[PATCH] fbdev: Add VESA Coordinated Video Timings (CVT) support

The Coordinated Video Timings (CVT) is the latest standard approved by VESA
concerning video timings generation.  It addresses the limitation of GTF which
is designed mainly for CRT displays.  CRT's have a high blanking requirement
(as much as 25% of the horizontal frame length) which artificially increases
the pixelclock.  Digital displays, on the other hand, needs to conserve the
pixelclock as much as possible.  The GTF also does not take into account the
different aspect ratios in its calculation.

The new function added is fb_find_mode_cvt().  It is called by fb_find_mode()
if it recognizes a mode option string formatted for CVT.  The format is:

<xres>x<yres>[M][R][-<bpp>][<at-sign><refresh>][i][m]

The 'M' tells the function to calculate using CVT.  On it's own, it will
compute a timing for CRT displays at 60Hz.  If the 'R' is specified, 'reduced
blanking' computation will be used, best for flatpanels.  The 'i' and the 'm'
is for 'interlaced mode' and 'with margins' respectively.

To determine if CVT was used, check for dmesg for something like this:

CVT Mode - <pix>M<n>[-R], ie: .480M3-R  (800x600 reduced blanking)

where: pix - product of xres and yres, in MB
    M   - is a CVT mode
    n   - the aspect ratio (3 - 4:3; 4 - 5:4; 9 - 16:9, 15:9; A - 16:10)
    -R   - reduced blanking

Signed-off-by: Antonino Daplas <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 380 insertions, 0 deletions

diff --git a/drivers/video/fbcvt.c b/drivers/video/fbcvt.c
new file mode 100644
index 00000000000..cfa61b512de
--- /dev/null
+++ b/drivers/video/fbcvt.c
@@ -0,0 +1,380 @@
+/*
+ * linux/drivers/video/fbcvt.c - VESA(TM) Coordinated Video Timings
+ *
+ * Copyright (C) 2005 Antonino Daplas <adaplas@pol.net>
+ *
+ *      Based from the VESA(TM) Coordinated Video Timing Generator by
+ *      Graham Loveridge April 9, 2003 available at
+ *      http://www.vesa.org/public/CVT/CVTd6r1.xls
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file COPYING in the main directory of this archive
+ * for more details.
+ *
+ */
+#include <linux/fb.h>
+
+#define FB_CVT_CELLSIZE               8
+#define FB_CVT_GTF_C                 40
+#define FB_CVT_GTF_J                 20
+#define FB_CVT_GTF_K                128
+#define FB_CVT_GTF_M                600
+#define FB_CVT_MIN_VSYNC_BP         550
+#define FB_CVT_MIN_VPORCH             3
+#define FB_CVT_MIN_BPORCH             6
+
+#define FB_CVT_RB_MIN_VBLANK        460
+#define FB_CVT_RB_HBLANK            160
+#define FB_CVT_RB_V_FPORCH            3
+
+#define FB_CVT_FLAG_REDUCED_BLANK 1
+#define FB_CVT_FLAG_MARGINS       2
+#define FB_CVT_FLAG_INTERLACED    4
+
+struct fb_cvt_data {
+        u32 xres;
+        u32 yres;
+        u32 refresh;
+        u32 f_refresh;
+        u32 pixclock;
+        u32 hperiod;
+        u32 hblank;
+        u32 hfreq;
+        u32 htotal;
+        u32 vtotal;
+        u32 vsync;
+        u32 hsync;
+        u32 h_front_porch;
+        u32 h_back_porch;
+        u32 v_front_porch;
+        u32 v_back_porch;
+        u32 h_margin;
+        u32 v_margin;
+        u32 interlace;
+        u32 aspect_ratio;
+        u32 active_pixels;
+        u32 flags;
+        u32 status;
+};
+
+static int fb_cvt_vbi_tab[] = {
+        4,        /* 4:3      */
+        5,        /* 16:9     */
+        6,        /* 16:10    */
+        7,        /* 5:4      */
+        7,        /* 15:9     */
+        8,        /* reserved */
+        9,        /* reserved */
+        10        /* custom   */
+};
+
+/* returns hperiod * 1000 */
+static u32 fb_cvt_hperiod(struct fb_cvt_data *cvt)
+{
+        u32 num = 1000000000/cvt->f_refresh;
+        u32 den;
+
+        if (cvt->flags & FB_CVT_FLAG_REDUCED_BLANK) {
+                num -= FB_CVT_RB_MIN_VBLANK * 1000;
+                den = 2 * (cvt->yres/cvt->interlace + 2 * cvt->v_margin);
+        } else {
+                num -= FB_CVT_MIN_VSYNC_BP * 1000;
+                den = 2 * (cvt->yres/cvt->interlace + cvt->v_margin * 2
+                           + FB_CVT_MIN_VPORCH + cvt->interlace/2);
+        }
+
+        return 2 * (num/den);
+}
+
+/* returns ideal duty cycle * 1000 */
+static u32 fb_cvt_ideal_duty_cycle(struct fb_cvt_data *cvt)
+{
+        u32 c_prime = (FB_CVT_GTF_C - FB_CVT_GTF_J) *
+                (FB_CVT_GTF_K) + 256 * FB_CVT_GTF_J;
+        u32 m_prime = (FB_CVT_GTF_K * FB_CVT_GTF_M);
+        u32 h_period_est = cvt->hperiod;
+
+        return (1000 * c_prime  - ((m_prime * h_period_est)/1000))/256;
+}
+
+static u32 fb_cvt_hblank(struct fb_cvt_data *cvt)
+{
+        u32 hblank = 0;
+
+        if (cvt->flags & FB_CVT_FLAG_REDUCED_BLANK)
+                hblank = FB_CVT_RB_HBLANK;
+        else {
+                u32 ideal_duty_cycle = fb_cvt_ideal_duty_cycle(cvt);
+                u32 active_pixels = cvt->active_pixels;
+
+                if (ideal_duty_cycle < 20000)
+                        hblank = (active_pixels * 20000)/
+                                (100000 - 20000);
+                else {
+                        hblank = (active_pixels * ideal_duty_cycle)/
+                                (100000 - ideal_duty_cycle);
+                }
+        }
+
+        hblank &= ~((2 * FB_CVT_CELLSIZE) - 1);
+
+        return hblank;
+}
+
+static u32 fb_cvt_hsync(struct fb_cvt_data *cvt)
+{
+        u32 hsync;
+
+        if (cvt->flags & FB_CVT_FLAG_REDUCED_BLANK)
+                hsync = 32;
+        else
+                hsync = (FB_CVT_CELLSIZE * cvt->htotal)/100;
+
+        hsync &= ~(FB_CVT_CELLSIZE - 1);
+        return hsync;
+}
+
+static u32 fb_cvt_vbi_lines(struct fb_cvt_data *cvt)
+{
+        u32 vbi_lines, min_vbi_lines, act_vbi_lines;
+
+        if (cvt->flags & FB_CVT_FLAG_REDUCED_BLANK) {
+                vbi_lines = (1000 * FB_CVT_RB_MIN_VBLANK)/cvt->hperiod + 1;
+                min_vbi_lines =  FB_CVT_RB_V_FPORCH + cvt->vsync +
+                        FB_CVT_MIN_BPORCH;
+
+        } else {
+                vbi_lines = (FB_CVT_MIN_VSYNC_BP * 1000)/cvt->hperiod + 1 +
+                         FB_CVT_MIN_VPORCH;
+                min_vbi_lines = cvt->vsync + FB_CVT_MIN_BPORCH +
+                        FB_CVT_MIN_VPORCH;
+        }
+
+        if (vbi_lines < min_vbi_lines)
+                act_vbi_lines = min_vbi_lines;
+        else
+                act_vbi_lines = vbi_lines;
+
+        return act_vbi_lines;
+}
+
+static u32 fb_cvt_vtotal(struct fb_cvt_data *cvt)
+{
+        u32 vtotal = cvt->yres/cvt->interlace;
+
+        vtotal += 2 * cvt->v_margin + cvt->interlace/2 + fb_cvt_vbi_lines(cvt);
+        vtotal |= cvt->interlace/2;
+
+        return vtotal;
+}
+
+static u32 fb_cvt_pixclock(struct fb_cvt_data *cvt)
+{
+        u32 pixclock;
+
+        if (cvt->flags & FB_CVT_FLAG_REDUCED_BLANK)
+                pixclock = (cvt->f_refresh * cvt->vtotal * cvt->htotal)/1000;
+        else
+                pixclock = (cvt->htotal * 1000000)/cvt->hperiod;
+
+        pixclock /= 250;
+        pixclock *= 250;
+        pixclock *= 1000;
+
+        return pixclock;
+}
+
+static u32 fb_cvt_aspect_ratio(struct fb_cvt_data *cvt)
+{
+        u32 xres = cvt->xres;
+        u32 yres = cvt->yres;
+        u32 aspect = -1;
+
+        if (xres == (yres * 4)/3 && !((yres * 4) % 3))
+                aspect = 0;
+        else if (xres == (yres * 16)/9 && !((yres * 16) % 9))
+                aspect = 1;
+        else if (xres == (yres * 16)/10 && !((yres * 16) % 10))
+                aspect = 2;
+        else if (xres == (yres * 5)/4 && !((yres * 5) % 4))
+                aspect = 3;
+        else if (xres == (yres * 15)/9 && !((yres * 15) % 9))
+                aspect = 4;
+        else {
+                printk(KERN_INFO "fbcvt: Aspect ratio not CVT "
+                       "standard\n");
+                aspect = 7;
+                cvt->status = 1;
+        }
+
+        return aspect;
+}
+
+static void fb_cvt_print_name(struct fb_cvt_data *cvt)
+{
+        u32 pixcount, pixcount_mod;
+        int cnt = 255, offset = 0, read = 0;
+        u8 *buf = kmalloc(256, GFP_KERNEL);
+
+        if (!buf)
+                return;
+
+        memset(buf, 0, 256);
+        pixcount = (cvt->xres * (cvt->yres/cvt->interlace))/1000000;
+        pixcount_mod = (cvt->xres * (cvt->yres/cvt->interlace)) % 1000000;
+        pixcount_mod /= 1000;
+
+        read = snprintf(buf+offset, cnt, "fbcvt: %dx%d@%d: CVT Name - ",
+                        cvt->xres, cvt->yres, cvt->refresh);
+        offset += read;
+        cnt -= read;
+
+        if (cvt->status)
+                snprintf(buf+offset, cnt, "Not a CVT standard - %d.%03d Mega "
+                         "Pixel Image\n", pixcount, pixcount_mod);
+        else {
+                if (pixcount) {
+                        read = snprintf(buf+offset, cnt, "%d", pixcount);
+                        cnt -= read;
+                        offset += read;
+                }
+
+                read = snprintf(buf+offset, cnt, ".%03dM", pixcount_mod);
+                cnt -= read;
+                offset += read;
+
+                if (cvt->aspect_ratio == 0)
+                        read = snprintf(buf+offset, cnt, "3");
+                else if (cvt->aspect_ratio == 3)
+                        read = snprintf(buf+offset, cnt, "4");
+                else if (cvt->aspect_ratio == 1 || cvt->aspect_ratio == 4)
+                        read = snprintf(buf+offset, cnt, "9");
+                else if (cvt->aspect_ratio == 2)
+                        read = snprintf(buf+offset, cnt, "A");
+                else
+                        read = 0;
+                cnt -= read;
+                offset += read;
+
+                if (cvt->flags & FB_CVT_FLAG_REDUCED_BLANK) {
+                        read = snprintf(buf+offset, cnt, "-R");
+                        cnt -= read;
+                        offset += read;
+                }
+        }
+
+        printk(KERN_INFO "%s\n", buf);
+        kfree(buf);
+}
+
+static void fb_cvt_convert_to_mode(struct fb_cvt_data *cvt,
+                                   struct fb_videomode *mode)
+{
+        mode->refresh = cvt->f_refresh;
+        mode->pixclock = KHZ2PICOS(cvt->pixclock/1000);
+        mode->left_margin = cvt->h_front_porch;
+        mode->right_margin = cvt->h_back_porch;
+        mode->hsync_len = cvt->hsync;
+        mode->upper_margin = cvt->v_front_porch;
+        mode->lower_margin = cvt->v_back_porch;
+        mode->vsync_len = cvt->vsync;
+
+        mode->sync &= ~(FB_SYNC_HOR_HIGH_ACT | FB_SYNC_VERT_HIGH_ACT);
+
+        if (cvt->flags & FB_CVT_FLAG_REDUCED_BLANK)
+                mode->sync |= FB_SYNC_HOR_HIGH_ACT;
+        else
+                mode->sync |= FB_SYNC_VERT_HIGH_ACT;
+}
+
+/*
+ * fb_find_mode_cvt - calculate mode using VESA(TM) CVT
+ * @mode: pointer to fb_videomode; xres, yres, refresh and vmode must be
+ *        pre-filled with the desired values
+ * @margins: add margin to calculation (1.8% of xres and yres)
+ * @rb: compute with reduced blanking (for flatpanels)
+ *
+ * RETURNS:
+ * 0 for success
+ * @mode is filled with computed values.  If interlaced, the refresh field
+ * will be filled with the field rate (2x the frame rate)
+ *
+ * DESCRIPTION:
+ * Computes video timings using VESA(TM) Coordinated Video Timings
+ */
+int fb_find_mode_cvt(struct fb_videomode *mode, int margins, int rb)
+{
+        struct fb_cvt_data cvt;
+
+        memset(&cvt, 0, sizeof(cvt));
+
+        if (margins)
+            cvt.flags |= FB_CVT_FLAG_MARGINS;
+
+        if (rb)
+            cvt.flags |= FB_CVT_FLAG_REDUCED_BLANK;
+
+        if (mode->vmode & FB_VMODE_INTERLACED)
+            cvt.flags |= FB_CVT_FLAG_INTERLACED;
+
+        cvt.xres = mode->xres;
+        cvt.yres = mode->yres;
+        cvt.refresh = mode->refresh;
+        cvt.f_refresh = cvt.refresh;
+        cvt.interlace = 1;
+
+        if (!cvt.xres || !cvt.yres || !cvt.refresh) {
+                printk(KERN_INFO "fbcvt: Invalid input parameters\n");
+                return 1;
+        }
+
+        if (!(cvt.refresh == 50 || cvt.refresh == 60 || cvt.refresh == 70 ||
+              cvt.refresh == 85)) {
+                printk(KERN_INFO "fbcvt: Refresh rate not CVT "
+                       "standard\n");
+                cvt.status = 1;
+        }
+
+        cvt.xres &= ~(FB_CVT_CELLSIZE - 1);
+
+        if (cvt.flags & FB_CVT_FLAG_INTERLACED) {
+                cvt.interlace = 2;
+                cvt.f_refresh *= 2;
+        }
+
+        if (cvt.flags & FB_CVT_FLAG_REDUCED_BLANK) {
+                if (cvt.refresh != 60) {
+                        printk(KERN_INFO "fbcvt: 60Hz refresh rate "
+                               "advised for reduced blanking\n");
+                        cvt.status = 1;
+                }
+        }
+
+        if (cvt.flags & FB_CVT_FLAG_MARGINS) {
+                cvt.h_margin = (cvt.xres * 18)/1000;
+                cvt.h_margin &= ~(FB_CVT_CELLSIZE - 1);
+                cvt.v_margin = ((cvt.yres/cvt.interlace)* 18)/1000;
+        }
+
+        cvt.aspect_ratio = fb_cvt_aspect_ratio(&cvt);
+        cvt.active_pixels = cvt.xres + 2 * cvt.h_margin;
+        cvt.hperiod = fb_cvt_hperiod(&cvt);
+        cvt.vsync = fb_cvt_vbi_tab[cvt.aspect_ratio];
+        cvt.vtotal = fb_cvt_vtotal(&cvt);
+        cvt.hblank = fb_cvt_hblank(&cvt);
+        cvt.htotal = cvt.active_pixels + cvt.hblank;
+        cvt.hsync = fb_cvt_hsync(&cvt);
+        cvt.pixclock = fb_cvt_pixclock(&cvt);
+        cvt.hfreq = cvt.pixclock/cvt.htotal;
+        cvt.h_back_porch = cvt.hblank/2 + cvt.h_margin;
+        cvt.h_front_porch = cvt.hblank - cvt.hsync - cvt.h_back_porch +
+                2 * cvt.h_margin;
+        cvt.v_back_porch = 3 + cvt.v_margin;
+        cvt.v_front_porch = cvt.vtotal - cvt.yres/cvt.interlace -
+            cvt.v_back_porch - cvt.vsync;
+        fb_cvt_print_name(&cvt);
+        fb_cvt_convert_to_mode(&cvt, mode);
+
+        return 0;
+}
+EXPORT_SYMBOL(fb_find_mode_cvt);