Introduce di_gtf_compute()

This is a function to compute a timing according to GTF.

Signed-off-by: Simon Ser <contact@emersion.fr>

di-edid-decode.c

@@ -6,9 +6,10 @@
 #include <getopt.h>
 
 #include <libdisplay-info/cta.h>
+#include <libdisplay-info/displayid.h>
 #include <libdisplay-info/dmt.h>
 #include <libdisplay-info/edid.h>
-#include <libdisplay-info/displayid.h>
+#include <libdisplay-info/gtf.h>
 #include <libdisplay-info/info.h>
 
 static struct {
@@ -57,11 +58,14 @@ print_standard_timing(const struct di_edid_standard_timing *t)
 	int32_t vert_video;
 	const struct di_dmt_timing *dmt;
 	int hbl, vbl, horiz_total, vert_total;
-	double refresh, horiz_freq_hz, pixel_clock_mhz;
+	double refresh, horiz_freq_hz, pixel_clock_mhz, pixel_clock_khz;
+	struct di_gtf_options gtf_options;
+	struct di_gtf_timing gtf;
 
 	vert_video = di_edid_standard_timing_get_vert_video(t);
 	dmt = di_edid_standard_timing_get_dmt(t);
 
+	printf("    ");
 	if (dmt) {
 		hbl = dmt->horiz_blank - 2 * dmt->horiz_border;
 		vbl = dmt->vert_blank - 2 * dmt->vert_border;
@@ -70,15 +74,37 @@ print_standard_timing(const struct di_edid_standard_timing *t)
 		refresh = (double) dmt->pixel_clock_hz / (horiz_total * vert_total);
 		horiz_freq_hz = (double) dmt->pixel_clock_hz / horiz_total;
 		pixel_clock_mhz = (double) dmt->pixel_clock_hz / (1000 * 1000);
+
+		printf("DMT 0x%02x", dmt ? dmt->dmt_id : 0);
 	} else {
-		/* TODO: GTF and CVT timings */
+		/* TODO: CVT timings */
-		refresh = 0;
+
-		horiz_freq_hz = 0;
+		gtf_options = (struct di_gtf_options) {
-		pixel_clock_mhz = 0;
+			.h_pixels = t->horiz_video,
+			.v_lines = vert_video,
+			.ip_param = DI_GTF_IP_PARAM_V_FRAME_RATE,
+			.ip_freq_rqd = t->refresh_rate_hz,
+			.m = DI_GTF_DEFAULT_M,
+			.c = DI_GTF_DEFAULT_C,
+			.k = DI_GTF_DEFAULT_K,
+			.j = DI_GTF_DEFAULT_J,
+		};
+		di_gtf_compute(&gtf, &gtf_options);
+
+		hbl = gtf.h_front_porch + gtf.h_sync + gtf.h_back_porch + 2 * gtf.h_border;
+		vbl = gtf.v_front_porch + gtf.v_sync + gtf.v_back_porch + 2 * gtf.v_border;
+		horiz_total = gtf.h_pixels + hbl;
+		vert_total = gtf.v_lines + vbl;
+		/* Upstream edid-decode rounds the pixel clock to kHz... */
+		pixel_clock_khz = round(gtf.pixel_freq_mhz * 1000);
+		refresh = (pixel_clock_khz * 1000) / (horiz_total * vert_total);
+		horiz_freq_hz = (pixel_clock_khz * 1000) / horiz_total;
+		pixel_clock_mhz = pixel_clock_khz / 1000;
+
+		printf("GTF     ");
 	}
 
-	printf("    ");
+	printf(":");
-	printf("DMT 0x%02x:", dmt ? dmt->dmt_id : 0);
 	printf(" %5dx%-5d", t->horiz_video, vert_video);
 	printf(" %10.6f Hz", refresh);
 	printf("  %s ", standard_timing_aspect_ratio_name(t->aspect_ratio));

gtf.c

@@ -0,0 +1,129 @@
+/*
+ * Copyright 2006-2012 Red Hat, Inc.
+ * Copyright 2018-2021 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
+ *
+ * Originally imported from edid-decode.
+ */
+
+#include <math.h>
+
+#include <libdisplay-info/gtf.h>
+
+/**
+ * The assumed character cell granularity of the graphics system, in pixels.
+ */
+#define CELL_GRAN 8.0
+/**
+ * The size of the top and bottom overscan margin as a percentage of the active
+ * vertical image.
+ */
+#define MARGIN_PERC 1.8
+/**
+ * The minimum front porch in lines (vertical) and character cells (horizontal).
+ */
+#define MIN_PORCH 1.0
+/**
+ * The width of the V sync in lines.
+ */
+#define V_SYNC_RQD 3.0
+/**
+ * The width of the H sync as a percentage of the total line period.
+ */
+#define H_SYNC_PERC 8.0
+/**
+ * Minimum time of vertical sync + back porch interval (µs).
+ */
+#define MIN_VSYNC_BP 550.0
+
+void di_gtf_compute(struct di_gtf_timing *t, const struct di_gtf_options *options)
+{
+	double c_prime, m_prime, h_pixels_rnd, v_lines_rnd, h_margin,
+	       v_margin, interlace, total_active_pixels, pixel_freq,
+	       h_blank_pixels, total_pixels, v_sync_bp, v_field_rate_rqd,
+	       h_period_est, total_v_lines, v_field_rate_est, h_period,
+	       ideal_duty_cycle, h_freq, ideal_h_period, v_back_porch, h_sync,
+	       h_front_porch;
+
+	/* C' and M' are part of the Blanking Duty Cycle computation */
+	c_prime = ((options->c - options->j) * options->k / 256.0) + options->j;
+	m_prime = options->k / 256.0 * options->m;
+
+	h_pixels_rnd = round(options->h_pixels / CELL_GRAN) * CELL_GRAN;
+	v_lines_rnd = options->int_rqd ?
+		      round(options->v_lines / 2.0) :
+		      options->v_lines;
+	h_margin = options->margins_rqd ?
+		   round(h_pixels_rnd * MARGIN_PERC / 100.0 / CELL_GRAN) * CELL_GRAN :
+		   0;
+	v_margin = options->margins_rqd ?
+		   round(MARGIN_PERC / 100.0 * v_lines_rnd) :
+		   0;
+	interlace = options->int_rqd ? 0.5 : 0;
+	total_active_pixels = h_pixels_rnd + h_margin * 2;
+
+	switch (options->ip_param) {
+	case DI_GTF_IP_PARAM_V_FRAME_RATE:
+		// vertical frame frequency (Hz)
+		v_field_rate_rqd = options->int_rqd ?
+				   options->ip_freq_rqd * 2 :
+				   options->ip_freq_rqd;
+		h_period_est = (1.0 / v_field_rate_rqd - MIN_VSYNC_BP / 1000000.0) /
+			       (v_lines_rnd + v_margin * 2 + MIN_PORCH + interlace) * 1000000.0;
+		v_sync_bp = round(MIN_VSYNC_BP / h_period_est);
+		total_v_lines = v_lines_rnd + v_margin * 2 +
+				v_sync_bp + interlace + MIN_PORCH;
+		v_field_rate_est = 1.0 / h_period_est / total_v_lines * 1000000.0;
+		h_period = h_period_est / (v_field_rate_rqd / v_field_rate_est);
+		ideal_duty_cycle = c_prime - m_prime * h_period / 1000.0;
+		h_blank_pixels = round(total_active_pixels * ideal_duty_cycle /
+				       (100.0 - ideal_duty_cycle) /
+				       (2 * CELL_GRAN)) * 2 * CELL_GRAN;
+		total_pixels = total_active_pixels + h_blank_pixels;
+		pixel_freq = total_pixels / h_period;
+		break;
+	case DI_GTF_IP_PARAM_H_FREQ:
+		// horizontal frequency (kHz)
+		h_freq = options->ip_freq_rqd;
+		v_sync_bp = round(MIN_VSYNC_BP * h_freq / 1000.0);
+		ideal_duty_cycle = c_prime - m_prime / h_freq;
+		h_blank_pixels = round(total_active_pixels * ideal_duty_cycle /
+				       (100.0 - ideal_duty_cycle) /
+				       (2 * CELL_GRAN)) * 2 * CELL_GRAN;
+		total_pixels = total_active_pixels + h_blank_pixels;
+		pixel_freq = total_pixels * h_freq / 1000.0;
+		break;
+	case DI_GTF_IP_PARAM_H_PIXELS:
+		// pixel clock rate (MHz)
+		pixel_freq = options->ip_freq_rqd;
+		ideal_h_period = (c_prime - 100.0 +
+				  sqrt((100.0 - c_prime) * (100.0 - c_prime) +
+				       0.4 * m_prime * (total_active_pixels + h_margin * 2) / pixel_freq))
+				  / 2.0 / m_prime * 1000.0;
+		ideal_duty_cycle = c_prime - m_prime * ideal_h_period / 1000.0;
+		h_blank_pixels = round(total_active_pixels * ideal_duty_cycle /
+				       (100.0 - ideal_duty_cycle) /
+				       (2 * CELL_GRAN)) * 2 * CELL_GRAN;
+		total_pixels = total_active_pixels + h_blank_pixels;
+		h_freq = pixel_freq / total_pixels * 1000.0;
+		v_sync_bp = round(MIN_VSYNC_BP * h_freq / 1000.0);
+		break;
+	}
+
+	v_back_porch = v_sync_bp - V_SYNC_RQD;
+	h_sync = round(H_SYNC_PERC / 100.0 * total_pixels / CELL_GRAN) * CELL_GRAN;
+	h_front_porch = h_blank_pixels / 2.0 - h_sync;
+
+	*t = (struct di_gtf_timing) {
+		.h_pixels = (int) h_pixels_rnd,
+		.v_lines = options->v_lines,
+		.v_sync = V_SYNC_RQD,
+		.h_sync = (int) h_sync,
+		.v_front_porch = MIN_PORCH,
+		.v_back_porch = (int) v_back_porch,
+		.h_front_porch = (int) h_front_porch,
+		.h_back_porch = (int) (h_front_porch + h_sync),
+		.h_border = (int) h_margin,
+		.v_border = (int) v_margin,
+		.pixel_freq_mhz = pixel_freq,
+	};
+}

include/libdisplay-info/gtf.h

@@ -0,0 +1,72 @@
+#ifndef DI_GTF_H
+#define DI_GTF_H
+
+#include <stdbool.h>
+
+/**
+ * Low-level API for Generalized Timing Formula Standard version 1.1.
+ */
+
+/**
+ * Type of frequency parameter used in di_gtf_options.ip_freq_rqd.
+ */
+enum di_gtf_ip_param {
+	/* Vertical frame frequency (Hz) */
+	DI_GTF_IP_PARAM_V_FRAME_RATE,
+	/* Horizontal frequency (kHz) */
+	DI_GTF_IP_PARAM_H_FREQ,
+	/* Pixel clock rate (MHz) */
+	DI_GTF_IP_PARAM_H_PIXELS,
+};
+
+/**
+ * Input options for GTF.
+ */
+struct di_gtf_options {
+	/* Number of active image pixels displayed on a line, not including any
+	 * margin */
+	int h_pixels;
+	/* Number of vertical lines in the displayed image */
+	int v_lines;
+	/* Whether margins are required */
+	bool margins_rqd;
+	/* Indicates which frequency parameter is specified in ip_freq_rqd */
+	enum di_gtf_ip_param ip_param;
+	/* Vertical frame frequency (in Hz), horizontal frequency (in kHz) or
+	 * pixel clock rate (in MHz) */
+	double ip_freq_rqd;
+	/* Whether interlaced is required */
+	bool int_rqd;
+	/* Blanking formula gradient */
+	double m;
+	/* Blanking formula offset */
+	double c;
+	/* Blanking formula scaling factor */
+	double k;
+	/* Blanking formula scaling factor weighting */
+	double j;
+};
+
+#define DI_GTF_DEFAULT_M 600.0
+#define DI_GTF_DEFAULT_C 40.0
+#define DI_GTF_DEFAULT_K 128.0
+#define DI_GTF_DEFAULT_J 20.0
+
+/**
+ * Output timing data for GTF.
+ */
+struct di_gtf_timing {
+	int h_pixels, v_lines;
+	int h_sync, v_sync;
+	int h_front_porch, h_back_porch;
+	int v_front_porch, v_back_porch;
+	int h_border, v_border;
+	double pixel_freq_mhz; /* in mega-hertz */
+};
+
+/**
+ * Compute a timing via the GTF formula.
+ */
+void di_gtf_compute(struct di_gtf_timing *t, const struct di_gtf_options *options);
+
+#endif

meson.build

@@ -39,6 +39,7 @@ di_lib = library(
 		'displayid.c',
 		'dmt-table.c',
 		'edid.c',
+		'gtf.c',
 		'info.c',
 		'log.c',
 	],

test/data/acer-p1276.diff

@@ -1,18 +1,5 @@
 --- ref
 +++ di
-@@ -37,9 +37,9 @@
-     DMT 0x24:  1280x1024   75.024675 Hz   5:4     79.976 kHz    135.000000 MHz
-     Apple   :  1152x870    75.061550 Hz 192:145   68.681 kHz    100.000000 MHz
-   Standard Timings:
--    GTF     :   640x480   119.999084 Hz   4:3     61.800 kHz     52.406000 MHz
--    GTF     :   800x600   119.999886 Hz   4:3     77.160 kHz     83.950000 MHz
--    GTF     :  1024x768   119.999931 Hz   4:3     98.760 kHz    139.054000 MHz
-+    DMT 0x00:   640x480     0.000000 Hz   4:3      0.000 kHz      0.000000 MHz
-+    DMT 0x00:   800x600     0.000000 Hz   4:3      0.000 kHz      0.000000 MHz
-+    DMT 0x00:  1024x768     0.000000 Hz   4:3      0.000 kHz      0.000000 MHz
-     DMT 0x23:  1280x1024   60.019740 Hz   5:4     63.981 kHz    108.000000 MHz
-     DMT 0x33:  1600x1200   60.000000 Hz   4:3     75.000 kHz    162.000000 MHz
-     DMT 0x2f:  1440x900    59.887445 Hz  16:10    55.935 kHz    106.500000 MHz
 @@ -65,23 +65,8 @@
      DTD 2:  1366x768    59.789541 Hz 683:384   47.712 kHz     85.500000 MHz
                   Hfront   70 Hsync 143 Hback  213 Hpol P

test/data/goldstar-ite6604-hdmi.diff

@@ -1,6 +1,6 @@
 --- ref
 +++ di
-@@ -24,12 +24,12 @@
+@@ -24,7 +24,7 @@
      DMT 0x09:   800x600    60.316541 Hz   4:3     37.879 kHz     40.000000 MHz
      DMT 0x10:  1024x768    60.003840 Hz   4:3     48.363 kHz     65.000000 MHz
    Standard Timings:
@@ -9,12 +9,6 @@
      DMT 0x09:   800x600    60.316541 Hz   4:3     37.879 kHz     40.000000 MHz
      DMT 0x10:  1024x768    60.003840 Hz   4:3     48.363 kHz     65.000000 MHz
      DMT 0x23:  1280x1024   60.019740 Hz   5:4     63.981 kHz    108.000000 MHz
-     DMT 0x55:  1280x720    60.000000 Hz  16:9     45.000 kHz     74.250000 MHz
--    GTF     :  1368x769    60.000000 Hz  16:9     47.760 kHz     85.968000 MHz
-+    DMT 0x00:  1368x769     0.000000 Hz  16:9      0.000 kHz      0.000000 MHz
-     DMT 0x52:  1920x1080   60.000000 Hz  16:9     67.500 kHz    148.500000 MHz
-   Detailed Timing Descriptors:
-     DTD 1:  1920x1080   59.933878 Hz  16:9     66.587 kHz    138.500000 MHz (1000 mm x 550 mm)
 @@ -40,14 +40,14 @@
                   Vfront    3 Vsync   5 Vback   22 Vpol P
      Display Product Name: 'ITE6604'

test/data/sun-gh19ps-dvi.diff

@@ -1,16 +1,5 @@
 --- ref
 +++ di
-@@ -35,8 +35,8 @@
-     DMT 0x24:  1280x1024   75.024675 Hz   5:4     79.976 kHz    135.000000 MHz
-   Standard Timings:
-     DMT 0x23:  1280x1024   60.019740 Hz   5:4     63.981 kHz    108.000000 MHz
--    GTF     :  1280x1024   75.999957 Hz   5:4     81.320 kHz    141.822000 MHz
--    GTF     :  1152x921    66.000114 Hz   5:4     63.162 kHz     97.017000 MHz
-+    DMT 0x00:  1280x1024    0.000000 Hz   5:4      0.000 kHz      0.000000 MHz
-+    DMT 0x00:  1152x921     0.000000 Hz   5:4      0.000 kHz      0.000000 MHz
-     DMT 0x24:  1280x1024   75.024675 Hz   5:4     79.976 kHz    135.000000 MHz
-   Detailed Timing Descriptors:
-     DTD 1:  1280x1024   60.019740 Hz   5:4     63.981 kHz    108.000000 MHz (digital composite, serrate, 380 mm x 300 mm)
 @@ -50,15 +50,4 @@
  
  ----------------