[Intel-gfx] [PATCH] drm/i915/dsi: let HW maintain the HS-TRAIL timing

[William Tseng]

This change is to avoid over-specification of the TEOT timing
parameter, which is derived from software in current design.

Supposed that THS-TRAIL and THS-EXIT have the minimum values,
i.e., 60 and 100 in ns. If SW is overriding the HW default,
the TEOT value becomes 150 ns, approximately calculated by
the following formula.

  DIV_ROUND_UP(60/50)*50 + DIV_ROUND_UP(100/50))*50/2, where 50
  is LP Escape Clock time in ns.

The TEOT value 150 ns is larger than the maximum value,
around 136 ns if UI is 1.8ns, (105 ns + 12*UI, defined by MIPI
DPHY specification).

However, the TEOT value will meet the specification if THS-TRAIL
is set to the HW default, instead of software overriding.

Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
Cc: Jani Nikula <jani.nikula at linux.intel.com>
Cc: Vandita Kulkarni <vandita.kulkarni at intel.com>
Cc: Lee Shawn C <shawn.c.lee at intel.com>
Cc: Cooper Chiou <cooper.chiou at intel.com>
Signed-off-by: William Tseng <william.tseng at intel.com>
---
 drivers/gpu/drm/i915/display/icl_dsi.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/icl_dsi.c b/drivers/gpu/drm/i915/display/icl_dsi.c
index 168c84a74d30..0d22d3ed9734 100644
--- a/drivers/gpu/drm/i915/display/icl_dsi.c
+++ b/drivers/gpu/drm/i915/display/icl_dsi.c
@@ -1957,8 +1957,6 @@ static void icl_dphy_param_init(struct intel_dsi *intel_dsi)
 					 HS_PREPARE(prepare_cnt) |
 					 HS_ZERO_OVERRIDE |
 					 HS_ZERO(hs_zero_cnt) |
-					 HS_TRAIL_OVERRIDE |
-					 HS_TRAIL(trail_cnt) |
 					 HS_EXIT_OVERRIDE |
 					 HS_EXIT(exit_zero_cnt));
 
-- 
2.17.1