bxt_calc_pll_link() has been returning 0 all this while.
This patch adds calculation in bxt_calc_pll_link() based on the chv calculation
used in bxt_find_best_dpll().

Signed-off-by: Vandana Kannan <vandana.kan...@intel.com>
---
 drivers/gpu/drm/i915/i915_reg.h  |  2 ++
 drivers/gpu/drm/i915/intel_ddi.c | 38 ++++++++++++++++++++++++++++++++++++--
 2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index ac985c5..1d9c5dd 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -1171,8 +1171,10 @@ enum skl_disp_power_wells {
 #define _PORT_PLL_EBB_0_B              0x6C034
 #define _PORT_PLL_EBB_0_C              0x6C340
 #define   PORT_PLL_P1_MASK             (0x07 << 13)
+#define   PORT_PLL_P1_SHIFT            13
 #define   PORT_PLL_P1(x)               ((x)  << 13)
 #define   PORT_PLL_P2_MASK             (0x1f << 8)
+#define   PORT_PLL_P2_SHIFT            8
 #define   PORT_PLL_P2(x)               ((x)  << 8)
 #define BXT_PORT_PLL_EBB_0(port)       _PORT3(port, _PORT_PLL_EBB_0_A, \
                                                _PORT_PLL_EBB_0_B,      \
diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
index 42c1487..a8fbcc6 100644
--- a/drivers/gpu/drm/i915/intel_ddi.c
+++ b/drivers/gpu/drm/i915/intel_ddi.c
@@ -968,8 +968,42 @@ static void hsw_ddi_clock_get(struct intel_encoder 
*encoder,
 static int bxt_calc_pll_link(struct drm_i915_private *dev_priv,
                                enum intel_dpll_id dpll)
 {
-       /* FIXME formula not available in bspec */
-       return 0;
+       enum port port = (enum port)dpll;       /* 1:1 port->PLL mapping */
+       uint32_t ebb0, pll0, pll2;
+       uint32_t m2_int, m2_frac;
+       intel_clock_t clock;
+       int refclk = 100000;
+
+       /*
+        * FIXME:
+        * The below calculation needs to be revisited if/when
+        * the calculation in bxt_find_best_dpll() changes.
+        */
+       clock.n = 1;
+       clock.m1 = 2;
+
+       ebb0 = I915_READ(BXT_PORT_PLL_EBB_0(port));
+       clock.p1 = (ebb0 & PORT_PLL_P1_MASK) >> PORT_PLL_P1_SHIFT;
+       clock.p2 = (ebb0 & PORT_PLL_P2_MASK) >> PORT_PLL_P2_SHIFT;
+
+       pll0 = I915_READ(BXT_PORT_PLL(port, 0));
+       m2_int = (pll0 & PORT_PLL_M2_MASK) << 22;
+
+       pll2 = I915_READ(BXT_PORT_PLL(port, 2));
+       m2_frac = (pll2 & PORT_PLL_M2_FRAC_MASK);
+
+       clock.m2 = m2_int | m2_frac;
+
+       clock.m = clock.m1 * clock.m2;
+       clock.p = clock.p1 * clock.p2;
+       if (WARN_ON(clock.n == 0 || clock.p == 0))
+               return 0;
+
+       clock.vco = DIV_ROUND_CLOSEST_ULL((uint64_t)refclk * clock.m,
+                       clock.n << 22);
+       clock.dot = DIV_ROUND_CLOSEST(clock.vco, clock.p);
+
+       return (clock.dot / 5);
 }
 
 static void bxt_ddi_clock_get(struct intel_encoder *encoder,
-- 
2.0.1

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