Hi, On 2023/7/17 17:51, suijingfeng wrote: > > Hi, > > > On 2023/7/11 21:43, Sui Jingfeng wrote: >> From: Sui Jingfeng >> >> 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 >> Signed-off-by: Sui Jingfeng >> --- >> 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); > I suddenly remember one more thing that I forget to explain. > > In a previous thread[1] of previous version of this series, > > Maciej seems argue that PCI_CLASS_NOT_DEFINED_VGA should be handled also. > > But, even I try to handled PCI_CLASS_NOT_DEFINED_VGA at here, > > this card still will not be annotate as boot_vga, > > because the pci_dev_attrs_are_visible() function only consider VGA compatible devices > > which (pdev->class >> 8 == PCI_CLASS_DISPLAY_VGA) is true. See [2]. > > > Intel integrated GPU is more intelligent, > > which could change their class of the PCI(e) device to 0x038000 when > > multiple GPU co-exist. Even though the GPU can display. This is configurable by > > the firmware, but this is trying to escape the arbitration by changing is PCI id. "by changing is PCI id" -> "by changing its PCI(e) class number". For example, the intel GPU will change their PCI class number from 0x030000 to 0x038000, if a user choose the dGPU as primary by setting their UEFI firmware from the BIOS. But other GPUs may not support to change their PCI class number. > > So, PCI devices belong to the PCI_CLASS_DISPLAY_OTHER, PCI_CLASS_DISPLAY_3D and PCI_CLASS_DISPLAY_XGA > > can not participate in the arbitration. They are all will be get filtered. I means that PCI devices with their PCI class number equal  to PCI_CLASS_DISPLAY_OTHER, PCI_CLASS_DISPLAY_3D and PCI_CLASS_DISPLAY_XGA will get ignored by vgaarb currently. Even we throw other devices(DISPLAY_OTHER, DISPLAY_3D, DISPLAY_XGA) into the arbitrator, We still not make a meaningful progress, I need also to change the code in link [2] to make the boot_vga visible to userspace. Because X server is the end consumer. This already form an ABI.  So change the code here alone is not enough to expand vgaarb. > > So, this is a limitation of the vgaarb itself. > > While I could help to improve it in the future, what do you think? > Is my express clear? Am I express my thoughts clearly ? > > [1] > https://lkml.kernel.org/nouveau/alpine.DEB.2.21.2306190339590.14084@angie.orcam.me.uk/#t > > [2] > https://elixir.bootlin.com/linux/latest/source/drivers/pci/pci-sysfs.c#L1544 > Alex acclaims that "we won't need vgaarb if the platform has no VGA devices", see [3]. while this is not 100% correct, because X server is the primary consumer of the boot_vga flag, the convention usage of the userspace and the kernel space is already established. So without we can craft something new easily without significant change. [3]https://lkml.kernel.org/nouveau/CADnq5_PFoM2O8mCd6+VFfu9Nc-Hg_HTnwEMxrq0FGRpva1kKiA@mail.gmail.com/ >> >> pr_info("loaded\n"); >> return rc;