static inline void pcie_aspm_exit_link_state(struct pci_dev *pdev) { }
>  static inline void pcie_aspm_pm_state_change(struct pci_dev *pdev, bool locked) { }
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index 15d50c089070..bc3cb8bc7018 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -1542,6 +1542,19 @@ int pci_enable_link_state_locked(struct pci_dev *pdev, int state)
>  }
>  EXPORT_SYMBOL(pci_enable_link_state_locked);
>  
> +void pcie_aspm_remove_cap(struct pci_dev *pdev, u32 lnkcap)
> +{
> +	if (lnkcap & PCI_EXP_LNKCAP_ASPM_L0S)
> +		pdev->aspm_l0s_support = 0;
> +	if (lnkcap & PCI_EXP_LNKCAP_ASPM_L1)
> +		pdev->aspm_l1_support = 0;
> +
> +	pci_info(pdev, "ASPM:%s%s removed from Link Capabilities to avoid device defect\n",
> +		 lnkcap & PCI_EXP_LNKCAP_ASPM_L0S ? " L0s" : "",
> +		 lnkcap & PCI_EXP_LNKCAP_ASPM_L1 ? " L1" : "");

I think this gives a false impression that the ASPM CAPs are being removed from
the LnkCap register. This function is just removing it from the internal cache
and the LnkCap register is left unchanged.

IMO, either we need to disable relevant CAPs in LnkCap register also or change
the log in this and quirks patches.

- Mani

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