drm/i915: detect PCH encoders on Haswell

On Haswell, the recommended PCH-connected output is the one driven by DDI
E in FDI mode, used for VGA connection. All the others are handled by the
CPU.

Note that this does not accounts for Haswell/PPT combination yet, so if we
encounter such combination an error message is thrown to indicate that
things could go wrong.

v2: improve non-LPT detection warning per Daniel Vetter's suggestion.

Signed-off-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 16 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index cc910e69f709..bb049a178632 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -2610,6 +2610,22 @@ static bool intel_crtc_driving_pch(struct drm_crtc *crtc)
                 if (encoder->base.crtc != crtc)
                         continue;
 
+                /* On Haswell, LPT PCH handles the VGA connection via FDI, and Haswell
+                 * CPU handles all others */
+                if (IS_HASWELL(dev)) {
+                        /* It is still unclear how this will work on PPT, so throw up a warning */
+                        WARN_ON(!HAS_PCH_LPT(dev));
+
+                        if (encoder->type == DRM_MODE_ENCODER_DAC) {
+                                DRM_DEBUG_KMS("Haswell detected DAC encoder, assuming is PCH\n");
+                                return true;
+                        } else {
+                                DRM_DEBUG_KMS("Haswell detected encoder %d, assuming is CPU\n",
+                                                encoder->type);
+                                return false;
+                        }
+                }
+
                 switch (encoder->type) {
                 case INTEL_OUTPUT_EDP:
                         if (!intel_encoder_is_pch_edp(&encoder->base))