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SubjectRe: [Linux-fbdev-devel] [RFC][PATCH][FBDEV]: Setting fbcon's windows size
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Hi James, 

Here's an improved GTF implementation. I was a bit delayed because I
was trying to find a way to do square roots without using floating
point. The diff is against linux-2.5.54 + your latest fbdev.diff.

static int fb_get_mode(int flags, u32 val, struct fb_var_screeninfo
*var, struct fb_info *info);

if flags == 0: maximize timings
1: vrefresh rate driven calculation
2. hscan rate driven calculation
3. pixelclock driven calculation.

The parameter 'val' depends on the parameter 'flags': ignored if flags
== 0, in Hz if 1 and 2, in picoseconds if 3.

The flags are useful for cases such as a fixed-frequency monitor (pass
flags = 2) or for hardware which only have several sets of dotclocks to
use. In this case, it will run the GTF first, get the resulting
pixelclock to select a dotclock from the driver's own set, then rerun
the GTF using flags=3, and val = selected dotclock.

Probably still has precision errors, like converting KHZ to picoseconds,
but is more or less usable. Tested with i810fb and rivafb. (For rivafb,
I have to use a hacked version. The latest one does not work for the
riva128).

BTW, I downloaded the source code of read-edid, and it seems that the
following monitor limits are parsable from the EDID block: HorizSync,
VertRefresh, DotClock, and GTF capability. We may change info->monspecs
to match that. Also, the EDID contains a list of supported modes, but
there's only 4 of them(?).

Tony

diff -Naur linux-2.5.54/drivers/video/fbmon.c linux/drivers/video/fbmon.c
--- linux-2.5.54/drivers/video/fbmon.c 2003-01-08 04:19:48.000000000 +0000
+++ linux/drivers/video/fbmon.c 2003-01-08 04:18:11.000000000 +0000
@@ -289,7 +289,376 @@
}
#endif

+/*
+ * VESA Generalized Timing Formula (GTF)
+ */
+
+#define FLYBACK 550
+#define V_FRONTPORCH 1
+#define H_OFFSET 40
+#define H_SCALEFACTOR 20
+#define H_BLANKSCALE 128
+#define H_GRADIENT 600
+#define C_VAL 30
+#define M_VAL 300
+
+struct __fb_timings {
+ u32 dclk;
+ u32 hfreq;
+ u32 vfreq;
+ u32 hactive;
+ u32 vactive;
+ u32 hblank;
+ u32 vblank;
+ u32 htotal;
+ u32 vtotal;
+};
+
+/*
+ * a simple function to get the square root of integers
+ */
+static u32 fb_sqrt(int x)
+{
+ register int op, res, one;
+
+ op = x;
+ res = 0;
+
+ one = 1 << 30;
+ while (one > op) one >>= 2;
+
+ while (one != 0) {
+ if (op >= res + one) {
+ op = op - (res + one);
+ res = res + 2 * one;
+ }
+ res /= 2;
+ one /= 4;
+ }
+ return((u32) res);
+}
+
+/**
+ * fb_get_vblank - get vertical blank time
+ * @hfreq: horizontal freq
+ *
+ * DESCRIPTION:
+ * vblank = right_margin + vsync_len + left_margin
+ *
+ * given: right_margin = 1 (V_FRONTPORCH)
+ * vsync_len = 3
+ * flyback = 550
+ *
+ * flyback * hfreq
+ * left_margin = --------------- - vsync_len
+ * 1000000
+ */
+static u32 fb_get_vblank(u32 hfreq)
+{
+ u32 vblank;
+
+ vblank = (hfreq * FLYBACK)/1000;
+ vblank = (vblank + 500)/1000;
+ return (vblank + V_FRONTPORCH);
+}
+
+/**
+ * fb_get_hblank_by_freq - get horizontal blank time given hfreq
+ * @hfreq: horizontal freq
+ * @xres: horizontal resolution in pixels
+ *
+ * DESCRIPTION:
+ *
+ * xres * duty_cycle
+ * hblank = ------------------
+ * 100 - duty_cycle
+ *
+ * duty cycle = percent of htotal assigned to inactive display
+ * duty cycle = C - (M/Hfreq)
+ *
+ * where: C = ((offset - scale factor) * blank_scale)
+ * -------------------------------------- + scale factor
+ * 256
+ * M = blank_scale * gradient
+ *
+ */
+static u32 fb_get_hblank_by_hfreq(u32 hfreq, u32 xres)
+{
+ u32 c_val, m_val, duty_cycle, hblank;
+
+ c_val = (((H_OFFSET - H_SCALEFACTOR) * H_BLANKSCALE)/256 +
+ H_SCALEFACTOR) * 1000;
+ m_val = (H_BLANKSCALE * H_GRADIENT)/256;
+ m_val = (m_val * 1000000)/hfreq;
+ duty_cycle = c_val - m_val;
+ hblank = (xres * duty_cycle)/(100000 - duty_cycle);
+ return (hblank);
+}
+
+/**
+ * fb_get_hblank_by_dclk - get horizontal blank time given pixelclock
+ * @dclk: pixelclock in Hz
+ * @xres: horizontal resolution in pixels
+ *
+ * DESCRIPTION:
+ *
+ * xres * duty_cycle
+ * hblank = ------------------
+ * 100 - duty_cycle
+ *
+ * duty cycle = percent of htotal assigned to inactive display
+ * duty cycle = C - (M * h_period)
+ *
+ * where: h_period = SQRT(100 - C + (0.4 * xres * M)/dclk) + C - 100
+ * -----------------------------------------------
+ * 2 * M
+ * M = 300;
+ * C = 30;
+
+ */
+static u32 fb_get_hblank_by_dclk(u32 dclk, u32 xres)
+{
+ u32 duty_cycle, h_period, hblank;;
+
+ dclk /= 1000;
+ h_period = 100 - C_VAL;
+ h_period *= h_period;
+ h_period += (M_VAL * xres * 2 * 1000)/(5 * dclk);
+ h_period *=10000;
+
+ h_period = fb_sqrt((int) h_period);
+ h_period -= (100 - C_VAL) * 100;
+ h_period *= 1000;
+ h_period /= 2 * M_VAL;
+
+ duty_cycle = C_VAL * 1000 - (M_VAL * h_period)/100;
+ hblank = (xres * duty_cycle)/(100000 - duty_cycle) + 8;
+ hblank &= ~15;
+ return (hblank);
+}
+
+/**
+ * fb_get_hfreq - estimate hsync
+ * @vfreq: vertical refresh rate
+ * @yres: vertical resolution
+ *
+ * DESCRIPTION:
+ *
+ * (yres + front_port) * vfreq * 1000000
+ * hfreq = -------------------------------------
+ * (1000000 - (vfreq * FLYBACK)
+ *
+ */
+
+static u32 fb_get_hfreq(u32 vfreq, u32 yres)
+{
+ u32 divisor, hfreq;
+
+ divisor = (1000000 - (vfreq * FLYBACK))/1000;
+ hfreq = (yres + V_FRONTPORCH) * vfreq * 1000;
+ return (hfreq/divisor);
+}
+
+static void fb_timings_vfreq(struct __fb_timings *timings)
+{
+ timings->hfreq = fb_get_hfreq(timings->vfreq, timings->vactive);
+ timings->vblank = fb_get_vblank(timings->hfreq);
+ timings->vtotal = timings->vactive + timings->vblank;
+ timings->hblank = fb_get_hblank_by_hfreq(timings->hfreq,
+ timings->hactive);
+ timings->htotal = timings->hactive + timings->hblank;
+ timings->dclk = timings->htotal * timings->hfreq;
+}
+
+static void fb_timings_hfreq(struct __fb_timings *timings)
+{
+ timings->vblank = fb_get_vblank(timings->hfreq);
+ timings->vtotal = timings->vactive + timings->vblank;
+ timings->vfreq = timings->hfreq/timings->vtotal;
+ timings->hblank = fb_get_hblank_by_hfreq(timings->hfreq,
+ timings->hactive);
+ timings->htotal = timings->hactive + timings->hblank;
+ timings->dclk = timings->htotal * timings->hfreq;
+}
+
+static void fb_timings_dclk(struct __fb_timings *timings)
+{
+ timings->hblank = fb_get_hblank_by_dclk(timings->dclk,
+ timings->hactive);
+ timings->htotal = timings->hactive + timings->hblank;
+ timings->hfreq = timings->dclk/timings->htotal;
+ timings->vblank = fb_get_vblank(timings->hfreq);
+ timings->vtotal = timings->vactive + timings->vblank;
+ timings->vfreq = timings->hfreq/timings->vtotal;
+}
+
+/*
+ * fb_get_mode - calculates video mode using VESA GTF
+ * @flags: if: 0 - maximize vertical refresh rate
+ * 1 - vrefresh-driven calculation;
+ * 2 - hscan-driven calculation;
+ * 3 - pixelclock-driven calculation;
+ * @val: depending on @flags, ignored, vrefresh, hsync or pixelclock
+ * @var: pointer to fb_var_screeninfo
+ * @info: pointer to fb_info
+ *
+ * DESCRIPTION:
+ * Calculates video mode based on monitor specs using VESA GTF.
+ * The GTF is best for VESA GTF compliant monitors but is
+ * specifically formulated to work for older monitors as well.
+ *
+ * If @flag==0, the function will attempt to maximize the
+ * refresh rate. Otherwise, it will calculate timings based on
+ * the flag and accompanying value.
+ *
+ * All calculations are based on the VESA GTF Spreadsheet
+ * available at VESA's public ftp (http://www.vesa.org).
+ *
+ * NOTES:
+ * The timings generated by the GTF will be different from VESA
+ * DMT. It might be a good idea to keep a table of standard
+ * VESA modes as well. The GTF may also not work for some displays,
+ * such as, and especially, analog TV.
+ *
+ * REQUIRES:
+ * A valid info->monspecs, otherwise 'safe numbers' will be used.
+ */
+int fb_get_mode(int flags, u32 val, struct fb_var_screeninfo *var, struct fb_info *info)
+{
+ struct __fb_timings timings;
+ u32 interlace = 1, dscan = 1;
+ u32 hfmin, hfmax, vfmin, vfmax;
+
+ /*
+ * If monspecs are invalid, use values that are enough
+ * for 640x480@60
+ */
+ if ((!info->monspecs.hfmax && !info->monspecs.vfmax) ||
+ info->monspecs.hfmax < info->monspecs.hfmin ||
+ info->monspecs.vfmax < info->monspecs.vfmin) {
+ hfmin = 29000; hfmax = 30000;
+ vfmin = 60; vfmax = 60;
+ } else {
+ hfmin = info->monspecs.hfmin;
+ hfmax = info->monspecs.hfmax;
+ vfmin = info->monspecs.vfmin;
+ vfmax = info->monspecs.vfmax;
+ }
+
+ memset(&timings, 0, sizeof(struct __fb_timings));
+ timings.hactive = var->xres;
+ timings.vactive = var->yres;
+ if (var->vmode & FB_VMODE_INTERLACED) {
+ timings.vactive /= 2;
+ interlace = 2;
+ }
+ if (var->vmode & FB_VMODE_DOUBLE) {
+ timings.vactive *= 2;
+ dscan = 2;
+ }
+
+ switch (flags) {
+ case 0: /* maximize refresh rate */
+ timings.hfreq = hfmax;
+ fb_timings_hfreq(&timings);
+ if (timings.vfreq > vfmax) {
+ timings.vfreq = vfmax;
+ fb_timings_vfreq(&timings);
+ }
+ break;
+ case 1: /* vrefresh driven */
+ timings.vfreq = val;
+ fb_timings_vfreq(&timings);
+ break;
+ case 2: /* hsync driven */
+ timings.hfreq = val;
+ fb_timings_hfreq(&timings);
+ break;
+ case 3: /* pixelclock driven */
+ timings.dclk = PICOS2KHZ(val) * 1000;
+ fb_timings_dclk(&timings);
+ break;
+ default:
+ return -EINVAL;
+
+ }
+
+ if (timings.vfreq < vfmin || timings.vfreq > vfmax ||
+ timings.hfreq < hfmin || timings.hfreq > hfmax)
+ return -EINVAL;
+
+
+ var->pixclock = KHZ2PICOS(timings.dclk/1000);
+ var->hsync_len = (timings.htotal * 8)/100;
+ var->right_margin = (timings.hblank/2) - var->hsync_len;
+ var->left_margin = timings.hblank - var->right_margin - var->hsync_len;
+
+ var->vsync_len = (3 * interlace)/dscan;
+ var->lower_margin = (1 * interlace)/dscan;
+ var->upper_margin = (timings.vblank * interlace)/dscan -
+ (var->vsync_len + var->lower_margin);
+
+ return 0;
+}
+
+/*
+ * fb_validate_mode - validates var against monitor capabilities
+ * @var: pointer to fb_var_screeninfo
+ * @info: pointer to fb_info
+ *
+ * DESCRIPTION:
+ * Validates video mode against monitor capabilities specified in
+ * info->monspecs.
+ *
+ * REQUIRES:
+ * A valid info->monspecs.
+ */
+int fb_validate_mode(struct fb_var_screeninfo *var, struct fb_info *info)
+{
+ u32 hfreq, vfreq, htotal, vtotal, pixclock;
+ u32 hfmin, hfmax, vfmin, vfmax;
+
+ /*
+ * If monspecs are invalid, use values that are enough
+ * for 640x480@60
+ */
+ if ((!info->monspecs.hfmax && !info->monspecs.vfmax) ||
+ info->monspecs.hfmax < info->monspecs.hfmin ||
+ info->monspecs.vfmax < info->monspecs.vfmin) {
+ hfmin = 29000; hfmax = 30000;
+ vfmin = 60; vfmax = 60;
+ } else {
+ hfmin = info->monspecs.hfmin;
+ hfmax = info->monspecs.hfmax;
+ vfmin = info->monspecs.vfmin;
+ vfmax = info->monspecs.vfmax;
+ }
+
+ if (!var->pixclock)
+ return -EINVAL;
+ pixclock = PICOS2KHZ(var->pixclock) * 1000;
+
+ htotal = var->xres + var->right_margin + var->hsync_len +
+ var->left_margin;
+ vtotal = var->yres + var->lower_margin + var->vsync_len +
+ var->upper_margin;
+
+ if (var->vmode & FB_VMODE_INTERLACED)
+ vtotal /= 2;
+ if (var->vmode & FB_VMODE_DOUBLE)
+ vtotal *= 2;
+
+ hfreq = pixclock/htotal;
+ vfreq = hfreq/vtotal;
+
+ return (vfreq < vfmin || vfreq > vfmax ||
+ hfreq < hfmin || hfreq > hfmax) ?
+ -EINVAL : 0;
+}
+
EXPORT_SYMBOL(parse_edid);
#ifdef CONFIG_PCI
EXPORT_SYMBOL(get_EDID);
#endif
+EXPORT_SYMBOL(fb_get_mode);
+EXPORT_SYMBOL(fb_validate_mode);
diff -Naur linux-2.5.54/include/linux/fb.h linux/include/linux/fb.h
--- linux-2.5.54/include/linux/fb.h 2003-01-08 04:20:07.000000000 +0000
+++ linux/include/linux/fb.h 2003-01-08 04:19:26.000000000 +0000
@@ -468,6 +468,10 @@
extern int fbmon_valid_timings(u_int pixclock, u_int htotal, u_int vtotal,
const struct fb_info *fb_info);
extern int fbmon_dpms(const struct fb_info *fb_info);
+extern int fb_get_mode(int flags, u32 val, struct fb_var_screeninfo *var,
+ struct fb_info *info);
+extern int fb_validate_mode(struct fb_var_screeninfo *var,
+ struct fb_info *info);

/* drivers/video/fbcmap.c */
extern int fb_alloc_cmap(struct fb_cmap *cmap, int len, int transp);
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