RE: [PATCH v1] drm/i915/display: Add command line param for DC balance

[Golani, Mitulkumar Ajitkumar]

> -----Original Message-----
> From: Jani Nikula <jani.nik...@linux.intel.com>
> Sent: 04 September 2026 13:59
> To: Golani, Mitulkumar Ajitkumar <mitulkumar.ajitkumar.gol...@intel.com>;
> intel-gfx@lists.freedesktop.org
> Cc: intel...@lists.freedesktop.org; Nautiyal, Ankit K
> <ankit.k.nauti...@intel.com>
> Subject: Re: [PATCH v1] drm/i915/display: Add command line param for DC
> balance
> 
> On Fri, 28 Aug 2026, Mitul Golani <mitulkumar.ajitkumar.gol...@intel.com>
> wrote:
> > Add a new module parameter 'enable_dc_balance' to allow enabling or
> > disabling the VRR DC balance feature at runtime. The DC balance
> > computation in intel_vrr_dc_balance_compute_config() now honours this
> > parameter, so the feature can be toggled without recompiling.
> 
> Why? Everything in the commit message above is obvious, and can be trivially
> deduced from the code changes, but I'm none the wiser why this change is
> needed.
> 
> Also, what's the specific need for this to be a module parameter? No new
> module parameters should be added without strong justification. Could this
> be a debugfs knob instead?
> 
> Module parameters are, as the name suggests, per module, not per device.
> 
> 
> BR,
> Jani.

Hello Jani,
 
We have observed timing-related issues with DC balance on some panel/TCON
combinations and are working with the DMC firmware team on a fix. We are also 
identifying affected TCONs for appropriate quirks.
 
Until this analysis is complete, we want to keep DC balance disabled by default 
to 
preserve existing VRR behavior. The module parameter provides a boot-time 
opt-in 
for configurations where it is needed.
 
I believe a module parameter is preferable to debugfs since this decision may 
need 
to be made from the initial display configuration rather than as a runtime 
debug control.

Thanks,
Mitul
> 
> >
> > Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.gol...@intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_display_params.c | 3 +++
> > drivers/gpu/drm/i915/display/intel_display_params.h | 1 +
> >  drivers/gpu/drm/i915/display/intel_vrr.c            | 4 +++-
> >  3 files changed, 7 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 2aed110c5b09..ed3aa84c5d43 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display_params.c
> > +++ b/drivers/gpu/drm/i915/display/intel_display_params.c
> > @@ -120,6 +120,9 @@ 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, int, 0400,
> > +   "Enable DC Balance (0=disabled, 1=enable). Default: 1 (use per-chip
> > +default)");
> > +
> >  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 b95ecf728daa..8c28c27e2c46 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(int, 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 e36db1174440..1698c54e258b 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;
> 
> --
> Jani Nikula, Intel