drm/i915: Fix FDI M/N setting according with correct color depth
FDI M/N calculation hasn't taken the current pipe color depth into account,
but always set as 24bpp. This one checks current pipe color depth setting,
and change FDI M/N calculation a little to use bits_per_pixel first, then
convert to bytes_per_pixel later.
This fixes display corrupt issue on Arrandle LVDS with 1600x900 panel
in 18bpp dual-channel mode.
Cc: Stable Team <stable@kernel.org>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index be7fada..8278d9d 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -2082,7 +2082,7 @@
#define LINK_N 0x80000
static void
-igdng_compute_m_n(int bytes_per_pixel, int nlanes,
+igdng_compute_m_n(int bits_per_pixel, int nlanes,
int pixel_clock, int link_clock,
struct fdi_m_n *m_n)
{
@@ -2092,7 +2092,8 @@
temp = (u64) DATA_N * pixel_clock;
temp = div_u64(temp, link_clock);
- m_n->gmch_m = div_u64(temp * bytes_per_pixel, nlanes);
+ m_n->gmch_m = div_u64(temp * bits_per_pixel, nlanes);
+ m_n->gmch_m >>= 3; /* convert to bytes_per_pixel */
m_n->gmch_n = DATA_N;
fdi_reduce_ratio(&m_n->gmch_m, &m_n->gmch_n);
@@ -2766,7 +2767,7 @@
/* FDI link */
if (IS_IGDNG(dev)) {
- int lane, link_bw;
+ int lane, link_bw, bpp;
/* eDP doesn't require FDI link, so just set DP M/N
according to current link config */
if (is_edp) {
@@ -2785,7 +2786,29 @@
lane = 4;
link_bw = 270000;
}
- igdng_compute_m_n(3, lane, target_clock,
+
+ /* determine panel color depth */
+ temp = I915_READ(pipeconf_reg);
+
+ switch (temp & PIPE_BPC_MASK) {
+ case PIPE_8BPC:
+ bpp = 24;
+ break;
+ case PIPE_10BPC:
+ bpp = 30;
+ break;
+ case PIPE_6BPC:
+ bpp = 18;
+ break;
+ case PIPE_12BPC:
+ bpp = 36;
+ break;
+ default:
+ DRM_ERROR("unknown pipe bpc value\n");
+ bpp = 24;
+ }
+
+ igdng_compute_m_n(bpp, lane, target_clock,
link_bw, &m_n);
}