Hi, Bjorn,
On Wed, Sep 15, 2021 at 3:18 AM Bjorn Helgaas helgaas@kernel.org wrote:
On Sat, Sep 11, 2021 at 05:30:45PM +0800, Huacai Chen wrote:
My original work is at [1].
Current default VGA device selection fails in some cases:
On BMC 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 on MIPS system, they are enumerated by pcibios_init(), which typically runs *after* vga_arb_device_init().
So I made vga_arb_update_default_device() to replace the current vga_ arb_select_default_device(), which will be 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. And the default VGA device is updated if a better one is found (device with legacy resources enabled is better, device owns the firmware framebuffer is even better).
Bjorn do some rework and extension in V2. It moves the VGA arbiter to the PCI subsystem, fixes a few nits, and breaks a few pieces to make the main patch a little smaller.
V3 rewrite the commit log of the last patch (which is also summarized by Bjorn).
V4 split the last patch to two steps.
V5 split big patches again and sort the patches.
Not sure if I'm missing something, or if this is an interim version and you're working on a v6.
From https://lore.kernel.org/r/20210909175926.GA996660@bjorn-Precision-5520, I was looking for:
BUT as I mentioned, I want the very first patch to be the very simple 2-line change to vga_arb_update_default_device() that actually fixes your problem.
That doesn't seem to be what we have here.
I try my best to split patches. But it seems very difficult to achieve the goal of "simple 2-line change" because I cannot break a single functional change. E.g., I think I can try to split Patch-5 again, but Patch-6 seems impossible.
Huacai
All comments welcome!
[1] https://lore.kernel.org/dri-devel/20210705100503.1120643-1-chenhuacai@loongs...
Bjorn Helgaas (4): PCI/VGA: Move vgaarb to drivers/pci PCI/VGA: Remove empty vga_arb_device_card_gone() PCI/VGA: Use unsigned format string to print lock counts PCI/VGA: Replace full MIT license text with SPDX identifier
Huacai Chen (7): PCI/VGA: Prefer vga_default_device() PCI/VGA: Move vga_arb_integrated_gpu() earlier in file PCI/VGA: Split out vga_arb_update_default_device() PCI/VGA: Update default VGA device if a better one found PCI/VGA: Update default VGA device again for X86/IA64 PCI/VGA: Remove vga_arb_select_default_device() PCI/VGA: Log bridge control messages when adding devices
Signed-off-by: Huacai Chen chenhuacai@loongson.cn Signed-off-by: Bjorn Helgaas bhelgaas@google.com
drivers/gpu/vga/Kconfig | 19 --- drivers/gpu/vga/Makefile | 1 - drivers/pci/Kconfig | 19 +++ drivers/pci/Makefile | 1 + drivers/{gpu/vga => pci}/vgaarb.c | 269 ++++++++++++------------------ 5 files changed, 126 insertions(+), 183 deletions(-) rename drivers/{gpu/vga => pci}/vgaarb.c (90%) -- 2.27.0