[PATCH v6 2/3] PCI/ASPM: Disable/restore ASPM on every function for multi-function devices

[Krishna Chaitanya Chundru]

pcie_aspm_cap_init() disables ASPM L0s/L1 before touching L1SS config,
then restores the pre-existing state afterward. Both steps only ever
touched link->downstream, i.e. function 0 of the downstream component,
leaving sibling functions (>0) on a multi-function device untouched.

This means the "disable" step does not actually disable ASPM link-wide
on a multi-function device: a sibling function can still have L1
enabled even after this step runs. PCIe r6.2 sec 7.5.3.7 recommends
programming the same ASPM Control value for all functions of a
multi-function device, and pcie_config_aspm_link() already loops over
every function on the bus for exactly this reason.

Loop over every function on linkbus->devices for both the disable and
restore steps, keeping the existing PCIe r6.2 sec 7.5.3.7 ordering
(disable downstream functions before upstream, restore upstream before
downstream functions). The masked pcie_capability_clear_and_set_word()
accessor from the previous commit makes this safe: it only ever
touches the ASPM Control bits, so function-specific bits elsewhere in
LNKCTL (e.g. Read Completion Boundary, CLKREQ Enable) on sibling
functions are left untouched.

Fixes: 7447990137bf ("PCI/ASPM: Disable L1 before disabling L1 PM Substates")
Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@xxxxxxxxxxxxxxxx>
---
 drivers/pci/pcie/aspm.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 3f9c0f9a1cc7..544f35bb2555 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -861,6 +861,7 @@ static void pcie_aspm_override_default_link_state(struct pcie_link_state *link)
 static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
 {
 	struct pci_dev *child = link->downstream, *parent = link->pdev;
+	struct pci_dev *fn;
 	u16 parent_lnkctl, child_lnkctl;
 	struct pci_bus *linkbus = parent->subordinate;
 
@@ -894,8 +895,9 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
 	/* Disable L0s/L1 before updating L1SS config */
 	if (FIELD_GET(PCI_EXP_LNKCTL_ASPMC, child_lnkctl) ||
 	    FIELD_GET(PCI_EXP_LNKCTL_ASPMC, parent_lnkctl)) {
-		pcie_capability_clear_and_set_word(child, PCI_EXP_LNKCTL,
-						   PCI_EXP_LNKCTL_ASPMC, 0);
+		list_for_each_entry(fn, &linkbus->devices, bus_list)
+			pcie_capability_clear_and_set_word(fn, PCI_EXP_LNKCTL,
+							   PCI_EXP_LNKCTL_ASPMC, 0);
 		pcie_capability_clear_and_set_word(parent, PCI_EXP_LNKCTL,
 						   PCI_EXP_LNKCTL_ASPMC, 0);
 	}
@@ -930,9 +932,10 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
 		pcie_capability_clear_and_set_word(parent, PCI_EXP_LNKCTL,
 						   PCI_EXP_LNKCTL_ASPMC,
 						   parent_lnkctl & PCI_EXP_LNKCTL_ASPMC);
-		pcie_capability_clear_and_set_word(child, PCI_EXP_LNKCTL,
-						   PCI_EXP_LNKCTL_ASPMC,
-						   child_lnkctl & PCI_EXP_LNKCTL_ASPMC);
+		list_for_each_entry(fn, &linkbus->devices, bus_list)
+			pcie_capability_clear_and_set_word(fn, PCI_EXP_LNKCTL,
+							   PCI_EXP_LNKCTL_ASPMC,
+							   child_lnkctl & PCI_EXP_LNKCTL_ASPMC);
 	}
 
 	/* Save default state */

-- 
2.34.1