[PATCH 3/4] drm/i915: use current mode if the size matches the preferred mode

[Jesse Barnes]

From: Kristian Høgsberg <hoegsberg at gmail.com>

The BIOS may set a native mode that doesn't quite match the preferred
mode timings.  It should be ok to use however if it uses the same size,
so try to avoid a mode set in that case.

Signed-off-by: Kristian Høgsberg <hoegsberg at gmail.com>
Signed-off-by: Jesse Barnes <jbarnes at virtuousgeek.org>
---
 drivers/gpu/drm/drm_modes.c        |    8 ++++++++
 drivers/gpu/drm/i915/intel_fbdev.c |   37 ++++++++++++++++++------------------
 include/drm/drm_crtc.h             |    2 ++
 3 files changed, 28 insertions(+), 19 deletions(-)

diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
index b073315..7d2dda4 100644
--- a/drivers/gpu/drm/drm_modes.c
+++ b/drivers/gpu/drm/drm_modes.c
@@ -894,6 +894,14 @@ bool drm_mode_equal_no_clocks_no_stereo(const struct drm_display_mode *mode1,
 }
 EXPORT_SYMBOL(drm_mode_equal_no_clocks_no_stereo);
 
+bool drm_mode_same_size(const struct drm_display_mode *mode1,
+			const struct drm_display_mode *mode2)
+{
+	return mode1->vdisplay == mode2->vdisplay &&
+		mode1->hdisplay == mode2->hdisplay;
+}
+EXPORT_SYMBOL(drm_mode_same_size);
+
 /**
  * drm_mode_validate_size - make sure modes adhere to size constraints
  * @dev: DRM device
diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
index d6d78c8..f81e3db 100644
--- a/drivers/gpu/drm/i915/intel_fbdev.c
+++ b/drivers/gpu/drm/i915/intel_fbdev.c
@@ -369,31 +369,30 @@ static bool intel_fb_initial_config(struct drm_fb_helper *fb_helper,
 		/* go for command line mode first */
 		modes[i] = drm_pick_cmdline_mode(fb_conn, width, height);
 
-		/* try for preferred next */
+		/* try for preferred next or match current */
 		if (!modes[i]) {
+			struct drm_display_mode *preferred;
+
 			DRM_DEBUG_KMS("looking for preferred mode on connector %d\n",
 				      fb_conn->connector->base.id);
-			modes[i] = drm_has_preferred_mode(fb_conn, width,
-							  height);
-		}
-
-		/* last resort: use current mode */
-		if (!modes[i]) {
-			/*
-			 * IMPORTANT: We want to use the adjusted mode (i.e.
-			 * after the panel fitter upscaling) as the initial
-			 * config, not the input mode, which is what crtc->mode
-			 * usually contains. But since our current fastboot
-			 * code puts a mode derived from the post-pfit timings
-			 * into crtc->mode this works out correctly. We don't
-			 * use hwmode anywhere right now, so use it for this
-			 * since the fb helper layer wants a pointer to
-			 * something we own.
-			 */
+			preferred = drm_has_preferred_mode(fb_conn, width,
+							   height);
 			intel_mode_from_pipe_config(&encoder->crtc->hwmode,
 						    &to_intel_crtc(encoder->crtc)->config);
-			modes[i] = &encoder->crtc->hwmode;
+ 			modes[i] = &encoder->crtc->hwmode;
+
+			if (preferred &&
+			    !drm_mode_same_size(preferred, modes[i])) {
+				DRM_DEBUG_KMS("using preferred mode %s "
+					      "instead of current mode %s "
+					      "on connector %d\n",
+					      preferred->name,
+					      modes[i]->name,
+					      fb_conn->connector->base.id);
+				modes[i] = preferred;
+			}
 		}
+
 		crtcs[i] = new_crtc;
 
 		DRM_DEBUG_KMS("connector %s on crtc %d: %s\n",
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index f764654..d5ebe3b 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -1020,6 +1020,8 @@ extern bool drm_mode_equal(const struct drm_display_mode *mode1, const struct dr
 extern bool drm_mode_equal_no_clocks_no_stereo(const struct drm_display_mode *mode1, const struct drm_display_mode *mode2);
 extern int drm_mode_width(const struct drm_display_mode *mode);
 extern int drm_mode_height(const struct drm_display_mode *mode);
+extern bool drm_mode_same_size(const struct drm_display_mode *mode1,
+			       const struct drm_display_mode *mode2);
 
 /* for us by fb module */
 extern struct drm_display_mode *drm_mode_create(struct drm_device *dev);
-- 
1.7.9.5