Hi Daniel many thanks for your patch > -----Original Message----- > From: Daniel Axtens [mailto:dja@xxxxxxxxxx] > Sent: 19 July 2017 03:15 > To: linux-pci@xxxxxxxxxxxxxxx; linuxppc-dev@xxxxxxxxxxxxxxxx; linux- > arm-kernel@xxxxxxxxxxxxxxxxxxx > Cc: benh@xxxxxxxxxxxxxxxxxxx; Liuxinliang (Matthew Liu); > zourongrong@xxxxxxxxx; catalin.marinas@xxxxxxx; will.deacon@xxxxxxx; > Gabriele Paoloni; bhelgaas@xxxxxxxxxx; airlied@xxxxxxxx; > daniel.vetter@xxxxxxxxx; alex.williamson@xxxxxxxxxx; Daniel Axtens > Subject: [PATCH v2 0/4] Allow non-legacy cards to be vgaarb default > > [v2, in which I send the right patches. My apologies to you all.] > > Hi all, > > Previously I posted a patch that provided a quirk for a hibmc card > behind a particular Huawei bridge that allowed it to be marked as the > default device in the VGA arbiter.[0] This lead to some discussion.[1] > It was broadly suggested that a more generic solution would be better, > something in the style of powerpc's fixup_vga() quirk. > > Here is my suggested solution: > > - Create a Kconfig option ARCH_WANT_VGA_ARB_FALLBACK and In my opinion we could avoid depending on a Kernel config options. I.e. we can have generic code that, after all PCI devs are enumerated: 1) check if we have a default vga device 2) if not check each registered PCI device and make default device the first one that is a VGA device, capable to respond to IO and MEM requests and that has a driver bound to it > > - if an arch selects that option, install PCI_FIXUP_CLASS_ENABLE > hook. This hook fires when a card is enabled, which will require > that a driver has been bound. > > - if there is no default device when the hook fires, and the device > can control memory and I/O, mark it as default. I am worried that the patchset you proposed has a race condition with the VGA arbiter. In fact you see: subsys_initcall(vga_arb_device_init) is not guaranteed to be called before subsys_initcall(acpi_init) acpi_init->acpi_scan_init->acpi_pci_root_init() at this stage the PCI enumeration is done and as soon as a device is added the Kernel will look for a driver to bind to it and therefore you quirk could be called before the VGA arbiter... Do you agree? What about modifying vgaarb.c to add a late_initcall() checking what I suggested above? Thanks Gab [...]
