On Mon, Aug 09, 2021 at 01:59:01PM -0500, Bjorn Helgaas wrote: > On Tue, Aug 03, 2021 at 12:06:44PM -0500, Bjorn Helgaas wrote: > > On Sat, Jul 24, 2021 at 05:30:02PM +0800, Huacai Chen wrote: > > > On Sat, Jul 24, 2021 at 8:10 AM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > > > Thanks for the above; that was helpful. To summarize: > > > > > > > > - On your system, the AST2500 bridge [1a03:1150] does not implement > > > > PCI_BRIDGE_CTL_VGA [1]. This is perfectly legal but means the > > > > legacy VGA resources won't reach downstream devices unless they're > > > > included in the usual bridge windows. > > > > > > > > - vga_arb_select_default_device() will set a device below such a > > > > bridge as the default VGA device as long as it has PCI_COMMAND_IO > > > > and PCI_COMMAND_MEMORY enabled. > > > > > > > > - vga_arbiter_add_pci_device() is called for every VGA device, > > > > either at boot-time or at hot-add time, and it will also set the > > > > device as the default VGA device, but ONLY if all bridges leading > > > > to it implement PCI_BRIDGE_CTL_VGA. > > > > > > > > - This difference between vga_arb_select_default_device() and > > > > vga_arbiter_add_pci_device() means that a device below an AST2500 > > > > or similar bridge can only be set as the default if it is > > > > enumerated before vga_arb_device_init(). > > > > > > > > - On ACPI-based systems, PCI devices are enumerated by acpi_init(), > > > > which runs before vga_arb_device_init(). > > > > > > > > - On non-ACPI systems, like your MIPS system, they are enumerated by > > > > pcibios_init(), which typically runs *after* > > > > vga_arb_device_init(). > > > > > > > > So I think the critical change is actually that you made > > > > vga_arb_update_default_device(), which you call from > > > > vga_arbiter_add_pci_device(), set the default device even if it does > > > > not own the VGA resources because an upstream bridge doesn't implement > > > > PCI_BRIDGE_CTL_VGA, i.e., > > > > > > > > (vgadev->owns & VGA_RSRC_LEGACY_MASK) != VGA_RSRC_LEGACY_MASK > > > > > > > > Does that seem right? > > > > > > Yes, that's right. > > > > I think that means I screwed up. I somehow had it in my head that the > > hot-add path would never set the default VGA device. But that is > > false. > > > > I still think we should move vgaarb.c to drivers/pci/ and get it more > > tightly integrated into the PCI core. > > > > BUT that's a lot of churn and obscures the simple change that fixes > > the problem for you. So I think the first step should be the change > > to vga_arb_update_default_device() so it sets the default device even > > when the upstream bridge doesn't implement PCI_BRIDGE_CTL_VGA. > > > > That should be a relatively small change, and I think it's better to > > make the fix before embarking on major restructuring. > > To make sure this doesn't get lost: I'm hoping you can separate out > and post the small patch to vga_arb_update_default_device(). > > I can look at the move/restructure stuff later. What's happening with this? I'm still assuming you can post a small patch to vga_arb_update_default_device() that's suitable for v5.15, Huacai. Otherwise I'm afraid we won't make any forward progress this cycle. Bjorn
