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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Date: Fri, 1 Mar 2024 22:33:06 -0800
From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
To: Jian-Hong Pan <jhp@...lessos.org>, Bjorn Helgaas <helgaas@...nel.org>,
 Johan Hovold <johan@...nel.org>, David Box <david.e.box@...ux.intel.com>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: 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)


On 2/15/24 10:26 PM, 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."
>
> Add notes into pci_enable_link_state(_locked) for kernel-doc. Hope these
> notify callers ensuring the devices in D0, if PCI-PM L1 PM Substates are
> going to be enabled.
>
> Signed-off-by: Jian-Hong Pan <jhp@...lessos.org>
> ---

Looks fine to me.

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.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
>   *

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer