[Intel-gfx] [PATCH] drm/i915/dp: Fix alt mode handling.

[Maarten Lankhorst]

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

Add a intel_edp_choose_mode helper that picks the mode.

If there is no alt mode, it always picks the default mode.
If the alt mode is identical to the default mode, it picks the mode
based on what mode is closest to the request clock.
If the alt mode differs, it only picks the alt mode on exact match.

Testcase: kms_panel_fitting.atomic-fastset
Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Fixes: dc911f5bd8aa ("drm/i915/edp: Allow alternate fixed mode for eDP if available.")
Cc: David Weinehall <david.weinehall at linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni at intel.com>
Cc: Jani Nikula <jani.nikula at intel.com>
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Jim Bride <jim.bride at linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Cc: <stable at vger.kernel.org> # v4.14+
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105469
References: https://bugs.freedesktop.org/show_bug.cgi?id=105456
---
 drivers/gpu/drm/i915/intel_dp.c | 39 +++++++++++++++++++++------------------
 1 file changed, 21 insertions(+), 18 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 9a4a51e79fa1..075981842a7f 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1671,21 +1671,25 @@ static int intel_dp_compute_bpp(struct intel_dp *intel_dp,
 	return bpp;
 }
 
-static bool intel_edp_compare_alt_mode(struct drm_display_mode *m1,
-				       struct drm_display_mode *m2)
+static const struct drm_display_mode *
+intel_edp_choose_mode(const struct drm_display_mode *req,
+		      const struct drm_display_mode *def,
+		      const struct drm_display_mode *alt)
 {
-	bool bres = false;
+	if (!alt)
+		return def;
 
-	if (m1 && m2)
-		bres = (m1->hdisplay == m2->hdisplay &&
-			m1->hsync_start == m2->hsync_start &&
-			m1->hsync_end == m2->hsync_end &&
-			m1->htotal == m2->htotal &&
-			m1->vdisplay == m2->vdisplay &&
-			m1->vsync_start == m2->vsync_start &&
-			m1->vsync_end == m2->vsync_end &&
-			m1->vtotal == m2->vtotal);
-	return bres;
+	if (drm_mode_equal_no_clocks(def, alt)) {
+		int clock;
+
+		if (!drm_mode_equal_no_clocks(req, def))
+			return def;
+
+		clock = def->clock / 2 + alt->clock / 2;
+
+		return req->clock > clock ? def : alt;
+	} else
+		return drm_mode_equal_no_clocks(req, alt) ? alt : def;
 }
 
 bool
@@ -1734,12 +1738,11 @@ intel_dp_compute_config(struct intel_encoder *encoder,
 		pipe_config->has_audio = intel_conn_state->force_audio == HDMI_AUDIO_ON;
 
 	if (intel_dp_is_edp(intel_dp) && intel_connector->panel.fixed_mode) {
-		struct drm_display_mode *panel_mode =
-			intel_connector->panel.alt_fixed_mode;
-		struct drm_display_mode *req_mode = &pipe_config->base.mode;
+		const struct drm_display_mode *panel_mode;
 
-		if (!intel_edp_compare_alt_mode(req_mode, panel_mode))
-			panel_mode = intel_connector->panel.fixed_mode;
+		panel_mode = intel_edp_choose_mode(&pipe_config->base.mode,
+						   intel_connector->panel.fixed_mode,
+						   intel_connector->panel.alt_fixed_mode);
 
 		drm_mode_debug_printmodeline(panel_mode);
 
-- 
2.16.2