On Thu, Aug 21, 2025 at 08:11:57PM -0700, 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@xxxxxxxxxxxxxxx> > --- Besides the review I'd appreciate a Tested-by on this patch. Thanks. David > > 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. > > 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. > > 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..b4f0b4805a35 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 *parent) > +{ > + struct pci_host_bridge *host = pci_find_host_bridge(parent->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 > -- > 2.43.0 > >
