Reuse what is programmed by pre-os, but in case there is no pre-os
initialization, init the cdclk with the max value by default untill
dynamic cdclk support comes.

v2: Check if BIOS programmed correctly rather than always calling init
    - Do validation of programmed cdctl and what it is expected
    - Only do slk_init_cdclk if validation failed else reuse BIOS
      programmed value

Cc: Imre Deak <imre.d...@intel.com>
Cc: Ville Syrjälä <ville.syrj...@linux.intel.com>
Signed-off-by: Shobhit Kumar <shobhit.ku...@intel.com>
---
 drivers/gpu/drm/i915/intel_ddi.c     | 18 ++++++++++++-----
 drivers/gpu/drm/i915/intel_display.c | 39 +++++++++++++++++++++++++++---------
 2 files changed, 42 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
index 2d3cc82..3ec5618 100644
--- a/drivers/gpu/drm/i915/intel_ddi.c
+++ b/drivers/gpu/drm/i915/intel_ddi.c
@@ -2946,11 +2946,19 @@ void intel_ddi_pll_init(struct drm_device *dev)
                int cdclk_freq;
 
                cdclk_freq = dev_priv->display.get_display_clock_speed(dev);
-               dev_priv->skl_boot_cdclk = cdclk_freq;
-               if (!(I915_READ(LCPLL1_CTL) & LCPLL_PLL_ENABLE))
-                       DRM_ERROR("LCPLL1 is disabled\n");
-               else
-                       intel_display_power_get(dev_priv, POWER_DOMAIN_PLLS);
+
+               /* Invalid CDCLK from BIOS ? */
+               if (cdclk_freq < 0) {
+                       /* program to maximum cdclk till we have dynamic cdclk 
support */
+                       dev_priv->skl_boot_cdclk = 675000;
+                       skl_init_cdclk(dev_priv);
+               } else {
+                       dev_priv->skl_boot_cdclk = cdclk_freq;
+                       if (!(I915_READ(LCPLL1_CTL) & LCPLL_PLL_ENABLE))
+                               DRM_ERROR("LCPLL1 is disabled\n");
+                       else
+                               intel_display_power_get(dev_priv, 
POWER_DOMAIN_PLLS);
+               }
        } else if (IS_BROXTON(dev)) {
                broxton_init_cdclk(dev);
                broxton_ddi_phy_init(dev);
diff --git a/drivers/gpu/drm/i915/intel_display.c 
b/drivers/gpu/drm/i915/intel_display.c
index bbeb6d3..f734410 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -6634,12 +6634,15 @@ static int skylake_get_display_clock_speed(struct 
drm_device *dev)
        uint32_t lcpll1 = I915_READ(LCPLL1_CTL);
        uint32_t cdctl = I915_READ(CDCLK_CTL);
        uint32_t linkrate;
+       int freq;
 
        if (!(lcpll1 & LCPLL_PLL_ENABLE))
                return 24000; /* 24MHz is the cd freq with NSSC ref */
 
-       if ((cdctl & CDCLK_FREQ_SEL_MASK) == CDCLK_FREQ_540)
-               return 540000;
+       if ((cdctl & CDCLK_FREQ_SEL_MASK) == CDCLK_FREQ_540) {
+               freq = 540000;
+               goto verify;
+       }
 
        linkrate = (I915_READ(DPLL_CTRL1) &
                    DPLL_CTRL1_LINK_RATE_MASK(SKL_DPLL0)) >> 1;
@@ -6649,30 +6652,46 @@ static int skylake_get_display_clock_speed(struct 
drm_device *dev)
                /* vco 8640 */
                switch (cdctl & CDCLK_FREQ_SEL_MASK) {
                case CDCLK_FREQ_450_432:
-                       return 432000;
+                       freq = 432000;
+                       break;
                case CDCLK_FREQ_337_308:
-                       return 308570;
+                       freq = 308570;
+                       break;
                case CDCLK_FREQ_675_617:
-                       return 617140;
+                       freq = 617140;
+                       break;
                default:
                        WARN(1, "Unknown cd freq selection\n");
+                       return -EINVAL;
                }
        } else {
                /* vco 8100 */
                switch (cdctl & CDCLK_FREQ_SEL_MASK) {
                case CDCLK_FREQ_450_432:
-                       return 450000;
+                       freq = 450000;
+                       break;
                case CDCLK_FREQ_337_308:
-                       return 337500;
+                       freq = 337500;
+                       break;
                case CDCLK_FREQ_675_617:
-                       return 675000;
+                       freq = 675000;
+                       break;
                default:
                        WARN(1, "Unknown cd freq selection\n");
+                       return -EINVAL;
                }
        }
 
-       /* error case, do as if DPLL0 isn't enabled */
-       return 24000;
+verify:
+       /*
+        * Noticed in some instances that the freq selection is correct but
+        * decimal part is programmed wrong from BIOS where pre-os does not
+        * enable display. Verify the same as well.
+        */
+       if (cdctl == ((cdctl & CDCLK_FREQ_SEL_MASK) | skl_cdclk_decimal(freq)))
+               return freq;
+       else
+               return -EINVAL;
 }
 
 static int broxton_get_display_clock_speed(struct drm_device *dev)
-- 
2.4.3

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