Re: [PATCH] PCI/ASPM: Enable L0s/L1 for removable devices when BIOS didn't configure ASPM

[Rafael J. Wysocki]

+Mika Westerberg

On Tue, May 5, 2026 at 12:53 AM Mario Limonciello
<mario.limonciello@xxxxxxx> wrote:
>
> When comparing lspci output between Windows and Linux for hotplugged
> Thunderbolt 5 eGPU devices, Windows enables ASPM L1 but Linux doesn't:
>
>   Windows: LnkCtl: ASPM L1 Enabled
>   Linux:   LnkCtl: ASPM Disabled
>
> This difference in ASPM configuration can cause behavioral differences
> between the two operating systems for the same hardware.
>
> The root cause is that Linux's default ASPM policy (POLICY_DEFAULT) relies
> on firmware/BIOS configuration. For hotplugged devices like Thunderbolt/USB4
> eGPUs, the BIOS may not have configured ASPM since the device wasn't present
> at boot time. As a result, link->aspm_enabled is 0, link->aspm_default is
> set to 0, and Linux never enables ASPM for these devices.
>
> Devicetree platforms already have special handling to enable L0s/L1 by
> default regardless of firmware configuration. Extend this same logic to
> removable devices when firmware hasn't configured any ASPM states.
>
> This makes Linux behavior more consistent with Windows for hotplugged
> Thunderbolt/USB4 devices.
>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=221319
> Assisted-by: Claude Opus 4.6 <noreply@xxxxxxxxxxxxx>
> Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
> ---
>  drivers/pci/pcie/aspm.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index 925373b98dff0..77497d90be0b7 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -804,8 +804,15 @@ static void pcie_aspm_override_default_link_state(struct pcie_link_state *link)
>         struct pci_dev *pdev = link->downstream;
>         u32 override;
>
> -       /* For devicetree platforms, enable L0s and L1 by default */
> -       if (of_have_populated_dt()) {
> +       /*
> +        * For devicetree platforms, enable L0s and L1 by default.
> +        *
> +        * For removable devices (e.g., Thunderbolt/USB4), enable L0s and L1
> +        * by default if BIOS didn't configure any ASPM states. This handles
> +        * hotplugged devices where firmware may not have configured ASPM.
> +        */
> +       if (of_have_populated_dt() ||
> +           (dev_is_removable(&pdev->dev) && !link->aspm_enabled)) {
>                 if (link->aspm_support & PCIE_LINK_STATE_L0S)
>                         link->aspm_default |= PCIE_LINK_STATE_L0S;
>                 if (link->aspm_support & PCIE_LINK_STATE_L1)
> --
> 2.43.0
>