[PATCH v3 0/6] LoongArch: Identify the firmware/boot display device

[wuqianhai]

From: wuqianhai <wuqianhai@xxxxxxxxxxx>

On LoongArch the kernel cannot reliably identify the display device that
was set up by the firmware and used for the boot console.  Two code paths
need this information and currently get it wrong:

  * The PCI VGA arbiter: vga_is_firmware_default() is compiled only on
    x86, so on LoongArch vga_default_device() may select the wrong GPU
    when several are present (for example an integrated display
    controller and a discrete card).

  * The framebuffer console: LoongArch does not implement
    video_is_primary_device(), so with
    CONFIG_FRAMEBUFFER_CONSOLE_DETECT_PRIMARY=y the console falls back to
    the generic stub that always returns false and binds to the first
    registered framebuffer instead of the boot display.

This series fixes both by publishing the firmware framebuffer information
through screen_info on LoongArch and consuming it the same way x86 does.

Patch 1 always defines and initializes sysfb_primary_display, and always
provides its EFI stub alias, instead of guarding them behind
SYSFB/EFI_EARLYCON.

Patch 2 refreshes screen_info from the PCI resource-assignment path after
the root-bus resources are assigned, so the framebuffer address is final
before the VGA arbiter and sysfb_init() consume it.  The call is placed
in the LoongArch PCI scan path because only LoongArch has this ordering:
acpi_init() relocates the BAR before vga_arb_device_init() runs.  On x86
the screen_info address is still accurate at that point.  If you would
rather have the helper called from the generic
pci_assign_unassigned_root_bus_resources() path so that all architectures
share it, that can be done instead.

Patch 3 removes pci_fixup_vgadev(), which overrides the VGA default
device to a discrete card after the arbiter has already selected the
firmware framebuffer device, so vga_default_device() consistently
reflects the boot display.

Patch 4 implements video_is_primary_device() for LoongArch by reusing the
VGA default device selected by the arbiter.

Patch 5 lets the EFI stub link directly to sysfb_primary_display on
LoongArch, so the firmware framebuffer information is always populated.

Patch 6 lets the VGA arbiter use CONFIG_SCREEN_INFO instead of an
architecture check and makes VGA_ARB select SCREEN_INFO on LoongArch.

Patches 1-4 are LoongArch-specific.  Patches 5 and 6 touch generic code
(the EFI stub and the PCI VGA arbiter) and are placed last so they can be
reviewed and merged separately.  Patches 3 and 4 depend on patch 6 taking
effect, but are ordered ahead of it only to group the LoongArch changes
together.

Changes since v2:
  - Split the screen_info refresh out of vga_arb_device_init() into the
    LoongArch PCI resource-assignment path (patch 2), following Thomas'
    suggestion to decouple it from sysfb_init().
  - Drop the per-architecture check in vgaarb.c and the select of SYSFB
    in favour of CONFIG_SCREEN_INFO and select SCREEN_INFO (patch 6).
  - Always define and initialize sysfb_primary_display, and let the EFI
    stub link to it directly (patches 1 and 5), instead of guarding them
    behind SYSFB/EFI_EARLYCON.
  - Remove the vga_default_device() override (patch 3) so the arbiter's
    firmware-framebuffer selection takes effect.
  - Implement video_is_primary_device() (patch 4) by reusing the arbiter's
    default device, so FRAMEBUFFER_CONSOLE_DETECT_PRIMARY works.

Build-tested on loongarch64 with GCC 8.3.0.

wuqianhai (6):
  LoongArch: efi: Provide sysfb_primary_display for screen_info users
  LoongArch/PCI: Refresh screen_info after resource assignment
  LoongArch/PCI: Remove vga default device override
  LoongArch: video: Implement primary framebuffer device detection
  efi/libstub: Enable direct sysfb_primary_display access on LoongArch
  PCI/VGA: Enable firmware default device detection on LoongArch

 arch/loongarch/Makefile                       |  3 ++
 arch/loongarch/include/asm/video.h            |  7 +++++
 arch/loongarch/kernel/efi.c                   |  5 +---
 arch/loongarch/kernel/image-vars.h            |  2 --
 arch/loongarch/pci/acpi.c                     |  4 +++
 arch/loongarch/pci/pci.c                      | 18 ------------
 arch/loongarch/video/Makefile                 |  3 ++
 arch/loongarch/video/video-common.c           | 29 +++++++++++++++++++
 drivers/firmware/efi/libstub/efi-stub-entry.c |  1 +
 drivers/pci/Kconfig                           |  2 +-
 drivers/pci/vgaarb.c                          |  2 +-
 11 files changed, 50 insertions(+), 26 deletions(-)
 create mode 100644 arch/loongarch/video/Makefile
 create mode 100644 arch/loongarch/video/video-common.c

-- 
2.34.1