linux-kernel - [PATCH 2/6] PCI/VGA: Deal with PCI VGA compatible devices only

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Message-Id: <20230711134354.755966-3-sui.jingfeng@linux.dev>
Date:   Tue, 11 Jul 2023 21:43:50 +0800
From:   Sui Jingfeng <sui.jingfeng@...ux.dev>
To:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, Sui@...r.kernel.org,
        Jingfeng@...ngson.cn
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, loongson-kernel@...ts.loongnix.cn,
        Sui Jingfeng <suijingfeng@...ngson.cn>,
        Mario Limonciello <mario.limonciello@....com>
Subject: [PATCH 2/6] PCI/VGA: Deal with PCI VGA compatible devices only

From: Sui Jingfeng <suijingfeng@...ngson.cn>

Currently, vgaarb only cares about PCI VGA-compatible class devices.

While vga_arbiter_del_pci_device() gets called unbalanced when some PCI
device is about to be removed. This happens even during the boot process.

Another reason is that the vga_arb_device_init() function is not efficient.
Since we only care about VGA-compatible devices (pdev->class == 0x030000),
We could filter the unqualified devices out in the vga_arb_device_init()
function. While the current implementation is to search all PCI devices
in a system, this is not necessary.

Reviewed-by: Mario Limonciello <mario.limonciello@....com>
Signed-off-by: Sui Jingfeng <suijingfeng@...ngson.cn>
---
 drivers/pci/vgaarb.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
index c1bc6c983932..021116ed61cb 100644
--- a/drivers/pci/vgaarb.c
+++ b/drivers/pci/vgaarb.c
@@ -754,10 +754,6 @@ static bool vga_arbiter_add_pci_device(struct pci_dev *pdev)
 	struct pci_dev *bridge;
 	u16 cmd;
 
-	/* Only deal with VGA class devices */
-	if ((pdev->class >> 8) != PCI_CLASS_DISPLAY_VGA)
-		return false;
-
 	/* Allocate structure */
 	vgadev = kzalloc(sizeof(struct vga_device), GFP_KERNEL);
 	if (vgadev == NULL) {
@@ -1502,6 +1498,10 @@ static int pci_notify(struct notifier_block *nb, unsigned long action,
 
 	vgaarb_dbg(dev, "%s\n", __func__);
 
+	/* Deal with VGA compatible devices only */
+	if ((pdev->class >> 8) != PCI_CLASS_DISPLAY_VGA)
+		return 0;
+
 	/* For now we're only intereted in devices added and removed. I didn't
 	 * test this thing here, so someone needs to double check for the
 	 * cases of hotplugable vga cards. */
@@ -1534,8 +1534,8 @@ static struct miscdevice vga_arb_device = {
 
 static int __init vga_arb_device_init(void)
 {
+	struct pci_dev *pdev = NULL;
 	int rc;
-	struct pci_dev *pdev;
 
 	rc = misc_register(&vga_arb_device);
 	if (rc < 0)
@@ -1543,13 +1543,14 @@ static int __init vga_arb_device_init(void)
 
 	bus_register_notifier(&pci_bus_type, &pci_notifier);
 
-	/* We add all PCI devices satisfying VGA class in the arbiter by
-	 * default */
-	pdev = NULL;
-	while ((pdev =
-		pci_get_subsys(PCI_ANY_ID, PCI_ANY_ID, PCI_ANY_ID,
-			       PCI_ANY_ID, pdev)) != NULL)
-		vga_arbiter_add_pci_device(pdev);
+	/*
+	 * We add all PCI VGA compatible devices in the arbiter by default
+	 */
+	do {
+		pdev = pci_get_class(PCI_CLASS_DISPLAY_VGA << 8, pdev);
+		if (pdev)
+			vga_arbiter_add_pci_device(pdev);
+	} while (pdev);
 
 	pr_info("loaded\n");
 	return rc;
-- 
2.25.1