linux-kernel - [RFC PATCH v2 1/4] PCI/ASPM: Remove struct pcie_link

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Date:   Wed, 29 Sep 2021 02:43:12 +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 1/4] PCI/ASPM: Remove struct pcie_link_state.parent

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

Information cached in struct pcie_link_state.parent is accessible
via struct pci_dev.

This patch:
 - removes *parent* from the *struct pcie_link_state*
 - creates pci_get_parent() which returns the parent of a pci_dev
 - replaces references to pcie_link_state.parent with a call to
   pci_get_parent()
 - removes BUG_ON(root->parent), instead uses the parent's root

Signed-off-by: Bolarinwa O. Saheed <refactormyself@...il.com>
---
 drivers/pci/pcie/aspm.c | 36 ++++++++++++++++++++++++++----------
 1 file changed, 26 insertions(+), 10 deletions(-)

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 013a47f587ce..414c04ffe962 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -50,7 +50,6 @@ struct pcie_link_state {
 	struct pci_dev *pdev;		/* Upstream component of the Link */
 	struct pci_dev *downstream;	/* Downstream component, function 0 */
 	struct pcie_link_state *root;	/* pointer to the root port link */
-	struct pcie_link_state *parent;	/* pointer to the parent Link state */
 	struct list_head sibling;	/* node in link_list */
 
 	/* ASPM state */
@@ -139,6 +138,14 @@ static int policy_to_clkpm_state(struct pcie_link_state *link)
 	return 0;
 }
 
+static struct pci_dev *pci_get_parent(struct pci_dev *pdev)
+{
+	if (!pdev || !pdev->bus->parent || !pdev->bus->parent->self)
+		return NULL;
+
+	return pdev->bus->parent->self;
+}
+
 static void pcie_set_clkpm_nocheck(struct pcie_link_state *link, int enable)
 {
 	struct pci_dev *child;
@@ -379,6 +386,7 @@ static void encode_l12_threshold(u32 threshold_us, u32 *scale, u32 *value)
 static void pcie_aspm_check_latency(struct pci_dev *endpoint)
 {
 	u32 latency, l1_switch_latency = 0;
+	struct pci_dev *parent;
 	struct aspm_latency *acceptable;
 	struct pcie_link_state *link;
 
@@ -419,7 +427,8 @@ static void pcie_aspm_check_latency(struct pci_dev *endpoint)
 			link->aspm_capable &= ~ASPM_STATE_L1;
 		l1_switch_latency += 1000;
 
-		link = link->parent;
+		parent = pci_get_parent(link->pdev);
+		link = parent ? parent->link_state : NULL;
 	}
 }
 
@@ -793,9 +802,11 @@ static void pcie_config_aspm_link(struct pcie_link_state *link, u32 state)
 
 static void pcie_config_aspm_path(struct pcie_link_state *link)
 {
+	struct pci_dev *parent;
 	while (link) {
 		pcie_config_aspm_link(link, policy_to_aspm_state(link));
-		link = link->parent;
+		parent = pci_get_parent(link->pdev);
+		link = parent ? parent->link_state : NULL;
 	}
 }
 
@@ -864,16 +875,15 @@ static struct pcie_link_state *alloc_pcie_link_state(struct pci_dev *pdev)
 	    !pdev->bus->parent->self) {
 		link->root = link;
 	} else {
-		struct pcie_link_state *parent;
+		struct pci_dev *parent;
 
-		parent = pdev->bus->parent->self->link_state;
-		if (!parent) {
+		parent = pci_get_parent(pdev);
+		if (!parent->link_state) {
 			kfree(link);
 			return NULL;
 		}
 
-		link->parent = parent;
-		link->root = link->parent->root;
+		link->root = parent->link_state->root;
 	}
 
 	list_add(&link->sibling, &link_list);
@@ -962,7 +972,11 @@ void pcie_aspm_init_link_state(struct pci_dev *pdev)
 static void pcie_update_aspm_capable(struct pcie_link_state *root)
 {
 	struct pcie_link_state *link;
-	BUG_ON(root->parent);
+	struct pci_dev *parent = pci_get_parent(root->pdev);
+
+	if (parent && parent->link_state)
+		root = parent->link_state->root;
+
 	list_for_each_entry(link, &link_list, sibling) {
 		if (link->root != root)
 			continue;
@@ -985,6 +999,7 @@ static void pcie_update_aspm_capable(struct pcie_link_state *root)
 /* @pdev: the endpoint device */
 void pcie_aspm_exit_link_state(struct pci_dev *pdev)
 {
+	struct pci_dev *parent_dev;
 	struct pci_dev *parent = pdev->bus->self;
 	struct pcie_link_state *link, *root, *parent_link;
 
@@ -1002,7 +1017,8 @@ void pcie_aspm_exit_link_state(struct pci_dev *pdev)
 
 	link = parent->link_state;
 	root = link->root;
-	parent_link = link->parent;
+	parent_dev = pci_get_parent(link->pdev);
+	parent_link = parent_dev ? parent_dev->link_state : NULL;
 
 	/* All functions are removed, so just disable ASPM for the link */
 	pcie_config_aspm_link(link, 0);
-- 
2.20.1