[Intel-gfx] [PATCH v3 7/9] drm/i915/tgl: Fix dkl link training

[José Roberto de Souza]

Link training is failling when running link at 2.7GHz and 1.62GHz and
following BSpec pll algorithm.

Comparing the values calculated and the ones from the reference table
it looks like MG_CLKTOP2_CORECLKCTL1_A_DIVRATIO should not always set
to 5. For DP ports ICL mg pll algorithm sets it to 10 or 5 based on
div2 value, that matches with dkl hardcoded table.

So implementing this way as it proved to work in HW and leaving a
comment so we know why it do not match BSpec.

Issue reported on BSpec 49204.

Signed-off-by: José Roberto de Souza <jose.souza at intel.com>
---
 drivers/gpu/drm/i915/display/intel_dpll_mgr.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dpll_mgr.c b/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
index 496df4095a21..3c881d4cf973 100644
--- a/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
+++ b/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
@@ -2631,7 +2631,12 @@ static bool icl_mg_pll_find_divisors(int clock_khz, bool is_dp, bool use_ssc,
 
 			if (div2 >= 2) {
 				if (is_dkl) {
-					a_divratio = 5;
+					/*
+					 * Note: a_divratio not matching TGL
+					 * BSpec algorithm but matching
+					 * hardcoded values and working on HW
+					 */
+					a_divratio = 10;
 					tlinedrv = 1;
 				} else {
 					a_divratio = is_dp ? 10 : 5;
-- 
2.23.0