linux-kernel - Re: [PATCH v4 2/3] PCI/ASPM: Add notes about enabling PCI-PM L1SS to pci_enable_link_state(

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Message-ID: <20240301212614.GA408494@bhelgaas>
Date: Fri, 1 Mar 2024 15:26:14 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Jian-Hong Pan <jhp@...lessos.org>
Cc: Johan Hovold <johan@...nel.org>,
	David Box <david.e.box@...ux.intel.com>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Damien Le Moal <dlemoal@...nel.org>,
	Nirmal Patel <nirmal.patel@...ux.intel.com>,
	Jonathan Derrick <jonathan.derrick@...ux.dev>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux@...lessos.org
Subject: Re: [PATCH v4 2/3] PCI/ASPM: Add notes about enabling PCI-PM L1SS to
 pci_enable_link_state(_locked)

In subject:

  PCI/ASPM: Document D0 requirement when enabling PCI-PM L1 PM Substates

On Fri, Feb 16, 2024 at 02:26:01PM +0800, Jian-Hong Pan wrote:
> According to PCI Express Base Specification Revision 6.0, Section 5.5.4:
> "If setting either or both of the enable bits for PCI-PM L1 PM Substates,
> both ports must be configured as described in this section while in D0."

"PCIe r6.0, sec 5.5.4" is enough.

> Add notes into pci_enable_link_state(_locked) for kernel-doc.

  Add note about D0 requirement in pci_enable_link_state() kernel-doc.

> Hope these
> notify callers ensuring the devices in D0, if PCI-PM L1 PM Substates are
> going to be enabled.

Skip this part.

> Signed-off-by: Jian-Hong Pan <jhp@...lessos.org>

With above updates,

Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>

> ---
> v3:
> - Fix as readable comments
> 
> v4:
> - The same
> 
>  drivers/pci/pcie/aspm.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index 7f1d674ff171..a39d2ee744cb 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -1416,6 +1416,9 @@ static int __pci_enable_link_state(struct pci_dev *pdev, int state, bool locked)
>   * touch the LNKCTL register. Also note that this does not enable states
>   * disabled by pci_disable_link_state(). Return 0 or a negative errno.
>   *
> + * Note: Ensure devices are in D0 before enabling PCI-PM L1 PM Substates, per
> + * PCIe r6.0, sec 5.5.4.
> + *
>   * @pdev: PCI device
>   * @state: Mask of ASPM link states to enable
>   */
> @@ -1432,6 +1435,9 @@ EXPORT_SYMBOL(pci_enable_link_state);
>   * can't touch the LNKCTL register. Also note that this does not enable states
>   * disabled by pci_disable_link_state(). Return 0 or a negative errno.
>   *
> + * Note: Ensure devices are in D0 before enabling PCI-PM L1 PM Substates, per
> + * PCIe r6.0, sec 5.5.4.
> + *
>   * @pdev: PCI device
>   * @state: Mask of ASPM link states to enable
>   *
> -- 
> 2.43.2
>