RE: [PATCH 12/12] drm/i915/vrr: Fix seamless_mn drrs for PTL

[Golani, Mitulkumar Ajitkumar]

> -----Original Message-----
> From: Intel-gfx <intel-gfx-boun...@lists.freedesktop.org> On Behalf Of Ankit
> Nautiyal
> Sent: 20 August 2025 13:35
> To: intel-gfx@lists.freedesktop.org; intel...@lists.freedesktop.org
> Cc: ville.syrj...@linux.intel.com; Nautiyal, Ankit K
> <ankit.k.nauti...@intel.com>
> Subject: [PATCH 12/12] drm/i915/vrr: Fix seamless_mn drrs for PTL
> 
> With VRR timing generator always on, the fixed refresh rate is achieved by
> setting vrr.flipline and vrr.vmax as the vtotal for the desired mode.
> 
> This creates a problem for seamless_mn drrs feature, where user can
> seamlessly set a lower mode on the supporting panels. With VRR timing
> generator, the vrr.flipline and vrr.vmax are set to vtotal, but that 
> corresponds
> to the higher mode.
> 
> To fix this, re-compute the vrr timings when seamless_mn drrs is in picture. 
> At
> the same time make sure that the vrr.guardband is set as per the highest mode
> for such panels, so that switching between higher to lower mode, does not
> change the vrr.guardband.
> 
> v2: Add a new member `use_highest_mode` to vrr struct to help set the vrr
> timings for highest mode for the seamless_mn drrs case.
> v3:
> -Modify existing function to compute fixed refresh rate timings instead of
> adding a new function. (Mitul) -Tweak computation for scaling the vtotal and
> use DIV_ROUND_UP_ULL.
> -Improve documentation.
> 
> Signed-off-by: Ankit Nautiyal <ankit.k.nauti...@intel.com>
> ---
>  .../drm/i915/display/intel_display_types.h    |  2 +
>  drivers/gpu/drm/i915/display/intel_dp.c       |  2 +-
>  drivers/gpu/drm/i915/display/intel_dp.h       |  1 +
>  drivers/gpu/drm/i915/display/intel_vrr.c      | 90 ++++++++++++++++++-
>  4 files changed, 90 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h
> b/drivers/gpu/drm/i915/display/intel_display_types.h
> index 0d945d1fedd6..0eb5bbd753b5 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> @@ -1318,6 +1318,8 @@ struct intel_crtc_state {
>               u8 pipeline_full;
>               u16 flipline, vmin, vmax, guardband;
>               u32 vsync_end, vsync_start;
> +             /* Indicates VRR timing is scaled to highest mode for seamless
> M/N */
> +             bool use_highest_mode;
>       } vrr;
> 
>       /* Content Match Refresh Rate state */ diff --git
> a/drivers/gpu/drm/i915/display/intel_dp.c
> b/drivers/gpu/drm/i915/display/intel_dp.c
> index 4c3a4b7c0abe..17a58f439954 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -1741,7 +1741,7 @@ static int intel_dp_max_bpp(struct intel_dp
> *intel_dp,
>       return bpp;
>  }
> 
> -static bool has_seamless_m_n(struct intel_connector *connector)
> +bool has_seamless_m_n(struct intel_connector *connector)
>  {
>       struct intel_display *display = to_intel_display(connector);
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.h
> b/drivers/gpu/drm/i915/display/intel_dp.h
> index bfd1bd448672..932f5504399e 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.h
> +++ b/drivers/gpu/drm/i915/display/intel_dp.h
> @@ -216,5 +216,6 @@ int intel_dp_dsc_bpp_step_x16(const struct
> intel_connector *connector);  void intel_dp_dpcd_set_probe(struct intel_dp
> *intel_dp, bool force_on_external);  bool intel_dp_in_hdr_mode(const struct
> drm_connector_state *conn_state);  int intel_dp_compute_sdp_latency(struct
> intel_crtc_state *crtc_state, bool assume_all_enabled);
> +bool has_seamless_m_n(struct intel_connector *connector);
> 
>  #endif /* __INTEL_DP_H__ */
> diff --git a/drivers/gpu/drm/i915/display/intel_vrr.c
> b/drivers/gpu/drm/i915/display/intel_vrr.c
> index 170f7bcdb8a8..2cae20a99399 100644
> --- a/drivers/gpu/drm/i915/display/intel_vrr.c
> +++ b/drivers/gpu/drm/i915/display/intel_vrr.c
> @@ -11,6 +11,7 @@
>  #include "intel_display_regs.h"
>  #include "intel_display_types.h"
>  #include "intel_dp.h"
> +#include "intel_panel.h"
>  #include "intel_vrr.h"
>  #include "intel_vrr_regs.h"
>  #include "skl_scaler.h"
> @@ -299,6 +300,16 @@ void intel_vrr_set_fixed_rr_timings(const struct
> intel_crtc_state *crtc_state)
>       if (!intel_vrr_possible(crtc_state))
>               return;
> 
> +     if (crtc_state->vrr.use_highest_mode) {
> +             intel_de_write(display, TRANS_VRR_VMIN(display,
> cpu_transcoder),
> +                            crtc_state->vrr.vmin - 1);
> +             intel_de_write(display, TRANS_VRR_VMAX(display,
> cpu_transcoder),
> +                            crtc_state->vrr.vmax - 1);
> +             intel_de_write(display, TRANS_VRR_FLIPLINE(display,
> cpu_transcoder),
> +                            crtc_state->vrr.flipline - 1);
> +             return;
> +     }
> +
>       intel_de_write(display, TRANS_VRR_VMIN(display, cpu_transcoder),
>                      intel_vrr_fixed_rr_vmin(crtc_state) - 1);
>       intel_de_write(display, TRANS_VRR_VMAX(display, cpu_transcoder),
> @@ -307,15 +318,69 @@ void intel_vrr_set_fixed_rr_timings(const struct
> intel_crtc_state *crtc_state)
>                      intel_vrr_fixed_rr_flipline(crtc_state) - 1);  }
> 
> +static bool needs_seamless_m_n_timings(struct intel_crtc_state *crtc_state,
> +                                    struct intel_connector *connector) {
> +     if (!has_seamless_m_n(connector) || crtc_state->joiner_pipes)
> +             return false;
> +
> +     return true;
> +}
> +
> +static int intel_vrr_scale_vtotal_for_seamless_m_n(struct intel_crtc_state
> *crtc_state,
> +                                                struct intel_connector
> *connector) {
> +     const struct drm_display_mode *highest_mode =
> intel_panel_highest_mode(connector);
> +     const struct drm_display_mode *adjusted_mode = &crtc_state-
> >hw.adjusted_mode;
> +     int vtotal = adjusted_mode->crtc_vtotal;
> +
> +     /*
> +      * For panels with seamless_m_n drrs, the user can seamlessly switch
> to
> +      * a lower mode, which has a lower clock. This works with legacy
> timing
> +      * generator, but not with the VRR timing generator.
> +      *
> +      * The VRR timing generator requires flipline and vmax to be equal for
> +      * fixed refresh rate operation. The default fixed RR computation sets
> +      * these to the current mode's vtotal. However, when switching to a
> +      * lower clock mode, this would result in a higher refresh rate than
> +      * desired.
> +      *
> +      * To simulate the lower refresh rate correctly, we scale the vtotal
> +      * based on the ratio of the highest mode's clock to the current mode's
> +      * clock.
> +      *
> +      * When switching to a higher clock mode, the current vtotal already
> +      * results in the desired refresh rate, so no scaling is needed.
> +      *
> +      * So compute the scaled vtotal if required, and update vrr.vmin to
> +      * the scaled value. Also, set vrr.use_highest_mode to indicate that
> +      * VRR timings are based on the highest mode.
> +      */
> +     if (highest_mode && adjusted_mode->crtc_clock < highest_mode-
> >clock) {
> +             vtotal = DIV_ROUND_UP_ULL(vtotal * highest_mode->clock,
> +                                       adjusted_mode->crtc_clock);
> +             crtc_state->vrr.vmin = vtotal;
> +             crtc_state->vrr.use_highest_mode = true;
> +     }
> +
> +     return vtotal;
> +}
> +
>  static
> -void intel_vrr_compute_fixed_rr_timings(struct intel_crtc_state *crtc_state)
> +void intel_vrr_compute_fixed_rr_timings(struct intel_crtc_state *crtc_state,
> +                                     struct intel_connector *connector)
>  {
> +     int vtotal = crtc_state->hw.adjusted_mode.crtc_vtotal;
> +
> +     if (needs_seamless_m_n_timings(crtc_state, connector))
> +             vtotal = intel_vrr_scale_vtotal_for_seamless_m_n(crtc_state,
> +connector);
> +
>       /*
>        * For fixed rr,  vmin = vmax = flipline.
>        * vmin is already set to crtc_vtotal set vmax and flipline the same.
>        */
> -     crtc_state->vrr.vmax = crtc_state->hw.adjusted_mode.crtc_vtotal;
> -     crtc_state->vrr.flipline = crtc_state->hw.adjusted_mode.crtc_vtotal;
> +     crtc_state->vrr.vmax = vtotal;
> +     crtc_state->vrr.flipline = vtotal;
>  }
> 
>  static
> @@ -397,7 +462,7 @@ intel_vrr_compute_config(struct intel_crtc_state
> *crtc_state,
>       else if (is_cmrr_frac_required(crtc_state) && is_edp)
>               intel_vrr_compute_cmrr_timings(crtc_state);
>       else
> -             intel_vrr_compute_fixed_rr_timings(crtc_state);
> +             intel_vrr_compute_fixed_rr_timings(crtc_state, connector);
> 
>       /*
>        * flipline determines the min vblank length the hardware will @@ -
> 478,6 +543,7 @@ int intel_vrr_compute_guardband(struct intel_crtc_state
> *crtc_state,  {
>       const struct drm_display_mode *adjusted_mode = &crtc_state-
> >hw.adjusted_mode;
>       struct intel_display *display = to_intel_display(crtc_state);
> +     const struct drm_display_mode *highest_mode;
>       int dsc_prefill_time = 0;
>       int psr2_pr_latency = 0;
>       int scaler_prefill_time;
> @@ -490,6 +556,22 @@ int intel_vrr_compute_guardband(struct
> intel_crtc_state *crtc_state,
>       int guardband;
>       int pm_delay;
> 
> +     /*
> +      * For seamless m_n the clock is changed while other modeline
> +      * parameters are same. In that case the linetime_us will change,
> +      * causing the guardband to change, and the seamless switch to
> +      * lower mode would not take place.
> +      * To avoid this, take the highest mode where panel supports
> +      * seamless drrs and make guardband equal to the vblank length
> +      * for the highest mode.
> +      */
> +     highest_mode = intel_panel_highest_mode(connector);
> +     if (needs_seamless_m_n_timings(crtc_state, connector) &&
> highest_mode) {
> +             guardband = highest_mode->vtotal - highest_mode->vdisplay;
> +
> +             return guardband;
> +     }
> +

Reviewed-by: Mitul Golani <mitulkumar.ajitkumar.gol...@intel.com>

>       linetime_us = DIV_ROUND_UP(adjusted_mode->crtc_htotal * 1000,
>                                  adjusted_mode->crtc_clock);
> 
> --
> 2.45.2