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Message-ID: <20250822031159.4005529-1-david.e.box@linux.intel.com>
Date: Thu, 21 Aug 2025 20:11:57 -0700
From: "David E. Box" <david.e.box@...ux.intel.com>
To: rafael@...nel.org,
bhelgaas@...gle.com,
vicamo.yang@...onical.com,
kenny@...ix.com,
ilpo.jarvinen@...ux.intel.com,
nirmal.patel@...ux.intel.com,
mani@...nel.org
Cc: "David E. Box" <david.e.box@...ux.intel.com>,
linux-pm@...r.kernel.org,
linux-pci@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH V2 1/2] PCI/ASPM: Add host-bridge API to override default ASPM/CLKPM link state
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@...ux.intel.com>
---
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
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