[PATCH v3 2/8] PCI/ASPM: Add pci_force_enable_link_state() API

[Manivannan Sadhasivam]

From: Manivannan Sadhasivam <manivannan.sadhasivam at oss.qualcomm.com>

pci_enable_link_state() and pci_enable_link_state_locked() APIs only enable
the ASPM states that were not previously disabled via
pci_disable_link_state*() API or blacklisted during init (e.g. the pre-1.1
device blacklist, which is only meant to be overridden with
'pcie_aspm=force'). This is an intentional behavior as these APIs must not
silently re-enable states that were deliberately disabled, since doing so
could enable ASPM on a link where it is known to be unsafe.

However, some drivers (e.g. the atheros WLAN drivers) save the currently
enabled ASPM states, disable all ASPM states before firmware download, and
then try to restore exactly the states that were enabled before. Restoring
those states requires re-enabling states that were just disabled via
pci_disable_link_state() API. But, this cannot be achieved using the
existing APIs.

Hence, add pci_force_enable_link_state() API for such callers. Unlike
pci_enable_link_state(), it re-enables the requested states even if they
were previously disabled via pci_disable_link_state() or disabled during
init. The caller is therefore responsible for only enabling states the
device actually supports, typically the ones previously reported by
pcie_aspm_enabled().

This API is implemented by adding a 'force' parameter to the shared
__pci_enable_link_state() helper. When 'force' is true, the requested
states are cleared from 'link->aspm_disable' before enabling.

Suggested-by: Ilpo Järvinen <ilpo.jarvinen at linux.intel.com>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam at oss.qualcomm.com>
---
 drivers/pci/pcie/aspm.c | 37 ++++++++++++++++++++++++++++++++++---
 include/linux/pci.h     |  3 +++
 2 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 1c15a14718e8..c04fb71de91c 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -1506,7 +1506,8 @@ int pci_disable_link_state(struct pci_dev *pdev, int state)
 }
 EXPORT_SYMBOL(pci_disable_link_state);
 
-static int __pci_enable_link_state(struct pci_dev *pdev, int state, bool locked)
+static int __pci_enable_link_state(struct pci_dev *pdev, int state, bool locked,
+				   bool force)
 {
 	struct pcie_link_state *link = pcie_aspm_get_link(pdev);
 
@@ -1527,6 +1528,10 @@ static int __pci_enable_link_state(struct pci_dev *pdev, int state, bool locked)
 		down_read(&pci_bus_sem);
 	mutex_lock(&aspm_lock);
 	link->aspm_default = pci_calc_aspm_enable_mask(state);
+
+	/* Force enable states that were previously disabled */
+	if (force)
+		link->aspm_disable &= ~link->aspm_default;
 	pcie_config_aspm_link(link, policy_to_aspm_state(link));
 
 	link->clkpm_default = (state & PCIE_LINK_STATE_CLKPM) ? 1 : 0;
@@ -1553,7 +1558,7 @@ static int __pci_enable_link_state(struct pci_dev *pdev, int state, bool locked)
  */
 int pci_enable_link_state(struct pci_dev *pdev, int state)
 {
-	return __pci_enable_link_state(pdev, state, false);
+	return __pci_enable_link_state(pdev, state, false, false);
 }
 EXPORT_SYMBOL(pci_enable_link_state);
 
@@ -1576,10 +1581,36 @@ int pci_enable_link_state_locked(struct pci_dev *pdev, int state)
 {
 	lockdep_assert_held_read(&pci_bus_sem);
 
-	return __pci_enable_link_state(pdev, state, true);
+	return __pci_enable_link_state(pdev, state, true, false);
 }
 EXPORT_SYMBOL(pci_enable_link_state_locked);
 
+/**
+ * pci_force_enable_link_state - Force enable device link state
+ * @pdev: PCI device
+ * @state: Mask of ASPM link states to enable
+ *
+ * Enable device link state, so the link will enter the specified states.
+ * Unlike pci_enable_link_state(), this also re-enables states previously
+ * disabled by pci_disable_link_state() and overrides the ASPM states disabled
+ * during init (e.g., the pre-1.1 device blacklist). The caller is therefore
+ * responsible for only enabling states the device supports, typically the ones
+ * previously reported by pcie_aspm_enabled().
+ *
+ * Note that if the BIOS didn't grant ASPM control to the OS, this does nothing
+ * because we can't touch the LNKCTL register.
+ *
+ * Note: Ensure devices are in D0 before enabling PCI-PM L1 PM Substates, per
+ * PCIe r6.0, sec 5.5.4.
+ *
+ * Return: 0 on success, a negative errno otherwise.
+ */
+int pci_force_enable_link_state(struct pci_dev *pdev, int state)
+{
+	return __pci_enable_link_state(pdev, state, false, true);
+}
+EXPORT_SYMBOL(pci_force_enable_link_state);
+
 void pcie_aspm_remove_cap(struct pci_dev *pdev, u32 lnkcap)
 {
 	if (lnkcap & PCI_EXP_LNKCAP_ASPM_L0S)
diff --git a/include/linux/pci.h b/include/linux/pci.h
index ebb5b9d76360..be6719626c8f 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1918,6 +1918,7 @@ 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);
+int pci_force_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);
@@ -1930,6 +1931,8 @@ 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 int pci_force_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; }

-- 
2.43.0