[PATCH v3] drm/i915/vrr: Disable DC balance by default

[Mitul Golani <mitulkumar.ajitkumar.golani@intel.com>]

Disable VRR DC balance by default due to timing issues observed on some
panel/TCON combinations.

Keep the module parameter to enable DC balance during debugging and to
isolate DC balance effects from underlying VRR/display timing issues.

--v2:
- Make enable_dc_balance a bool and keep it disabled by default; fix the
  parameter type/value mismatch and correct the description (Chaitanya
  Kumar Borah, Jani Nikula)
- Explain in the commit message why the feature is gated and why a
  module parameter is used (Jani Nikula)

--v3:
- Commit message update (Jani Nikula)

Fixes: 555819270707 ("drm/i915/vrr: Enable DC Balance")
Cc: <stable@vger.kernel.org> # v7.0+
Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.golani@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
---
 drivers/gpu/drm/i915/display/intel_display_params.c | 4 ++++
 drivers/gpu/drm/i915/display/intel_display_params.h | 1 +
 drivers/gpu/drm/i915/display/intel_vrr.c            | 4 +++-
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_display_params.c b/drivers/gpu/drm/i915/display/intel_display_params.c
index 2aed110c5b090..ca0ef466bb103 100644
--- a/drivers/gpu/drm/i915/display/intel_display_params.c
+++ b/drivers/gpu/drm/i915/display/intel_display_params.c
@@ -120,6 +120,10 @@ intel_display_param_named_unsafe(enable_psr, int, 0400,
 	"(0=disabled, 1=enable up to PSR1, 2=enable up to PSR2) "
 	"Default: -1 (use per-chip default)");
 
+intel_display_param_named_unsafe(enable_dc_balance, bool, 0400,
+	"Enable VRR DC balance (0=disabled, 1=enabled). "
+	"Default: 0 (disabled)");
+
 intel_display_param_named_unsafe(enable_panel_replay, int, 0400,
 	"Enable Panel Replay (0=disabled, 1=enabled). Default: -1 (use per-chip default)");
 
diff --git a/drivers/gpu/drm/i915/display/intel_display_params.h b/drivers/gpu/drm/i915/display/intel_display_params.h
index ba01aeaf89440..5c5a1a1358c32 100644
--- a/drivers/gpu/drm/i915/display/intel_display_params.h
+++ b/drivers/gpu/drm/i915/display/intel_display_params.h
@@ -46,6 +46,7 @@ struct drm_printer;
 	param(bool, enable_dp_mst, true, 0600) \
 	param(int, enable_fbc, -1, 0600) \
 	param(int, enable_psr, -1, 0600) \
+	param(bool, enable_dc_balance, false, 0600) \
 	param(int, enable_panel_replay, -1, 0600) \
 	param(bool, psr_safest_params, false, 0400) \
 	param(bool, enable_psr2_sel_fetch, true, 0400) \
diff --git a/drivers/gpu/drm/i915/display/intel_vrr.c b/drivers/gpu/drm/i915/display/intel_vrr.c
index e36db11744405..1698c54e258b4 100644
--- a/drivers/gpu/drm/i915/display/intel_vrr.c
+++ b/drivers/gpu/drm/i915/display/intel_vrr.c
@@ -439,10 +439,12 @@ static bool intel_vrr_dc_balance_possible(const struct intel_crtc_state *crtc_st
 static void
 intel_vrr_dc_balance_compute_config(struct intel_crtc_state *crtc_state)
 {
+	struct intel_display *display = to_intel_display(crtc_state);
 	int guardband_usec, adjustment_usec;
 	struct drm_display_mode *adjusted_mode = &crtc_state->hw.adjusted_mode;
 
-	if (!intel_vrr_dc_balance_possible(crtc_state) || !crtc_state->vrr.enable)
+	if (!intel_vrr_dc_balance_possible(crtc_state) ||
+	    !crtc_state->vrr.enable || !display->params.enable_dc_balance)
 		return;
 
 	crtc_state->vrr.dc_balance.vmax = crtc_state->vrr.vmax;
-- 
2.48.1