Re: [PATCH V3 1/2] PCI/ASPM: Add host-bridge API to override default ASPM/CLKPM link state

[Kenneth Crudup <kenny@panix.com>]

Any movement on this?

Anything keeping it from being in pm-next (at least I haven't seen it in 
a precursory look for it)?

Thanks,

-Kenny

On 9/4/25 14:11, Kenneth Crudup wrote:
> 
> Tested-by: Kenneth R. Crudup <kenny@panix.com>
> 
> On 8/25/25 13:35, David E. Box wrote:
>> Synthetic PCIe hierarchies, such as those created by Intel VMD, are not
>> enumerated by firmware and do not receive BIOS-provided ASPM or CLKPM
>> defaults. Devices in such domains may therefore run without the intended
>> power management.
>>
>> Add a host-bridge mechanism that lets controller drivers supply their own
>> defaults. A new aspm_default_link_state field in struct 
>> pci_host_bridge is
>> set via pci_host_set_default_pcie_link_state(). During link 
>> initialization,
>> if this field is non-zero, ASPM and CLKPM defaults come from it 
>> instead of
>> BIOS.
>>
>> This enables drivers like VMD to align link power management with 
>> platform
>> expectations and avoids embedding controller-specific quirks in ASPM core
>> logic.
>>
>> Link: https://patchwork.ozlabs.org/project/linux-pci/ 
>> patch/20250720190140.2639200-1-david.e.box%40linux.intel.com/
>> Signed-off-by: David E. Box <david.e.box@linux.intel.com>
>> Tested-by: Manivannan Sadhasivam <mani@kernel.org>
>> Reviewed-by: Rafael J. Wysocki (Intel) <rafael@kernel.org>
>> ---
>> Changes in V3:
>>    -- Changed pci_host_get_default_pcie_link_state() argument name from
>>       parent to dev.
>>    -- Applied changelog tags
>>
>> Changes in V2:
>>
>>    -- Host field name changed to aspm_default_link_state.
>>    -- Added get/set functions for aspm_default_link_state. Only the
>>       setter is exported. Added a kernel-doc describing usage and
>>       particulars around meaning of 0.
>>
>> Changes in V1 from RFC:
>>
>>    -- Rename field to aspm_dflt_link_state since it stores
>>       PCIE_LINK_STATE_XXX flags, not a policy enum.
>>    -- Move the field to struct pci_host_bridge since it's being 
>> applied to
>>       the entire host bridge per Mani's suggestion.
>>    -- During testing noticed that clkpm remained disabled and this was
>>       also handled by the formerly used pci_enable_link_state(). Add a
>>       check in pcie_clkpm_cap_init() as well to enable clkpm during init.
>>
>>   drivers/pci/pcie/aspm.c | 42 +++++++++++++++++++++++++++++++++++++++--
>>   include/linux/pci.h     |  9 +++++++++
>>   2 files changed, 49 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
>> index 919a05b97647..851ca3d68e55 100644
>> --- a/drivers/pci/pcie/aspm.c
>> +++ b/drivers/pci/pcie/aspm.c
>> @@ -373,6 +373,39 @@ static void pcie_set_clkpm(struct pcie_link_state 
>> *link, int enable)
>>       pcie_set_clkpm_nocheck(link, enable);
>>   }
>> +/**
>> + * pci_host_set_default_pcie_link_state - set controller-provided 
>> default ASPM/CLKPM mask
>> + * @host: host bridge on which to apply the defaults
>> + * @state: PCIE_LINK_STATE_XXX flags
>> + *
>> + * Allows a PCIe controller driver to specify the default ASPM and/or
>> + * Clock Power Management (CLKPM) link state mask that will be used
>> + * for links under this host bridge during ASPM/CLKPM capability init.
>> + *
>> + * The value is consumed in pcie_aspm_cap_init() and 
>> pcie_clkpm_cap_init()
>> + * to override the firmware-discovered defaults.
>> + *
>> + * Interpretation of aspm_default_link_state:
>> + *   - Nonzero: bitmask of PCIE_LINK_STATE_* values to be used as 
>> defaults
>> + *   - Zero:    no override provided; ASPM/CLKPM defaults fall back to
>> + *              values discovered in hardware/firmware
>> + *
>> + * Note: zero is always treated as "unset", not as "force ASPM/CLKPM 
>> off".
>> + */
>> +void pci_host_set_default_pcie_link_state(struct pci_host_bridge *host,
>> +                      unsigned int state)
>> +{
>> +    host->aspm_default_link_state = state;
>> +}
>> +EXPORT_SYMBOL_GPL(pci_host_set_default_pcie_link_state);
>> +
>> +static u32 pci_host_get_default_pcie_link_state(struct pci_dev *dev)
>> +{
>> +    struct pci_host_bridge *host = pci_find_host_bridge(dev->bus);
>> +
>> +    return host ? host->aspm_default_link_state : 0;
>> +}
>> +
>>   static void pcie_clkpm_cap_init(struct pcie_link_state *link, int 
>> blacklist)
>>   {
>>       int capable = 1, enabled = 1;
>> @@ -394,7 +427,10 @@ static void pcie_clkpm_cap_init(struct 
>> pcie_link_state *link, int blacklist)
>>               enabled = 0;
>>       }
>>       link->clkpm_enabled = enabled;
>> -    link->clkpm_default = enabled;
>> +    if (pci_host_get_default_pcie_link_state(link->pdev) & 
>> PCIE_LINK_STATE_CLKPM)
>> +        link->clkpm_default = 1;
>> +    else
>> +        link->clkpm_default = enabled;
>>       link->clkpm_capable = capable;
>>       link->clkpm_disable = blacklist ? 1 : 0;
>>   }
>> @@ -866,7 +902,9 @@ static void pcie_aspm_cap_init(struct 
>> pcie_link_state *link, int blacklist)
>>       }
>>       /* Save default state */
>> -    link->aspm_default = link->aspm_enabled;
>> +    link->aspm_default = pci_host_get_default_pcie_link_state(parent);
>> +    if (!link->aspm_default)
>> +        link->aspm_default = link->aspm_enabled;
>>       /* Setup initial capable state. Will be updated later */
>>       link->aspm_capable = link->aspm_support;
>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>> index 59876de13860..8947cbaf9fa6 100644
>> --- a/include/linux/pci.h
>> +++ b/include/linux/pci.h
>> @@ -620,6 +620,10 @@ struct pci_host_bridge {
>>       unsigned int    size_windows:1;        /* Enable root bus sizing */
>>       unsigned int    msi_domain:1;        /* Bridge wants MSI domain */
>> +#ifdef CONFIG_PCIEASPM
>> +    unsigned int    aspm_default_link_state;    /* Controller- 
>> provided default */
>> +#endif
>> +
>>       /* Resource alignment requirements */
>>       resource_size_t (*align_resource)(struct pci_dev *dev,
>>               const struct resource *res,
>> @@ -1849,6 +1853,8 @@ 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);
>>   int pci_enable_link_state_locked(struct pci_dev *pdev, int state);
>> +void pci_host_set_default_pcie_link_state(struct pci_host_bridge *host,
>> +                      unsigned int state);
>>   void pcie_no_aspm(void);
>>   bool pcie_aspm_support_enabled(void);
>>   bool pcie_aspm_enabled(struct pci_dev *pdev);
>> @@ -1861,6 +1867,9 @@ static inline int pci_enable_link_state(struct 
>> pci_dev *pdev, int state)
>>   { return 0; }
>>   static inline int pci_enable_link_state_locked(struct pci_dev *pdev, 
>> int state)
>>   { return 0; }
>> +static inline void
>> +pci_host_set_default_pcie_link_state(struct pci_host_bridge *host,
>> +                     unsigned int state) { }
>>   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; }
>>
>> base-commit: c17b750b3ad9f45f2b6f7e6f7f4679844244f0b9
> 

-- 
Kenneth R. Crudup / Sr. SW Engineer, Scott County Consulting, Orange 
County CA