drm/i915: Read timings from the correct transcoder in intel_crtc_mode_get()

intel_crtc->config->cpu_transcoder isn't yet filled out when
intel_crtc_mode_get() gets called during output probing, so we should
not use it there. Instead intel_crtc_mode_get() figures out the correct
transcoder on its own, and that's what we should use.

If the BIOS boots LVDS on pipe B, intel_crtc_mode_get() would actually
end up reading the timings from pipe A instead (since PIPE_A==0),
which clearly isn't what we want.

It looks to me like this may have been broken by
commit eccb140b ("drm/i915: hw state readout&check support for cpu_transcoder")
as that one removed the early initialization of cpu_transcoder from
intel_crtc_init().

Cc: stable@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: Rob Kramer <rob@solution-space.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reported-by: Rob Kramer <rob@solution-space.com>
Fixes: eccb140b ("drm/i915: hw state readout&check support for cpu_transcoder")
References: https://lists.freedesktop.org/archives/dri-devel/2016-April/104142.htmlSigned-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/1459525046-19425-1-git-send-email-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/intel_display.c

@@ -10253,13 +10253,10 @@ struct drm_display_mode *intel_crtc_mode_get(struct drm_device *dev,
 {
 	struct drm_i915_private *dev_priv = to_i915(dev);
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
-	enum transcoder cpu_transcoder = intel_crtc->config->cpu_transcoder;
+	enum transcoder cpu_transcoder;
 	struct drm_display_mode *mode;
 	struct intel_crtc_state *pipe_config;
-	int htot = I915_READ(HTOTAL(cpu_transcoder));
-	int hsync = I915_READ(HSYNC(cpu_transcoder));
-	int vtot = I915_READ(VTOTAL(cpu_transcoder));
-	int vsync = I915_READ(VSYNC(cpu_transcoder));
+	u32 htot, hsync, vtot, vsync;
 	enum pipe pipe = intel_crtc->pipe;
 
 	mode = kzalloc(sizeof(*mode), GFP_KERNEL);
@@ -10287,6 +10284,13 @@ struct drm_display_mode *intel_crtc_mode_get(struct drm_device *dev,
 	i9xx_crtc_clock_get(intel_crtc, pipe_config);
 
 	mode->clock = pipe_config->port_clock / pipe_config->pixel_multiplier;
+
+	cpu_transcoder = pipe_config->cpu_transcoder;
+	htot = I915_READ(HTOTAL(cpu_transcoder));
+	hsync = I915_READ(HSYNC(cpu_transcoder));
+	vtot = I915_READ(VTOTAL(cpu_transcoder));
+	vsync = I915_READ(VSYNC(cpu_transcoder));
+
 	mode->hdisplay = (htot & 0xffff) + 1;
 	mode->htotal = ((htot & 0xffff0000) >> 16) + 1;
 	mode->hsync_start = (hsync & 0xffff) + 1;