Quoting Maarten Lankhorst (2018-03-13 09:28:55)
> On fi-cnl-y3 we have 2 modes that differ only by crtc_clock. This means
> that if we request the normal mode, we automatically get the downclocked
> mode.
>
> This can be seen during boot:
> [drm:drm_helper_probe_single_connector_modes] [CONNECTOR:101:eDP-1] probed modes :
> [drm:drm_mode_debug_printmodeline] Modeline 102:"3840x2160" 60 533250 3840 3888 3920 4000 2160 2163 2168 2222 0x48 0xa
> [drm:drm_mode_debug_printmodeline] Modeline 103:"3840x2160" 48 426600 3840 3888 3920 4000 2160 2163 2168 2222 0x40 0xa
> ...
> [drm:intel_dump_pipe_config [i915]] [CRTC:51:pipe A][modeset]
> [drm:intel_dump_pipe_config [i915]] output_types: EDP (0x100)
> [drm:intel_dump_pipe_config [i915]] cpu_transcoder: EDP, pipe bpp: 24, dithering: 0
> [drm:intel_dump_pipe_config [i915]] dp m_n: lanes: 4; gmch_m: 4970250, gmch_n: 8388608, link_m: 828375, link_n: 1048576, tu: 64
> [drm:intel_dump_pipe_config [i915]] dp m2_n2: lanes: 4; gmch_m: 4970250, gmch_n: 8388608, link_m: 828375, link_n: 1048576, tu: 64
> [drm:intel_dump_pipe_config [i915]] audio: 0, infoframes: 0
> [drm:intel_dump_pipe_config [i915]] requested mode:
> [drm:drm_mode_debug_printmodeline] Modeline 0:"3840x2160" 60 533250 3840 3888 3920 4000 2160 2163 2168 2222 0x48 0xa
> [drm:intel_dump_pipe_config [i915]] adjusted mode:
> [drm:drm_mode_debug_printmodeline] Modeline 0:"3840x2160" 48 426600 3840 3888 3920 4000 2160 2163 2168 2222 0x40 0xa
>
> Testcase: kms_panel_fitting.atomic-fastset
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> Fixes: dc911f5bd8aa ("drm/i915/edp: Allow alternate fixed mode for eDP if available.")
> Cc: David Weinehall <david.weinehall@xxxxxxxxxxxxxxx>
> Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
> Cc: Paulo Zanoni <paulo.r.zanoni@xxxxxxxxx>
> Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Jim Bride <jim.bride@xxxxxxxxxxxxxxx>
> Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.14+
> ---
> drivers/gpu/drm/i915/intel_dp.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 9a4a51e79fa1..0bd3cc1c82b4 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -1684,7 +1684,8 @@ static bool intel_edp_compare_alt_mode(struct drm_display_mode *m1,
> m1->vdisplay == m2->vdisplay &&
> m1->vsync_start == m2->vsync_start &&
> m1->vsync_end == m2->vsync_end &&
> - m1->vtotal == m2->vtotal);
> + m1->vtotal == m2->vtotal &&
> + m1->clock == m2->clock);
Should it be exact on clock or just closer to alt-clock than
preferred-clock?
-Chris