Re: [PATCH 0/6] drm/i915/intel_panel: Fix seamless VRR mode switching for DRRS panels

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, May 22, 2026 at 06:55:05PM +0530, Ankit Nautiyal wrote:
> Currently intel_panel_fixed_mode() can return a lower refresh rate mode
> for VRR panels if the lower refresh rate mode is first in the list.
> This creates problems for seamless switch features like LRR and
> Seamless-DRRS, as it results in changes to vsync_start/end causing a
> full modeset instead of a seamless switch.
> 
> This is particularly problematic for DRRS panels on platforms without
> double buffered M/N support for LNL+ (display version 20+), where
> seamless clock changes are not possible.
> 
> This series attempts to fix this by:
> 1. Adding a helper to get the highest refresh rate mode from the list of
>    fixed modes for a connector.
> 2. When a seamless switch to a lower mode is desired, making
>    intel_panel_fixed_mode() return the highest refresh rate mode,
>    provided the requested rate is in VRR range. The vblank is then
>    extended to provide the desired refresh rate.
> 
> To determine whether a full modeset or seamless switch is intended, the
> connector state is checked for the allow_modeset flag. A nullable
> conn_state parameter is added to intel_panel_fixed_mode() and
> intel_panel_compute_config() for this purpose.
> 
> Rev2:
>  - Address Ville's comments to preserve Vtotal-Vsync distance while
>    adjusting VTOTAL.
>  - Address Manasi's comments to always go with highest RR mode
>    irrespective of allow_modeset flag for modes that have same clock but
>    different votal.
> 
> Rev3:
>  - Drop patch to deprecate TRANS_VSYNC, instead add Vsync start/end in
>    lrr codepaths. (Ville).
>  - Fix the condition to avoid picking higher RR mode for DRRS panels
>    when allow modeset flag is set.
> 
> Ankit Nautiyal (6):
>   drm/i915/display: Handle VSYNC timing in LRR path
>   drm/i915/panel: Preserve Vtotal-Vsync distance while adjusting vtotal
>   drm/i915/intel_panel: Add a helper to get the highest refresh rate
>     mode
>   drm/i915/intel_panel: Pass crtc_state to intel_panel_compute_config
>   drm/i915/intel_panel: Use highest refresh rate mode for VRR panels
>   drm/i915/intel_panel: Refine VRR fixed mode selection for DRRS panels

I didn't really go through the rest of the stuff in fine detail,
but my initial reaction was that it all feels complicated.

Here's a quick attempt at a simpler thing:
 https://github.com/vsyrjala/linux.git vrr_no_allow_modeset

Ie. just try to make sure the fixed mode selected by a
!allow_modeset commit is "VRR compatible" with the old
adjusted_mode. This is completely untested though, so not
sure it actually works.

The guardband does still pose a bit of a problem in that
the optimized guardband might exceed the available vblank
for either the old or new mode, in case we can end up with
a change in guardband. If that turns out to be a serious issue
then I suppose we might also need to preserve the current
guardband value instead of recalculating it...

> 
>  drivers/gpu/drm/i915/display/icl_dsi.c       |   2 +-
>  drivers/gpu/drm/i915/display/intel_display.c |   9 +-
>  drivers/gpu/drm/i915/display/intel_dp.c      |   2 +-
>  drivers/gpu/drm/i915/display/intel_dvo.c     |   2 +-
>  drivers/gpu/drm/i915/display/intel_lvds.c    |   2 +-
>  drivers/gpu/drm/i915/display/intel_panel.c   | 102 +++++++++++++++----
>  drivers/gpu/drm/i915/display/intel_panel.h   |   9 +-
>  drivers/gpu/drm/i915/display/intel_sdvo.c    |   8 +-
>  drivers/gpu/drm/i915/display/vlv_dsi.c       |   2 +-
>  9 files changed, 108 insertions(+), 30 deletions(-)
> 
> -- 
> 2.45.2

-- 
Ville Syrjälä
Intel