On Mon, Jul 14, 2025 at 11:31:04PM +0530, Manivannan Sadhasivam wrote:
> Commit 9f4f3dfad8cf ("PCI: qcom: Enable ASPM for platforms supporting 1.9.0
> ops") allowed the Qcom controller driver to enable ASPM for all PCI devices
> enumerated at the time of the controller driver probe. It proved to be
> useful for devices already powered on by the bootloader as it allowed
> devices to enter ASPM without user intervention.
>
> However, it could not enable ASPM for the hotplug capable devices i.e.,
> devices enumerated *after* the controller driver probe. This limitation
> mostly went unnoticed as the Qcom PCI controllers are not hotplug capable
> and also the bootloader has been enabling the PCI devices before Linux
> Kernel boots (mostly on the Qcom compute platforms which users use on a
> daily basis).
>
> But with the advent of the commit b458ff7e8176 ("PCI/pwrctl: Ensure that
> pwrctl drivers are probed before PCI client drivers"), the pwrctrl driver
> started to block the PCI device enumeration until it had been probed.
> Though, the intention of the commit was to avoid race between the pwrctrl
> driver and PCI client driver, it also meant that the pwrctrl controlled PCI
> devices may get probed after the controller driver and will no longer have
> ASPM enabled. So users started noticing high runtime power consumption with
> WLAN chipsets on Qcom compute platforms like Thinkpad X13s, and Thinkpad
> T14s, etc...
>
> Obviously, it is the pwrctrl change that caused regression, but it
> ultimately uncovered a flaw in the ASPM enablement logic of the controller
> driver. So to address the actual issue, switch to the bus notifier for
> enabling ASPM of the PCI devices. The notifier will notify the controller
> driver when a PCI device is attached to the bus, thereby allowing it to
> enable ASPM more reliably. It should be noted that the
> 'pci_dev::link_state', which is required for enabling ASPM by the
> pci_enable_link_state_locked() API, is only set by the time of
> BUS_NOTIFY_BIND_DRIVER stage of the notification. So we cannot enable ASPM
> during BUS_NOTIFY_ADD_DEVICE stage.
A problem with this approach is that ASPM will never be enabled (and
power consumption will be higher) in case an endpoint driver is missing.
I think that's something we should try to avoid.
> So with this, we can also get rid of the controller driver specific
> 'qcom_pcie_ops::host_post_init' callback.
>
> Cc: stable@xxxxxxxxxxxxxxx # v6.7
> Fixes: 9f4f3dfad8cf ("PCI: qcom: Enable ASPM for platforms supporting 1.9.0 ops")
> Reported-by: Johan Hovold <johan@xxxxxxxxxx>
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxxxxxxxx>
Note that the patch fails to apply to 6.16-rc6 due to changes in
linux-next. Depending on how fast we can come up with a fix it may be
better to target 6.16.
> -static int qcom_pcie_enable_aspm(struct pci_dev *pdev, void *userdata)
> -{
> - /*
> - * Downstream devices need to be in D0 state before enabling PCI PM
> - * substates.
> - */
> - pci_set_power_state_locked(pdev, PCI_D0);
> - pci_enable_link_state_locked(pdev, PCIE_LINK_STATE_ALL);
> -
> - return 0;
> -}
I think you should consider leaving this helper in place here to keep
the size of the diff down (e.g. as you intend to backport this).
> +static int qcom_pcie_enable_aspm(struct pci_dev *pdev)
> +{
> + /*
> + * Downstream devices need to be in D0 state before enabling PCI PM
> + * substates.
> + */
> + pci_set_power_state_locked(pdev, PCI_D0);
> + pci_enable_link_state_locked(pdev, PCIE_LINK_STATE_ALL);
You need to use the non-locked helpers here since you no longer hold the
bus semaphore (e.g. as reported by lockdep).
Maybe this makes the previous comment about not moving the helper moot.
> +
> + return 0;
> +}
> +
> +static int pcie_qcom_notify(struct notifier_block *nb, unsigned long action,
> + void *data)
> +{
> + struct qcom_pcie *pcie = container_of(nb, struct qcom_pcie, nb);
This results in an unused variable warning (presumably until the next
patch in the series is applied).
> + struct device *dev = data;
> + struct pci_dev *pdev = to_pci_dev(dev);
> +
> + switch (action) {
> + case BUS_NOTIFY_BIND_DRIVER:
> + qcom_pcie_enable_aspm(pdev);
> + break;
> + }
> +
> + return NOTIFY_DONE;
> +}
Missing newline.
> static int qcom_pcie_probe(struct platform_device *pdev)
> {
> const struct qcom_pcie_cfg *pcie_cfg;
Johan
