pc: add *bootscreen= variable to pass pre-initialized framebuffer info to kernel

EFI system has no cga or vesa anymore, so it becomes neccesary to
pass GOP framebuffer info to the kernel to get some output on the
screen.

sys/man/8/plan9.ini

@@ -831,6 +831,18 @@ If
 is set to
 .B ask
 then the user is prompted for a choice on boot.
+.SS \fL*bootscreen=\fIvalue\fP
+This is used by the kernel to attach a pre-initialized
+linear framebuffer that was setup by the bootloader
+or firmware.
+The
+.I value
+has four space separated fields: the resolution and bitdepth
+of the screen, the color channel descriptor, the physical
+address of the framebuffer and a optional aperture size.
+.EX
+	*bootscreen=800x600x32 x8r8g8b8 0x80000000 0x001d4c00
+.EE
 .SS \fL*dpms=\fIvalue\fP
 This is used to specify the screen blanking behavior of the MGA4xx
 video driver.

sys/src/9/pc/main.c

@@ -124,6 +124,7 @@ options(void)
 
 extern void mmuinit0(void);
 extern void (*i8237alloc)(void);
+extern void bootscreeninit(void);
 
 void
 main(void)
@@ -153,6 +154,7 @@ main(void)
 	printinit();
 	cpuidprint();
 	mmuinit();
+	bootscreeninit();
 	if(arch->intrinit)	/* launches other processors on an mp */
 		arch->intrinit();
 	timersinit();

sys/src/9/pc/screen.c

@@ -13,10 +13,6 @@
 #include <cursor.h>
 #include "screen.h"
 
-#define RGB2K(r,g,b)	((156763*(r)+307758*(g)+59769*(b))>>19)
-
-Point ZP = {0, 0};
-
 Rectangle physgscreenr;
 
 Memimage *gscreen;
@@ -531,7 +527,6 @@ vgalinearaddr(VGAscr *scr, ulong paddr, int size)
 	 * later, let's assume that we can just allocate the
 	 * entire window to start with.
 	 */
-
 	if(scr->paddr == paddr && size <= scr->apsize)
 		return;
 
@@ -542,7 +537,7 @@ vgalinearaddr(VGAscr *scr, ulong paddr, int size)
 		 */
 		error("cannot grow vga frame buffer");
 	}
-	
+
 	/* round to page boundary, just in case */
 	x = paddr&(BY2PG-1);
 	npaddr = paddr-x;
@@ -560,9 +555,104 @@ vgalinearaddr(VGAscr *scr, ulong paddr, int size)
 	scr->vaddr = (char*)scr->vaddr+x;
 	scr->paddr = paddr;
 	scr->apsize = nsize;
+
 	/* let mtrr harmlessly fail on old CPUs, e.g., P54C */
 	if(!waserror()){
 		mtrr(npaddr, nsize, "wc");
 		poperror();
 	}
 }
+
+/*
+ * called early on boot to attach to framebuffer
+ * setup by bootloader or firmware.
+ */
+void
+bootscreeninit(void)
+{
+	static Memdata md;
+	VGAscr *scr;
+	int x, y, z;
+	ulong chan, pa, sz;
+	char *s, *p;
+
+	/* *bootscreen=WIDTHxHEIGHTxDEPTH CHAN PA [SZ] */
+	s = getconf("*bootscreen");
+	if(s == nil)
+		return;
+
+	x = strtoul(s, &s, 0);
+	if(x == 0 || *s++ != 'x')
+		return;
+
+	y = strtoul(s, &s, 0);
+	if(y == 0 || *s++ != 'x')
+		return;
+
+	z = strtoul(s, &s, 0);
+	if(*s != ' ')
+		return;
+	if((p = strchr(++s, ' ')) == nil)
+		return;
+	*p = 0;
+	chan = strtochan(s);
+	*p = ' ';
+	if(chan == 0 || chantodepth(chan) != z)
+		return;
+
+	sz = 0;
+	pa = strtoul(p+1, &s, 0);
+	if(pa == 0)
+		return;
+	if(*s++ == ' ')
+		sz = strtoul(s, nil, 0);
+	if(sz < x * y * (z+7)/8)
+		sz = x * y * (z+7)/8;
+
+	/* round to pages */
+	z = pa&(BY2PG-1);
+	pa -= z;
+	sz += z;
+
+	/* map framebuffer */
+	scr = &vgascreen[0];
+	scr->apsize = PGROUND(sz);
+	scr->vaddr = vmap(pa, scr->apsize);
+	if(scr->vaddr == 0){
+		scr->apsize = 0;
+		return;
+	}
+	scr->vaddr = (char*)scr->vaddr + z;
+	scr->paddr = pa + z;
+
+	if(memimageinit() < 0)
+		return;
+
+	md.ref = 1;
+	md.bdata = scr->vaddr;
+	gscreen = allocmemimaged(Rect(0,0,x,y), chan, &md);
+	if(gscreen == nil)
+		return;
+
+	scr->palettedepth = 6;	/* default */
+	scr->memdefont = getmemdefont();
+	scr->gscreen = gscreen;
+	scr->gscreendata = gscreen->data;
+	scr->softscreen = 0;
+	scr->useflush = 0;
+	scr->dev = nil;
+
+	hwblank = 0;
+	hwaccel = 0;
+
+	physgscreenr = gscreen->r;
+
+	vgaimageinit(chan);
+	vgascreenwin(scr);
+
+	/* turn mouse cursor on */
+	swcursorinit();
+	scr->cur = &swcursor;
+	scr->cur->enable(scr);
+	cursoron();
+}