On Sat, Jun 05, 2021 at 10:02:05AM +0800, Huacai Chen wrote:
On Sat, Jun 5, 2021 at 3:56 AM Bjorn Helgaas helgaas@kernel.org wrote:
On Fri, Jun 04, 2021 at 12:50:03PM +0800, Huacai Chen wrote:
On Thu, Jun 3, 2021 at 2:31 AM Bjorn Helgaas bhelgaas@google.com wrote:
I think the simplest solution, which I suggested earlier [1], would be to explicitly call vga_arbiter_add_pci_device() directly from the PCI core when it enumerates a VGA device. Then there's no initcall and no need for the BUS_NOTIFY_ADD/DEL_DEVICE stuff. vga_arbiter_add_pci_device() could set the default VGA device when it is enumerated, and change the default device if we enumerate a "better" one. And hotplug VGA devices would work automatically.
Emm, It seems that your solution has some difficulties to remove the whole initcall(vga_arb_device_init): we call vga_arbiter_add_pci_device() in pci_bus_add_device(), the list_for_each_entry() loop can be moved to vga_arbiter_check_bridge_sharing(), vga_arb_select_default_device() can be renamed to vga_arb_update_default_device() and be called in vga_arbiter_add_pci_device(), but how to handle misc_register(&vga_arb_device)?
Might need to keep vga_arb_device_init() as an initcall, but remove everything from it except the misc_register().
OK, let me try. But I think call vga_arbiter_add_pci_device() in pci core is nearly the same as notifier. Anyway, I will send a new patch later.
Notifiers are useful in some situations, for example, if a loadable module needs to be called when a device is added or removed.
But when possible, I will always choose a direct call instead because it's much less complicated. The VGA arbiter cannot be a loadable module, so I don't think there's any reason to use a notifier in this case.
Bjorn