drm/i915/tgl: Fix dkl link training

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.

v4:
Using the same is_dp check as ICL, need testing on HDMI over tc port

Issue reported on BSpec 49204.

Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190926210659.56317-3-jose.souza@intel.com

diff --git a/drivers/gpu/drm/i915/display/intel_dpll_mgr.c b/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
index 69abafa45ce9210d76ce8b4b3a2ef3f017d718c2..be69a2344294088d6785edd21b519ffe85995a5c 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
+++ b/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
@@ -2630,13 +2630,13 @@ static bool icl_mg_pll_find_divisors(int clock_khz, bool is_dp, bool use_ssc,
                                continue;
 
                        if (div2 >= 2) {
-                               if (is_dkl) {
-                                       a_divratio = 5;
-                                       tlinedrv = 1;
-                               } else {
-                                       a_divratio = is_dp ? 10 : 5;
-                                       tlinedrv = 2;
-                               }
+                               /*
+                                * Note: a_divratio not matching TGL BSpec
+                                * algorithm but matching hardcoded values and
+                                * working on HW for DP alt-mode at least
+                                */
+                               a_divratio = is_dp ? 10 : 5;
+                               tlinedrv = is_dkl ? 1 : 2;
                        } else {
                                a_divratio = 5;
                                tlinedrv = 0;