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

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

[Jian-Hong Pan]

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@endlessos.org>
---
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

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

[Bjorn Helgaas]

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@endlessos.org>

With above updates,

Acked-by: Bjorn Helgaas <bhelgaas@google.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
> 

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

[Kuppuswamy Sathyanarayanan]

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@endlessos.org>
> ---

Looks fine to me.

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.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