Re: [PATCH V8 RESEND 1/4] PCI/ASPM: Add pci_enable_link_state()

[Sathyanarayanan Kuppuswamy]

Hi,

On 11/18/22 6:14 PM, David E. Box wrote:
> From: Michael Bottini <michael.a.bottini@xxxxxxxxxxxxxxx>
> 
> Add pci_enable_link_state() to allow devices to change the default BIOS
> configured states. Clears the BIOS default settings then sets the new
> states and reconfigures the link under the semaphore. Also add
> PCIE_LINK_STATE_ALL macro for convenience for callers that want to enable
> all link states.
> 
> Signed-off-by: Michael Bottini <michael.a.bottini@xxxxxxxxxxxxxxx>
> Signed-off-by: David E. Box <david.e.box@xxxxxxxxxxxxxxx>
> Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> ---
>  V8
>   - No change
> 
>  V7
>   - Fix description as suggested by Bjorn
>   - Rename function to pci_enable_link_state
> 
>  V6
>   - No change
>  V5
>   - Rename to pci_enable_default_link_state and model after
>     pci_disable_link_state() as suggested by Bjorn.
>   - Add helper PCIE_LINK_STATE_ALL which sets bits for all links states and
>     clock pm.
>   - Clarify commit language to indicate the function changes the default
>     link states (not ASPM policy).
>  V4
>   - Refactor vmd_enable_apsm() to exit early, making the lines shorter
>     and more readable. Suggested by Christoph.
>  V3
>   - No changes
>  V2
>   - Use return status to print pci_info message if ASPM cannot be enabled.
>   - Add missing static declaration, caught by lkp@xxxxxxxxx
> 
>  drivers/pci/pcie/aspm.c | 54 +++++++++++++++++++++++++++++++++++++++++
>  include/linux/pci.h     |  7 ++++++
>  2 files changed, 61 insertions(+)
> 
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index 53a1fa306e1e..339c686a5094 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -1181,6 +1181,60 @@ int pci_disable_link_state(struct pci_dev *pdev, int state)
>  }
>  EXPORT_SYMBOL(pci_disable_link_state);
>  
> +/**
> + * pci_enable_link_state - Clear and set the default device link state so that
> + * the link may be allowed to enter the specified states. Note that if the
> + * BIOS didn't grant ASPM control to the OS, this does nothing because we 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.
> + *
> + * @pdev: PCI device
> + * @state: Mask of ASPM link states to enable
> + */
> +int pci_enable_link_state(struct pci_dev *pdev, int state)
> +{
> +	struct pcie_link_state *link = pcie_aspm_get_link(pdev);
> +
> +	if (!link)
> +		return -EINVAL;
> +	/*
> +	 * A driver requested that ASPM be enabled on this device, but
> +	 * if we don't have permission to manage ASPM (e.g., on ACPI
> +	 * systems we have to observe the FADT ACPI_FADT_NO_ASPM bit and
> +	 * the _OSC method), we can't honor that request.
> +	 */
> +	if (aspm_disabled) {
> +		pci_warn(pdev, "can't override BIOS ASPM; OS doesn't have ASPM control\n");
> +		return -EPERM;
> +	}
> +
> +	down_read(&pci_bus_sem);
> +	mutex_lock(&aspm_lock);
> +	link->aspm_default = 0;
> +	if (state & PCIE_LINK_STATE_L0S)
> +		link->aspm_default |= ASPM_STATE_L0S;
> +	if (state & PCIE_LINK_STATE_L1)
> +		/* L1 PM substates require L1 */
> +		link->aspm_default |= ASPM_STATE_L1 | ASPM_STATE_L1SS;
> +	if (state & PCIE_LINK_STATE_L1_1)
> +		link->aspm_default |= ASPM_STATE_L1_1;
> +	if (state & PCIE_LINK_STATE_L1_2)
> +		link->aspm_default |= ASPM_STATE_L1_2;
> +	if (state & PCIE_LINK_STATE_L1_1_PCIPM)
> +		link->aspm_default |= ASPM_STATE_L1_1_PCIPM;
> +	if (state & PCIE_LINK_STATE_L1_2_PCIPM)
> +		link->aspm_default |= ASPM_STATE_L1_2_PCIPM;
> +	pcie_config_aspm_link(link, policy_to_aspm_state(link));
> +
> +	link->clkpm_default = (state & PCIE_LINK_STATE_CLKPM) ? 1 : 0;
> +	pcie_set_clkpm(link, policy_to_clkpm_state(link));
> +	mutex_unlock(&aspm_lock);
> +	up_read(&pci_bus_sem);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(pci_enable_link_state);

I see that this function and __pci_disable_link_state() are very similar. Can
this be merged? something like __pci_config_link_state(enable or disable)?

> +
>  static int pcie_aspm_set_policy(const char *val,
>  				const struct kernel_param *kp)
>  {
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 2bda4a4e47e8..8c35f15e6012 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1651,10 +1651,15 @@ extern bool pcie_ports_native;
>  #define PCIE_LINK_STATE_L1_2		BIT(4)
>  #define PCIE_LINK_STATE_L1_1_PCIPM	BIT(5)
>  #define PCIE_LINK_STATE_L1_2_PCIPM	BIT(6)
> +#define PCIE_LINK_STATE_ALL		(PCIE_LINK_STATE_L0S | PCIE_LINK_STATE_L1 |\
> +					 PCIE_LINK_STATE_CLKPM | PCIE_LINK_STATE_L1_1 |\
> +					 PCIE_LINK_STATE_L1_2 | PCIE_LINK_STATE_L1_1_PCIPM |\
> +					 PCIE_LINK_STATE_L1_2_PCIPM)
>  
>  #ifdef CONFIG_PCIEASPM
>  int pci_disable_link_state(struct pci_dev *pdev, int state);
>  int pci_disable_link_state_locked(struct pci_dev *pdev, int state);
> +int pci_enable_link_state(struct pci_dev *pdev, int state);
>  void pcie_no_aspm(void);
>  bool pcie_aspm_support_enabled(void);
>  bool pcie_aspm_enabled(struct pci_dev *pdev);
> @@ -1663,6 +1668,8 @@ static inline int pci_disable_link_state(struct pci_dev *pdev, int state)
>  { return 0; }
>  static inline int pci_disable_link_state_locked(struct pci_dev *pdev, int state)
>  { return 0; }
> +static inline int pci_enable_link_state(struct pci_dev *pdev, int state)
> +{ return 0; }
>  static inline void pcie_no_aspm(void) { }
>  static inline bool pcie_aspm_support_enabled(void) { return false; }
>  static inline bool pcie_aspm_enabled(struct pci_dev *pdev) { return false; }

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer