Same disease as the network stack, one subsystem over. kernel/dev/vga.c
was three things wearing one name: the owner of the framebuffer, a
bitmap drawing library, and the text console. Only the first is a
driver, and because they shared a file they shared a prefix -- so
panic.c drew the crash screen with vga_fill_rect, console.c printed with
vga_putc, /dev/fb0 handed out vga_fb_phys, and every one of those files
named a display driver it had no business knowing about.
Split three ways:
- kernel/drivers/gpu/vga/vga_fb.c owns the VBE framebuffer -- the mode
the loader programmed and handed over, the aperture, and the display
class vtable. It is a driver and now lives with the driver that
finds the card on the bus.
- kernel/dev/gfx.c draws: pixels, shapes, glyphs, the cursor, scroll,
the ANSI erase operations. It names no driver. The framebuffer
arrives through gfx_attach_scanout(), so a driver publishes what it
owns and this file draws on it without knowing what it is.
- include/gfx.h is the interface, and says why it is deliberately not
the display class: that one is about frames -- acquire, present,
vblank -- and the crash screen has to work when nothing else does.
main() no longer calls a display driver. platform_register_devices()
takes the framebuffer address and brings up whatever owns it, which is
where driver names belong; kernel/drivers/registry.c is the file whose
entire job is naming every driver in the kernel.
virtio-gpu got the e1000 treatment as well: instances in an array, the
instance hung on dev->priv by an `attached` hook, and every op reading
it rather than a file-static. It refused the second adapter outright
before, which is not hypothetical -- integrated plus discrete is an
ordinary laptop. The VGA driver deliberately has no such hook, and says
so: there is one framebuffer the loader programmed however many
VGA-class controllers the bus turns up, and a second one publishing the
same scanout is the truth rather than a bug.
Private headers moved next to their drivers: include/virtio.h and
include/xhci.h each had exactly one includer. include/ is for headers
the rest of the kernel needs.
Deleted rather than moved: consoleinit() programmed the sixteen ANSI
colours into the VGA DAC and disabled text-mode blink, by writing ports
0x3C0-0x3C9 from the console. The comment three lines above the colour
table already said this does nothing in a 32bpp linear mode -- there is
no palette to index -- so it was both dead and in the wrong file.
Verified, and this is a refactor so the evidence is that nothing moved:
- bootcheck -Fb -Net: 59 [ok], no failures. That covers the console
through every command, /dev/fb0's geometry, writing pixels through
write() and mapping the framebuffer through mmap.
- make crashshot: the crash screen renders exactly as before --
shapes, glyphs, logo and QR code -- which is the whole of gfx.c
exercised at once, in a panic, with the scanout attached by a driver.
- make schcom-test: five pixel assertions from the host oracle still
pass, so the display class and the compositor above it are unmoved.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Every driver reached its registers with P2V(bar.base), which assumes the
BAR sits inside the 0-4 GB the direct map covers. Under SeaBIOS it always
does. Under OVMF it does not: firmware may place a 64-bit BAR anywhere,
and it puts virtio-gpu's at about 768 GB. P2V produced an address with no
translation behind it, so the driver's first register write took a page
fault, then a double fault, then a triple fault and a reboot loop --
which, coming from a driver bind, reads as broken hardware rather than a
missing mapping.
ioremap() carries each region on a 1 GB page in PDPT entries 4-511, which
were unused: the direct map occupies 0-3, and kpml4[0], kpml4[KERNBASE]
and every process's PML4 all share that one table, so a mapping appears
in every address space at once with no page table to allocate. The pages
are cache-disabled and write-through for the same reason the top GB of
the direct map is -- these are registers, and a write sitting in a cache
line is a write the device never sees.
A physical address below 4 GB returns the direct-map address unchanged,
so the BIOS path, where every BAR is low, is byte for byte what it was.
virtio-gpu now initialises under OVMF (1280x800, queue 64) instead of
triple faulting. e1000 and xhci had the identical latent bug; xhci was
already refusing to bind above 4 GB with a comment saying the mapping did
not exist yet, and now it does.
BIOS unchanged: bootcheck 108 [ok] with -Fb -Tty -Usb -Sock -Evdev -Ps,
e1000 and xhci both binding.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
An x86-64 operating system built from xv6, now largely rewritten: SMP,
a copy-on-write root filesystem (SchFS), PCI/USB/virtio drivers, a TTF
rasteriser, and a Linux-numbered syscall ABI.
No history before this point -- the tree was never under version control.
This commit exists so the rename that follows has something to undo to.
