[Intel-gfx] [PATCH 1/5] drm/i915/skl: Work around incorrect BIOS WRPLL PDIV programming

[Imre Deak]

The BIOS of at least one ASUS-Z170M system with an SKL I have programs
the 101b WRPLL PDIV divider value, which is the encoding for PDIV=7 with
bit#0 incorrectly set.

This happens with the

"3840x2160": 30 262750 3840 3888 3920 4000 2160 2163 2168 2191 0x48 0x9

HDMI mode (scaled from a 1024x768 src fb) set by BIOS and the

ref_clock=24000, dco_integer=383, dco_fraction=5802, pdiv=7, qdiv=1, kdiv=1

WRPLL parameters (assuming PDIV=7 was the intended setting). This
corresponds to 262749 PLL frequency/port clock.

Later the driver sets the same mode for which it calculates the same
dco_int/dco_frac/div WRPLL parameters (with the correct PDIV=7 encoding).

Based on the above, let's assume that PDIV=7 was intended and the HW
just ignores bit#0 in the PDIV register field for this setting, treating
100b and 101b encodings the same way.

Signed-off-by: Imre Deak <imre.deak at intel.com>
---
 drivers/gpu/drm/i915/display/intel_dpll_mgr.c | 8 ++++++++
 drivers/gpu/drm/i915/i915_reg.h               | 1 +
 2 files changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_dpll_mgr.c b/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
index e08684e34078..095b53fe3a21 100644
--- a/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
+++ b/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
@@ -1602,6 +1602,14 @@ static int skl_ddi_wrpll_get_freq(struct drm_i915_private *i915,
 	case DPLL_CFGCR2_PDIV_3:
 		p0 = 3;
 		break;
+	case DPLL_CFGCR2_PDIV_7 | (1 << DPLL_CFGCR2_PDIV_SHIFT):
+		/*
+		 * Incorrect ASUS-Z170M BIOS setting, the HW seems to ignore bit#0,
+		 * handling it the same way as PDIV_7.
+		 */
+		drm_err(&i915->drm, "Invalid WRPLL PDIV divider value, fixing it.\n");
+		p0 = 7;
+		break;
 	case DPLL_CFGCR2_PDIV_7:
 		p0 = 7;
 		break;
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 47730a176698..f70e45bd3810 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -10253,6 +10253,7 @@ enum skl_power_gate {
 #define  DPLL_CFGCR2_KDIV_3 (2 << 5)
 #define  DPLL_CFGCR2_KDIV_1 (3 << 5)
 #define  DPLL_CFGCR2_PDIV_MASK		(7 << 2)
+#define  DPLL_CFGCR2_PDIV_SHIFT		2
 #define  DPLL_CFGCR2_PDIV(x)		((x) << 2)
 #define  DPLL_CFGCR2_PDIV_1 (0 << 2)
 #define  DPLL_CFGCR2_PDIV_2 (1 << 2)
-- 
2.25.1