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   1 /*
   2  *  linux/include/asm-arm/arch-rpc/acornfb.h
   3  *
   4  *  Copyright (C) 1999 Russell King
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License version 2 as
   8  * published by the Free Software Foundation.
   9  *
  10  *  AcornFB architecture specific code
  11  */
  12
  13 #define acornfb_bandwidth(var) ((var)->pixclock * 8 / (var)->bits_per_pixel)
  14
  15 static inline int
  16 acornfb_valid_pixrate(struct fb_var_screeninfo *var)
  17 {
  18         u_long limit;
  19
  20         if (!var->pixclock)
  21                 return 0;
  22
  23         /*
  24          * Limits below are taken from RISC OS bandwidthlimit file
  25          */
  26         if (current_par.using_vram) {
  27                 if (current_par.vram_half_sam == 2048)
  28                         limit = 6578;
  29                 else
  30                         limit = 13157;
  31         } else {
  32                 limit = 26315;
  33         }
  34
  35         return acornfb_bandwidth(var) >= limit;
  36 }
  37
  38 /*
  39  * Try to find the best PLL parameters for the pixel clock.
  40  * This algorithm seems to give best predictable results,
  41  * and produces the same values as detailed in the VIDC20
  42  * data sheet.
  43  */
  44 static inline u_int
  45 acornfb_vidc20_find_pll(u_int pixclk)
  46 {
  47         u_int r, best_r = 2, best_v = 2;
  48         int best_d = 0x7fffffff;
  49
  50         for (r = 2; r <= 32; r++) {
  51                 u_int rr, v, p;
  52                 int d;
  53
  54                 rr = 41667 * r;
  55
  56                 v = (rr + pixclk / 2) / pixclk;
  57
  58                 if (v > 32 || v < 2)
  59                         continue;
  60
  61                 p = (rr + v / 2) / v;
  62
  63                 d = pixclk - p;
  64
  65                 if (d < 0)
  66                         d = -d;
  67
  68                 if (d < best_d) {
  69                         best_d = d;
  70                         best_v = v - 1;
  71                         best_r = r - 1;
  72                 }
  73
  74                 if (d == 0)
  75                         break;
  76         }
  77
  78         return best_v << 8 | best_r;
  79 }
  80
  81 static inline void
  82 acornfb_vidc20_find_rates(struct vidc_timing *vidc,
  83                           struct fb_var_screeninfo *var)
  84 {
  85         u_int div;
  86
  87         /* Select pixel-clock divisor to keep PLL in range */
  88         div = var->pixclock / 9090; /*9921*/
  89
  90         /* Limit divisor */
  91         if (div == 0)
  92                 div = 1;
  93         if (div > 8)
  94                 div = 8;
  95
  96         /* Encode divisor to VIDC20 setting */
  97         switch (div) {
  98         case 1: vidc->control |= VIDC20_CTRL_PIX_CK;  break;
  99         case 2: vidc->control |= VIDC20_CTRL_PIX_CK2; break;
 100         case 3: vidc->control |= VIDC20_CTRL_PIX_CK3; break;
 101         case 4: vidc->control |= VIDC20_CTRL_PIX_CK4; break;
 102         case 5: vidc->control |= VIDC20_CTRL_PIX_CK5; break;
 103         case 6: vidc->control |= VIDC20_CTRL_PIX_CK6; break;
 104         case 7: vidc->control |= VIDC20_CTRL_PIX_CK7; break;
 105         case 8: vidc->control |= VIDC20_CTRL_PIX_CK8; break;
 106         }
 107
 108         /*
 109          * With VRAM, the FIFO can be set to the highest possible setting
 110          * because there are no latency considerations for other memory
 111          * accesses. However, in 64 bit bus mode the FIFO preload value
 112          * must not be set to VIDC20_CTRL_FIFO_28 because this will let
 113          * the FIFO overflow. See VIDC20 manual page 33 (6.0 Setting the
 114          * FIFO preload value).
 115          */
 116         if (current_par.using_vram) {
 117                 if (current_par.vram_half_sam == 2048)
 118                         vidc->control |= VIDC20_CTRL_FIFO_24;
 119                 else
 120                         vidc->control |= VIDC20_CTRL_FIFO_28;
 121         } else {
 122                 unsigned long bandwidth = acornfb_bandwidth(var);
 123
 124                 /* Encode bandwidth as VIDC20 setting */
 125                 if (bandwidth > 33334)          /* < 30.0MB/s */
 126                         vidc->control |= VIDC20_CTRL_FIFO_16;
 127                 else if (bandwidth > 26666)     /* < 37.5MB/s */
 128                         vidc->control |= VIDC20_CTRL_FIFO_20;
 129                 else if (bandwidth > 22222)     /* < 45.0MB/s */
 130                         vidc->control |= VIDC20_CTRL_FIFO_24;
 131                 else                            /* > 45.0MB/s */
 132                         vidc->control |= VIDC20_CTRL_FIFO_28;
 133         }
 134
 135         /* Find the PLL values */
 136         vidc->pll_ctl = acornfb_vidc20_find_pll(var->pixclock / div);
 137 }
 138
 139 #define acornfb_default_control()       (VIDC20_CTRL_PIX_VCLK)
 140 #define acornfb_default_econtrol()      (VIDC20_ECTL_DAC | VIDC20_ECTL_REG(3))