linux-kernel - [RFC PATCH v2 4/4] PCI/ASPM: Remove unncessary linked list from aspm.c

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Message-Id: <20210929004315.22558-5-refactormyself@gmail.com>
Date:   Wed, 29 Sep 2021 02:43:15 +0200
From:   "Saheed O. Bolarinwa" <refactormyself@...il.com>
To:     helgaas@...nel.org
Cc:     "Bolarinwa O. Saheed" <refactormyself@...il.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH v2 4/4] PCI/ASPM: Remove unncessary linked list from aspm.c

From: "Bolarinwa O. Saheed" <refactormyself@...il.com>

aspm.c defines a linked list - `link_list` and stores each of
its node in struct pcie_link_state.sibling. This linked list
tracks devices for which the struct pcie_link_state object
was successfully created. It is used to loop through the list
for instance to set ASPM policy or update changes. However, it
is possible to access these devices via existing lists defined
inside pci.h

This patch:
- removes link_list and struct pcie_link_state.sibling
- accesses child devices via struct pci_dev.bust_list
- accesses all PCI buses via pci_root_buses on struct pci_bus.node

Signed-off-by: Bolarinwa O. Saheed <refactormyself@...il.com>
---
 drivers/pci/pcie/aspm.c | 39 +++++++++++++++++++++------------------
 1 file changed, 21 insertions(+), 18 deletions(-)

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 56d4fe7d50b5..4bef652dc63c 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -48,7 +48,6 @@ struct aspm_latency {
 
 struct pcie_link_state {
 	struct pci_dev *pdev;		/* Upstream component of the Link */
-	struct list_head sibling;	/* node in link_list */
 
 	/* ASPM state */
 	u32 aspm_support:7;		/* Supported ASPM state */
@@ -76,7 +75,6 @@ struct pcie_link_state {
 static int aspm_disabled, aspm_force;
 static bool aspm_support_enabled = true;
 static DEFINE_MUTEX(aspm_lock);
-static LIST_HEAD(link_list);
 
 #define POLICY_DEFAULT 0	/* BIOS default setting */
 #define POLICY_PERFORMANCE 1	/* high performance */
@@ -880,10 +878,7 @@ static struct pcie_link_state *alloc_pcie_link_state(struct pci_dev *pdev)
 	if (!link)
 		return NULL;
 
-	INIT_LIST_HEAD(&link->sibling);
 	link->pdev = pdev;
-
-	list_add(&link->sibling, &link_list);
 	pdev->link_state = link;
 	return link;
 }
@@ -970,24 +965,22 @@ static void pcie_update_aspm_capable(struct pcie_link_state *root)
 {
 	struct pcie_link_state *link;
 	struct pci_dev *dev, *root_dev;
+	struct pci_bus *rootbus = root->pdev->bus;
 
 	/* Ensure it is the root device */
 	root_dev = pcie_get_root(root->pdev);
 	root = root_dev ? root_dev->link_state : NULL;
 
-	list_for_each_entry(link, &link_list, sibling) {
-		dev = pcie_get_root(link->pdev);
-		if (dev->link_state != root)
+	list_for_each_entry(dev, &rootbus->devices, bus_list) {
+		if (!dev->link_state)
 			continue;
 
-		link->aspm_capable = link->aspm_support;
+		dev->link_state->aspm_capable = link->aspm_support;
 	}
-	list_for_each_entry(link, &link_list, sibling) {
+
+	list_for_each_entry(dev, &rootbus->devices, bus_list) {
 		struct pci_dev *child;
-		struct pci_bus *linkbus = link->pdev->subordinate;
-		dev = pcie_get_root(link->pdev);
-		if (dev->link_state != root)
-			continue;
+		struct pci_bus *linkbus = dev->subordinate;
 
 		list_for_each_entry(child, &linkbus->devices, bus_list) {
 			if ((pci_pcie_type(child) != PCI_EXP_TYPE_ENDPOINT) &&
@@ -1024,7 +1017,6 @@ void pcie_aspm_exit_link_state(struct pci_dev *pdev)
 
 	/* All functions are removed, so just disable ASPM for the link */
 	pcie_config_aspm_link(link, 0);
-	list_del(&link->sibling);
 	/* Clock PM is for endpoint device */
 	free_link_state(link);
 
@@ -1164,6 +1156,8 @@ static int pcie_aspm_set_policy(const char *val,
 {
 	int i;
 	struct pcie_link_state *link;
+	struct pci_bus *bus;
+	struct pci_dev *pdev;
 
 	if (aspm_disabled)
 		return -EPERM;
@@ -1176,9 +1170,18 @@ static int pcie_aspm_set_policy(const char *val,
 	down_read(&pci_bus_sem);
 	mutex_lock(&aspm_lock);
 	aspm_policy = i;
-	list_for_each_entry(link, &link_list, sibling) {
-		pcie_config_aspm_link(link, policy_to_aspm_state(link));
-		pcie_set_clkpm(link, policy_to_clkpm_state(link));
+	list_for_each_entry(bus, &pci_root_buses, node) {
+		list_for_each_entry(pdev, &bus->devices, bus_list) {
+			if (!pci_is_pcie(pdev))
+				break;
+
+			link = pdev->link_state;
+			if (!link)
+				continue;
+
+			pcie_config_aspm_link(link, policy_to_aspm_state(link));
+			pcie_set_clkpm(link, policy_to_clkpm_state(link));
+		}
 	}
 	mutex_unlock(&aspm_lock);
 	up_read(&pci_bus_sem);
-- 
2.20.1