PCI/ASPM: Stop caching device L0s, L1 acceptable exit latencies

Previously we calculated the device's acceptable L0s and L1 exit latencies
in pcie_aspm_cap_init() and cached them in struct pcie_link_state.

These values are only used in pcie_aspm_check_latency() where they are
compared with the actual exit latencies of the link.  This path is used
when removing or changing the D state of the device, so it's relatively low
frequency.

To reduce the amount of per-link data we store, remove the acceptable[]
arrays from struct pcie_link_state and calculate them directly from the
already-cached Device Capabilities register when needed.

[bhelgaas: use endpoint->devcap instead of reading it again]
Link: https://lore.kernel.org/r/20211119193732.12343-4-refactormyself@gmail.com
Signed-off-by: Saheed O. Bolarinwa <refactormyself@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

Author: refactormyself

drivers/pci/pcie/aspm.c

@@ -65,12 +65,6 @@ struct pcie_link_state {
 	u32 clkpm_enabled:1;		/* Current Clock PM state */
 	u32 clkpm_default:1;		/* Default Clock PM state by BIOS */
 	u32 clkpm_disable:1;		/* Clock PM disabled */
-
-	/*
-	 * Endpoint acceptable latencies. A pcie downstream port only
-	 * has one slot under it, so at most there are 8 functions.
-	 */
-	struct aspm_latency acceptable[8];
 };
 
 static int aspm_disabled, aspm_force;
@@ -389,7 +383,8 @@ static void encode_l12_threshold(u32 threshold_us, u32 *scale, u32 *value)
 
 static void pcie_aspm_check_latency(struct pci_dev *endpoint)
 {
-	u32 latency, lnkcap_up, lnkcap_dw, l1_switch_latency = 0;
+	u32 latency, encoding, lnkcap_up, lnkcap_dw;
+	u32 l1_switch_latency = 0;
 	struct aspm_latency latency_up, latency_dw;
 	struct aspm_latency *acceptable;
 	struct pcie_link_state *link;
@@ -400,7 +395,14 @@ static void pcie_aspm_check_latency(struct pci_dev *endpoint)
 		return;
 
 	link = endpoint->bus->self->link_state;
-	acceptable = &link->acceptable[PCI_FUNC(endpoint->devfn)];
+
+	/* Calculate endpoint L0s acceptable latency */
+	encoding = (endpoint->devcap & PCI_EXP_DEVCAP_L0S) >> 6;
+	acceptable->l0s = calc_l0s_acceptable(encoding);
+
+	/* Calculate endpoint L1 acceptable latency */
+	encoding = (endpoint->devcap & PCI_EXP_DEVCAP_L1) >> 9;
+	acceptable->l1 = calc_l1_acceptable(encoding);
 
 	while (link) {
 		struct pci_dev *dev = pci_function_0(link->pdev->subordinate);
@@ -666,22 +668,11 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
 
 	/* Get and check endpoint acceptable latencies */
 	list_for_each_entry(child, &linkbus->devices, bus_list) {
-		u32 reg32, encoding;
-		struct aspm_latency *acceptable =
-			&link->acceptable[PCI_FUNC(child->devfn)];
 
 		if (pci_pcie_type(child) != PCI_EXP_TYPE_ENDPOINT &&
 		    pci_pcie_type(child) != PCI_EXP_TYPE_LEG_END)
 			continue;
 
-		pcie_capability_read_dword(child, PCI_EXP_DEVCAP, &reg32);
-		/* Calculate endpoint L0s acceptable latency */
-		encoding = (reg32 & PCI_EXP_DEVCAP_L0S) >> 6;
-		acceptable->l0s = calc_l0s_acceptable(encoding);
-		/* Calculate endpoint L1 acceptable latency */
-		encoding = (reg32 & PCI_EXP_DEVCAP_L1) >> 9;
-		acceptable->l1 = calc_l1_acceptable(encoding);
-
 		pcie_aspm_check_latency(child);
 	}
 }