Re: [PATCH 2/6] PCI/VGA: Deal with PCI VGA compatible devices only

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Hi,


On 2023/7/20 02:26, Bjorn Helgaas wrote:
On Tue, Jul 11, 2023 at 09:43:50PM +0800, Sui Jingfeng wrote:
[...]
Reviewed-by: Mario Limonciello <mario.limonciello@xxxxxxx>
Signed-off-by: Sui Jingfeng <suijingfeng@xxxxxxxxxxx>
I do not see Mario's Reviewed-by on the list.  I do see Mario's
Reviewed-by [2] for a previous version, but that version added this in
pci_notify():

   + if (pdev->class != PCI_CLASS_DISPLAY_VGA << 8)
   +   return 0;

while this version adds:

   + if ((pdev->class >> 8) != PCI_CLASS_DISPLAY_VGA)
   +   return 0;

It's OK to carry a review to future versions if there are
insignificant changes, but this is a functional change that seems
significant to me.  The first matches only 0x030000, while the second
discards the low eight bits so it matches 0x0300XX.

Yes, you are right.

But I suddenly realized that this may deserve another patch, desperate trivial.

What this version adds here is *same* before this patch set is applied.

My explanation about the minor tweak being made before this version and previous version

is that  I want to keep my patch *less distraction*.

The major functional gains(benefit) is that we filter non VGA compatible devices out.

As a start point, I should keep one patch do one thing (do one thing and do it well).


On the other hand, even though the lest significant 8 but if pdev->class is really matter.

I think I still need to wait the things(a bug emerged, for example) became clear.

Instead of cleanup all potential problems with obvious motivation.

I think Mario will accept my explanation.

[1] https://lore.kernel.org/r/20230718231400.GA496927@bhelgaas
[2] https://lore.kernel.org/all/5b6fdf65-b354-94a9-f883-be820157efad@xxxxxxx/

---
  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




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