1 /*
2  * Copyright 2005-2006 Luc Verhaegen.
3  * Copyright © 2021 Red Hat, Inc.
4  *
5  * Permission is hereby granted, free of charge, to any person obtaining a
6  * copy of this software and associated documentation files (the "Software"),
7  * to deal in the Software without restriction, including without limitation
8  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
9  * and/or sell copies of the Software, and to permit persons to whom the
10  * Software is furnished to do so, subject to the following conditions:
11  *
12  * The above copyright notice and this permission notice shall be included in
13  * all copies or substantial portions of the Software.
14  *
15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
18  * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
19  * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
20  * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
21  * OTHER DEALINGS IN THE SOFTWARE.
22  *
23  */
24 
25 /* Standalone VESA CVT standard timing modelines generator. */
26 
27 
28 #include <string.h>
29 #include <stdio.h>
30 #include <stdlib.h>
31 
32 #include <libxcvt/libxcvt.h>
33 
34 /*
35  * Generate a CVT standard mode from hdisplay, vdisplay and vrefresh.
36  *
37  * These calculations are stolen from the CVT calculation spreadsheet written
38  * by Graham Loveridge. He seems to be claiming no copyright and there seems to
39  * be no license attached to this. He apparently just wants to see his name
40  * mentioned.
41  *
42  * This file can be found at http://www.vesa.org/Public/CVT/CVTd6r1.xls
43  *
44  * Comments and structure corresponds to the comments and structure of the xls.
45  * This should ease importing of future changes to the standard (not very
46  * likely though).
47  *
48  * About margins; i'm sure that they are to be the bit between HDisplay and
49  * HBlankStart, HBlankEnd and HTotal, VDisplay and VBlankStart, VBlankEnd and
50  * VTotal, where the overscan colour is shown. FB seems to call _all_ blanking
51  * outside sync "margin" for some reason. Since we prefer seeing proper
52  * blanking instead of the overscan colour, and since the Crtc* values will
53  * probably get altered after us, we will disable margins altogether. With
54  * these calculations, Margins will plainly expand H/VDisplay, and we don't
55  * want that. -- libv
56  *
57  */
58 struct libxcvt_mode_info *
libxcvt_gen_mode_info(int hdisplay,int vdisplay,float vrefresh,bool reduced,bool interlaced)59 libxcvt_gen_mode_info(int hdisplay, int vdisplay, float vrefresh, bool reduced, bool interlaced)
60 {
61     bool margins = false;
62     float vfield_rate, hperiod;
63     int hdisplay_rnd, hmargin;
64     int vdisplay_rnd, vmargin, vsync;
65     float interlace;            /* Please rename this */
66     struct libxcvt_mode_info *mode_info;
67 
68     mode_info = calloc(1, sizeof *mode_info);
69     if (!mode_info)
70         return NULL;
71 
72     mode_info->hdisplay = hdisplay;
73     mode_info->vdisplay = vdisplay;
74     mode_info->vrefresh = vrefresh;
75 
76     /* 1) top/bottom margin size (% of height) - default: 1.8 */
77 #define CVT_MARGIN_PERCENTAGE 1.8
78 
79     /* 2) character cell horizontal granularity (pixels) - default 8 */
80 #define CVT_H_GRANULARITY 8
81 
82     /* 4) Minimum vertical porch (lines) - default 3 */
83 #define CVT_MIN_V_PORCH 3
84 
85     /* 4) Minimum number of vertical back porch lines - default 6 */
86 #define CVT_MIN_V_BPORCH 6
87 
88     /* Pixel Clock step (kHz) */
89 #define CVT_CLOCK_STEP 250
90 
91     /* CVT default is 60.0Hz */
92     if (!mode_info->vrefresh)
93         mode_info->vrefresh = 60.0;
94 
95     /* 1. Required field rate */
96     if (interlaced)
97         vfield_rate = mode_info->vrefresh * 2;
98     else
99         vfield_rate = mode_info->vrefresh;
100 
101     /* 2. Horizontal pixels */
102     hdisplay_rnd = mode_info->hdisplay - (mode_info->hdisplay % CVT_H_GRANULARITY);
103 
104     /* 3. Determine left and right borders */
105     if (margins) {
106         /* right margin is actually exactly the same as left */
107         hmargin = (((float) hdisplay_rnd) * CVT_MARGIN_PERCENTAGE / 100.0);
108         hmargin -= hmargin % CVT_H_GRANULARITY;
109     }
110     else {
111         hmargin = 0;
112     }
113 
114     /* 4. Find total active pixels */
115     mode_info->hdisplay = hdisplay_rnd + 2 * hmargin;
116 
117     /* 5. Find number of lines per field */
118     if (interlaced)
119         vdisplay_rnd = mode_info->vdisplay / 2;
120     else
121         vdisplay_rnd = mode_info->vdisplay;
122 
123     /* 6. Find top and bottom margins */
124     /* nope. */
125     if (margins)
126         /* top and bottom margins are equal again. */
127         vmargin = (((float) vdisplay_rnd) * CVT_MARGIN_PERCENTAGE / 100.0);
128     else
129         vmargin = 0;
130 
131     mode_info->vdisplay = mode_info->vdisplay + 2 * vmargin;
132 
133     /* 7. interlace */
134     if (interlaced)
135         interlace = 0.5;
136     else
137         interlace = 0.0;
138 
139     /* Determine vsync Width from aspect ratio */
140     if (!(mode_info->vdisplay % 3) && ((mode_info->vdisplay * 4 / 3) == mode_info->hdisplay))
141         vsync = 4;
142     else if (!(mode_info->vdisplay % 9) && ((mode_info->vdisplay * 16 / 9) == mode_info->hdisplay))
143         vsync = 5;
144     else if (!(mode_info->vdisplay % 10) && ((mode_info->vdisplay * 16 / 10) == mode_info->hdisplay))
145         vsync = 6;
146     else if (!(mode_info->vdisplay % 4) && ((mode_info->vdisplay * 5 / 4) == mode_info->hdisplay))
147         vsync = 7;
148     else if (!(mode_info->vdisplay % 9) && ((mode_info->vdisplay * 15 / 9) == mode_info->hdisplay))
149         vsync = 7;
150     else                        /* Custom */
151         vsync = 10;
152 
153     if (!reduced) {             /* simplified GTF calculation */
154 
155         /* 4) Minimum time of vertical sync + back porch interval (µs)
156          * default 550.0 */
157 #define CVT_MIN_VSYNC_BP 550.0
158 
159         /* 3) Nominal HSync width (% of line period) - default 8 */
160 #define CVT_HSYNC_PERCENTAGE 8
161 
162         float hblank_percentage;
163         int vsync_and_back_porch, vback_porch;
164         int hblank;
165 
166         /* 8. Estimated Horizontal period */
167         hperiod = ((float) (1000000.0 / vfield_rate - CVT_MIN_VSYNC_BP)) /
168             (vdisplay_rnd + 2 * vmargin + CVT_MIN_V_PORCH + interlace);
169 
170         /* 9. Find number of lines in sync + backporch */
171         if (((int) (CVT_MIN_VSYNC_BP / hperiod) + 1) <
172             (vsync + CVT_MIN_V_PORCH))
173             vsync_and_back_porch = vsync + CVT_MIN_V_PORCH;
174         else
175             vsync_and_back_porch = (int) (CVT_MIN_VSYNC_BP / hperiod) + 1;
176 
177         /* 10. Find number of lines in back porch */
178         vback_porch = vsync_and_back_porch - vsync;
179         (void) vback_porch;
180 
181         /* 11. Find total number of lines in vertical field */
182         mode_info->vtotal =
183             vdisplay_rnd + 2 * vmargin + vsync_and_back_porch + interlace +
184             CVT_MIN_V_PORCH;
185 
186         /* 5) Definition of Horizontal blanking time limitation */
187         /* Gradient (%/kHz) - default 600 */
188 #define CVT_M_FACTOR 600
189 
190         /* Offset (%) - default 40 */
191 #define CVT_C_FACTOR 40
192 
193         /* Blanking time scaling factor - default 128 */
194 #define CVT_K_FACTOR 128
195 
196         /* Scaling factor weighting - default 20 */
197 #define CVT_J_FACTOR 20
198 
199 #define CVT_M_PRIME CVT_M_FACTOR * CVT_K_FACTOR / 256
200 #define CVT_C_PRIME (CVT_C_FACTOR - CVT_J_FACTOR) * CVT_K_FACTOR / 256 + \
201         CVT_J_FACTOR
202 
203         /* 12. Find ideal blanking duty cycle from formula */
204         hblank_percentage = CVT_C_PRIME - CVT_M_PRIME * hperiod / 1000.0;
205 
206         /* 13. Blanking time */
207         if (hblank_percentage < 20)
208             hblank_percentage = 20;
209 
210         hblank = mode_info->hdisplay * hblank_percentage / (100.0 - hblank_percentage);
211         hblank -= hblank % (2 * CVT_H_GRANULARITY);
212 
213         /* 14. Find total number of pixels in a line. */
214         mode_info->htotal = mode_info->hdisplay + hblank;
215 
216         /* Fill in HSync values */
217         mode_info->hsync_end = mode_info->hdisplay + hblank / 2;
218 
219         mode_info->hsync_start = mode_info->hsync_end -
220             (mode_info->htotal * CVT_HSYNC_PERCENTAGE) / 100;
221         mode_info->hsync_start += CVT_H_GRANULARITY -
222             mode_info->hsync_start % CVT_H_GRANULARITY;
223 
224         /* Fill in vsync values */
225         mode_info->vsync_start = mode_info->vdisplay + CVT_MIN_V_PORCH;
226         mode_info->vsync_end = mode_info->vsync_start + vsync;
227 
228     }
229     else {                      /* reduced blanking */
230         /* Minimum vertical blanking interval time (µs) - default 460 */
231 #define CVT_RB_MIN_VBLANK 460.0
232 
233         /* Fixed number of clocks for horizontal sync */
234 #define CVT_RB_H_SYNC 32.0
235 
236         /* Fixed number of clocks for horizontal blanking */
237 #define CVT_RB_H_BLANK 160.0
238 
239         /* Fixed number of lines for vertical front porch - default 3 */
240 #define CVT_RB_VFPORCH 3
241 
242         int vblank_interval_lines;
243 
244         /* 8. Estimate Horizontal period. */
245         hperiod = ((float) (1000000.0 / vfield_rate - CVT_RB_MIN_VBLANK)) /
246             (vdisplay_rnd + 2 * vmargin);
247 
248         /* 9. Find number of lines in vertical blanking */
249         vblank_interval_lines = ((float) CVT_RB_MIN_VBLANK) / hperiod + 1;
250 
251         /* 10. Check if vertical blanking is sufficient */
252         if (vblank_interval_lines < (CVT_RB_VFPORCH + vsync + CVT_MIN_V_BPORCH))
253             vblank_interval_lines = CVT_RB_VFPORCH + vsync + CVT_MIN_V_BPORCH;
254 
255         /* 11. Find total number of lines in vertical field */
256         mode_info->vtotal = vdisplay_rnd + 2 * vmargin + interlace + vblank_interval_lines;
257 
258         /* 12. Find total number of pixels in a line */
259         mode_info->htotal = mode_info->hdisplay + CVT_RB_H_BLANK;
260 
261         /* Fill in HSync values */
262         mode_info->hsync_end = mode_info->hdisplay + CVT_RB_H_BLANK / 2;
263         mode_info->hsync_start = mode_info->hsync_end - CVT_RB_H_SYNC;
264 
265         /* Fill in vsync values */
266         mode_info->vsync_start = mode_info->vdisplay + CVT_RB_VFPORCH;
267         mode_info->vsync_end = mode_info->vsync_start + vsync;
268     }
269 
270     /* 15/13. Find pixel clock frequency (kHz for xf86) */
271     mode_info->dot_clock = mode_info->htotal * 1000.0 / hperiod;
272     mode_info->dot_clock -= mode_info->dot_clock % CVT_CLOCK_STEP;
273 
274     /* 16/14. Find actual Horizontal Frequency (kHz) */
275     mode_info->hsync = ((float) mode_info->dot_clock) / ((float) mode_info->htotal);
276 
277     /* 17/15. Find actual Field rate */
278     mode_info->vrefresh = (1000.0 * ((float) mode_info->dot_clock)) /
279         ((float) (mode_info->htotal * mode_info->vtotal));
280 
281     /* 18/16. Find actual vertical frame frequency */
282     /* ignore - just set the mode flag for interlaced */
283     if (interlaced)
284         mode_info->vtotal *= 2;
285 
286     if (reduced)
287         mode_info->mode_flags |= LIBXCVT_MODE_FLAG_HSYNC_POSITIVE | LIBXCVT_MODE_FLAG_VSYNC_NEGATIVE;
288     else
289         mode_info->mode_flags |= LIBXCVT_MODE_FLAG_HSYNC_NEGATIVE | LIBXCVT_MODE_FLAG_VSYNC_POSITIVE;
290 
291     if (interlaced)
292         mode_info->mode_flags |= LIBXCVT_MODE_FLAG_INTERLACE;
293 
294     /* FWXGA hack adapted from hw/xfree86/modes/xf86EdidModes.c, because you can't say 1366 */
295     if (mode_info->hdisplay == 1366 && mode_info->vdisplay == 768) {
296          mode_info->hsync_start--;
297          mode_info->hsync_end--;
298     }
299 
300     return mode_info;
301 }
302