cirrusfb: fix clock doubling

Cirrus' Alpine and Picasso4 chips uses DAC clock doubling to achieve full
range of pixclock frequencies.

[akpm@linux-foundation.org: fix spelling, use usual comment layout]
Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 18 insertions, 1 deletions

diff --git a/drivers/video/cirrusfb.c b/drivers/video/cirrusfb.c
index 65a1831ddd0d..15e2e6bfcbff 100644
--- a/drivers/video/cirrusfb.c
+++ b/drivers/video/cirrusfb.c
@@ -470,10 +470,25 @@ static int cirrusfb_check_pixclock(const struct fb_var_screeninfo *var,
         /* If the frequency is greater than we can support, we might be able
          * to use multiplexing for the video mode */
         if (freq > maxclock) {
+                dev_err(info->device,
+                        "Frequency greater than maxclock (%ld kHz)\n",
+                        maxclock);
+                return -EINVAL;
+        }
+        /*
+         * Additional constraint: 8bpp uses DAC clock doubling to allow maximum
+         * pixel clock
+         */
+        if (var->bits_per_pixel == 8) {
                 switch (cinfo->btype) {
                 case BT_ALPINE:
+                case BT_PICASSO4:
+                        if (freq > 85500)
+                                cinfo->multiplexing = 1;
+                        break;
                 case BT_GD5480:
-                        cinfo->multiplexing = 1;
+                        if (freq > 135100)
+                                cinfo->multiplexing = 1;
                         break;
 
                 default:
@@ -815,6 +830,8 @@ static int cirrusfb_set_par_foo(struct fb_info *info)
         freq = PICOS2KHZ(var->pixclock);
         if (cinfo->btype == BT_ALPINE && var->bits_per_pixel == 24)
                 freq *= 3;
+        if (cinfo->multiplexing)
+                freq /= 2;
 
         bestclock(freq, &nom, &den, &div);