drm_hwcomposer: pre-filter modes provided to HWC2

Currently LocalDisplayAdapter in AOSP filters out similar modes based
on their currently limited supported attributes: width/height/refresh.

This leads to a situation where important modes are discarded, like the
preferred mode and/or the active mode, leading SurfaceFlinger to select
an unwanted and potentially invalid  mode in the list provided by
drm-hwcomposer to HWC2.

Let's pre-filter the modes provided to HWC2 by :
- systematically adding the preferred mode
- systematically adding the current active mode, if different
  from preferred mode
- keeping the interlaced modes filtering-out if no other non-interlace
  modes with same widthXheight exists (for HD-Ready 1080i TVs or CVBS)
- discarding modes if a similar mode with same widthXheight@refresh was
  already selected for HWC2

This mimics the behavior of LocalDisplayAdapter filtering algorithm,
but keeps the important modes from the DRM Point Of View and drops the
duplicate modes while keeping the mode ordering from DRM in account.

This local filtering should ultimately go out when HWC2 can actually
handle mode Attributes to describe Preferred mode, Interlaced, 3D...
and LocalDisplayAdapter uses these Attributes for filtering duplicate
modes.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Tested-by: John Stultz <john.stultz@linaro.org>

1 files changed, 59 insertions, 17 deletions

diff --git a/drmhwctwo.cpp b/drmhwctwo.cpp
index b96eb31..9268cdc 100644
--- a/drmhwctwo.cpp
+++ b/drmhwctwo.cpp
@@ -399,17 +399,37 @@ HWC2::Error DrmHwcTwo::HwcDisplay::GetDisplayConfigs(uint32_t *num_configs,
     }
   }
 
-  uint32_t idx = 0;
+  // Since the upper layers only look at vactive/hactive/refresh, height and
+  // width, it doesn't differentiate interlaced from progressive and other
+  // similar modes. Depending on the order of modes we return to SF, it could
+  // end up choosing a suboptimal configuration and dropping the preferred
+  // mode. To workaround this, don't offer interlaced modes to SF if there is
+  // at least one non-interlaced alternative and only offer a single WxH@R
+  // mode with at least the prefered mode from in DrmConnector::UpdateModes()
+
+  // TODO: Remove the following block of code until AOSP handles all modes
+  std::vector<DrmMode> sel_modes;
+
+  // Add the preferred mode first to be sure it's not dropped
+  auto mode = std::find_if(connector_->modes().begin(),
+                           connector_->modes().end(), [&](DrmMode const &m) {
+                             return m.id() ==
+                                    connector_->get_preferred_mode_id();
+                           });
+  if (mode != connector_->modes().end())
+    sel_modes.push_back(*mode);
+
+  // Add the active mode if different from preferred mode
+  if (connector_->active_mode().id() != connector_->get_preferred_mode_id())
+    sel_modes.push_back(connector_->active_mode());
+
+  // Cycle over the modes and filter out "similar" modes, keeping only the
+  // first ones in the order given by DRM (from CEA ids and timings order)
   for (const DrmMode &mode : connector_->modes()) {
-    if (configs && idx >= *num_configs)
-      break;
-    // Since the upper layers only look at vactive/hactive/refresh, it doesn't
-    // differentiate interlaced from progressive modes. Depending on the order
-    // of modes we return to SF, it could end up choosing a suboptimal
-    // configuration.
-    // To workaround this, don't offer interlaced modes to SF if there is at
-    // least one non-interlaced alternative.
-    //
+    // TODO: Remove this when 3D Attributes are in AOSP
+    if (mode.flags() & DRM_MODE_FLAG_3D_MASK)
+      continue;
+
     // TODO: Remove this when the Interlaced attribute is in AOSP
     if (mode.flags() & DRM_MODE_FLAG_INTERLACE) {
       auto m = std::find_if(connector_->modes().begin(),
@@ -419,14 +439,36 @@ HWC2::Error DrmHwcTwo::HwcDisplay::GetDisplayConfigs(uint32_t *num_configs,
                                      m.h_display() == mode.h_display() &&
                                      m.v_display() == mode.v_display();
                             });
-      if (m != connector_->modes().end())
-        continue;
-    }
-    if (configs) {
-      configs[idx++] = mode.id();
-    } else {
-      idx++;
+      if (m == connector_->modes().end())
+        sel_modes.push_back(mode);
+
+      continue;
     }
+
+    // Search for a similar WxH@R mode in the filtered list and drop it if
+    // another mode with the same WxH@R has already been selected
+    // TODO: Remove this when AOSP handles duplicates modes
+    auto m = std::find_if(sel_modes.begin(), sel_modes.end(),
+                          [&mode](DrmMode const &m) {
+                            return m.h_display() == mode.h_display() &&
+                                   m.v_display() == mode.v_display() &&
+                                   m.v_refresh() == mode.v_refresh();
+                          });
+    if (m == sel_modes.end())
+      sel_modes.push_back(mode);
+  }
+
+  auto num_modes = static_cast<uint32_t>(sel_modes.size());
+  if (!configs) {
+    *num_configs = num_modes;
+    return HWC2::Error::None;
+  }
+
+  uint32_t idx = 0;
+  for (const DrmMode &mode : sel_modes) {
+    if (idx >= *num_configs)
+      break;
+    configs[idx++] = mode.id();
   }
   *num_configs = idx;
   return HWC2::Error::None;