b1323e193a
Xorg on a framebuffer -- the fbdev video driver, the evdev input driver, libpciaccess -- asks the kernel a fixed set of questions before it draws anything, and gives up on the first wrong answer. These are those answers. evdev: EVIOCGVERSION, GID, GNAME, GPHYS, GUNIQ, GPROP, GBIT, GKEY, GABS, GREP and the accepted setters. Xorg and libinput decide what a device *is* from the capability bitmaps; /dev/input/eventN answered only EVIOCGRAB, which reads as no device at all. Each device's bitmaps are its defaults plus whatever it has reported, so a USB tablet makes the pointer absolute. fbdev: FBIOPUT_VSCREENINFO succeeds for the mode already set, as on Linux -- the fbdev driver sets it every time it starts -- and still refuses any other. FBIOPAN_DISPLAY to the origin; FBIOBLANK. The console: KDSETMODE(KD_GRAPHICS) stops it drawing on a terminal, KDSKBMODE(K_OFF) stops keys reaching its tty, and VT_PROCESS now does the switch handshake: leaving the terminal sends relsig and waits for VT_RELDISP, arriving sends acqsig. A terminal whose owner has died goes back to the kernel whole, so a crashed X cannot leave the console dead. /sys: boot_vga, a writable enable, and graphics/fb0 under the display device, which is how the fbdev driver pairs a card with /dev/fb0. ports/linux-headers: <linux/*.h> into musl's prefix, from sabotage- linux's kernel-headers 4.19.88-2. Its checksum is recorded from the first download; upstream publishes none. cmd/xready makes each call and checks the answer, including the switch handshake on tty2 and an owner that dies holding it. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
96 lines
3.7 KiB
C
96 lines
3.7 KiB
C
#pragma once
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// Framebuffer device ABI -- /dev/fb0.
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//
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// These are Linux's fbdev request numbers and structure layouts, not ours.
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// SchOS invented this device, so nothing forced the choice; matching Linux
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// was still the right one. A framebuffer is the first thing a graphics
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// program looks for, and every such program already knows how to ask
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// FBIOGET_VSCREENINFO. Inventing a private struct would have meant patching
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// each one we ever port, and -- worse -- a Linux-ABI binary calling
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// FBIOGET_VSCREENINFO would have gotten a *differently shaped* answer to a
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// request it thought it understood, which is the failure mode that made
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// `>>` truncate back when include/uapi/fcntl.h held xv6's open flags instead of
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// Linux's. Same lesson, applied before it bites rather than after.
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//
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// Plain C types throughout (no types.h) so userspace can include this
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// directly. Both sides are LP64.
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#define FBIOGET_VSCREENINFO 0x4600
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#define FBIOPUT_VSCREENINFO 0x4601
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#define FBIOGET_FSCREENINFO 0x4602
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#define FBIOBLANK 0x4611
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#define FBIOPAN_DISPLAY 0x4606
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// fb_fix_screeninfo.type
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#define FB_TYPE_PACKED_PIXELS 0
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// fb_fix_screeninfo.visual
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#define FB_VISUAL_TRUECOLOR 2
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// fb_var_screeninfo.activate
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#define FB_ACTIVATE_NOW 0
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// One colour channel's position within a pixel. `offset` is the bit position
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// of the channel's least significant bit; `length` is how many bits it gets.
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// A length of 0 means the channel does not exist -- which is how an opaque
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// framebuffer reports `transp`.
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struct fb_bitfield {
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unsigned int offset;
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unsigned int length;
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unsigned int msb_right; // != 0 means bit 0 is the MSB; never here
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};
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struct fb_var_screeninfo {
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unsigned int xres; // visible resolution
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unsigned int yres;
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unsigned int xres_virtual; // virtual resolution; == visible, no panning
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unsigned int yres_virtual;
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unsigned int xoffset; // offset of visible area within virtual
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unsigned int yoffset;
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unsigned int bits_per_pixel;
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unsigned int grayscale; // 0 == colour
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struct fb_bitfield red;
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struct fb_bitfield green;
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struct fb_bitfield blue;
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struct fb_bitfield transp;
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unsigned int nonstd; // 0 == standard pixel format
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unsigned int activate;
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unsigned int height; // physical size in mm; 0 == unknown, and
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unsigned int width; // VBE does not tell us, so it stays 0
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unsigned int accel_flags;
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// Timings. The mode is whatever the bootloader's VBE call established and
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// we cannot change it, so these are all reported as zero rather than
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// invented.
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unsigned int pixclock;
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unsigned int left_margin;
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unsigned int right_margin;
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unsigned int upper_margin;
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unsigned int lower_margin;
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unsigned int hsync_len;
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unsigned int vsync_len;
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unsigned int sync;
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unsigned int vmode;
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unsigned int rotate;
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unsigned int colorspace;
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unsigned int reserved[4];
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};
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struct fb_fix_screeninfo {
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char id[16]; // "schosfb"
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unsigned long smem_start; // physical address of the framebuffer
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unsigned int smem_len; // its length in bytes
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unsigned int type;
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unsigned int type_aux;
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unsigned int visual;
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unsigned short xpanstep; // 0 == panning unsupported
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unsigned short ypanstep;
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unsigned short ywrapstep;
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unsigned int line_length; // bytes per scanline (the VBE stride, which
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// is NOT always xres * bytes_per_pixel)
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unsigned long mmio_start; // no separate register aperture
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unsigned int mmio_len;
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unsigned int accel; // no acceleration
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unsigned short capabilities;
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unsigned short reserved[2];
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};
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