daniel/MontaukOS
1
Fork 0
Code Issues 3 Pull Requests Actions Packages Projects Releases Wiki Activity

feat: vblank IRQ and double-buffered page flip for Intel GPU

Browse Source 
Add tear-free scanout to the Intel GPU driver: a second kernel-allocated
scanout buffer, DSPASURF flips latched at vblank, and a vblank interrupt
delivered over MSI (Gen 11+ master/display/pipe IRQ chain) with a
monotonic vblank counter and WaitVblank().

Expose it as SYS_FBFLIP (150): index selects the front buffer, -1
queries support, flags bit0 waits for the flip to latch. fb_map() now
maps buffer 1 right after buffer 0 when flipping is available, and
gui::Framebuffer draws to the off-screen buffer and flips with vsync,
falling back to the direct copy when unsupported.

Scanout is restored to buffer 0 when the flip-owning process exits and
on panic, so the terminal and panic box never land on the invisible
buffer.

Co-Authored-By: Claude Fable 5 <[email protected]>
This commit is contained in:
daniel
2026-07-13 21:53:06 +02:00
co-authored by Claude Fable 5
parent 500020ce47
commit 182520a585
14 changed files with 549 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files
programs/include/gui/framebuffer.hpp
+27 -2
View File
@@ -14,10 +14,12 @@ namespace gui {
class Framebuffer {
uint32_t* hw_fb;
uint32_t* hw_fb2; // second scanout buffer (page flip), nullptr if unsupported
uint32_t* back_buf;
int fb_width;
int fb_height;
int fb_pitch; // in bytes
int hw_next; // scanout buffer the next flip() will present (page flip only)
static inline void fill_pixels(uint32_t* dst, int count, uint32_t pixel) {
if (!dst || count <= 0) return;
@@ -60,7 +62,8 @@ class Framebuffer {
}
public:
Framebuffer() : hw_fb(nullptr), back_buf(nullptr), fb_width(0), fb_height(0), fb_pitch(0) {
Framebuffer() : hw_fb(nullptr), hw_fb2(nullptr), back_buf(nullptr),
fb_width(0), fb_height(0), fb_pitch(0), hw_next(1) {
montauk::abi::FbInfo info;
montauk::fb_info(&info);
@@ -70,6 +73,13 @@ public:
hw_fb = (uint32_t*)montauk::fb_map();
back_buf = (uint32_t*)montauk::alloc((uint64_t)fb_height * fb_pitch);
// Hardware page flipping: fb_map() maps the second scanout buffer
// directly after the first when the kernel supports flipping.
if (hw_fb && montauk::fb_flip(-1, 0) == 1) {
uint64_t pages = ((uint64_t)fb_height * fb_pitch + 0xFFF) / 0x1000;
hw_fb2 = (uint32_t*)((uint8_t*)hw_fb + pages * 0x1000);
}
}
int width() const { return fb_width; }
@@ -250,13 +260,28 @@ public:
inline void flip() {
if (!hw_fb || !back_buf) return;
// With hardware page flipping, copy into the scanout buffer that is
// currently OFF screen, then ask the display engine to present it at
// the next vblank (tear-free). Without it, fall back to copying
// straight into the visible framebuffer.
uint32_t* dst_fb = hw_fb;
if (hw_fb2) dst_fb = (hw_next == 1) ? hw_fb2 : hw_fb;
// Copy back buffer to hardware framebuffer, row by row (pitch may differ)
uint64_t row_bytes = (uint64_t)fb_width * sizeof(uint32_t);
for (int y = 0; y < fb_height; y++) {
uint32_t* src = (uint32_t*)((uint8_t*)back_buf + y * fb_pitch);
uint32_t* dst = (uint32_t*)((uint8_t*)hw_fb + y * fb_pitch);
uint32_t* dst = (uint32_t*)((uint8_t*)dst_fb + y * fb_pitch);
montauk::memcpy(dst, src, row_bytes);
}
if (hw_fb2) {
// Wait for the latch (vsync): the buffer we just left becomes
// safe to draw into only once the new one is actually scanning.
if (montauk::fb_flip(hw_next, 1) == hw_next) {
hw_next ^= 1;
}
}
}
};