backends/drm: relax direct scanout rules for color management

The GL renderer currently doesn't apply any transformations except clipping,
so allowing direct scanout is okay as long as colorimetry and transfer
function match.

src/backends/drm/drm_egl_layer.cpp

@@ -90,10 +90,14 @@ bool EglGbmLayer::doAttemptScanout(GraphicsBuffer *buffer, const ColorDescriptio
     if (directScanoutDisabled) {
         return false;
     }
-    if (color != m_pipeline->colorDescription() || m_pipeline->output()->channelFactors() != QVector3D(1, 1, 1) || m_pipeline->iccProfile()) {
+    if (m_pipeline->output()->channelFactors() != QVector3D(1, 1, 1) || m_pipeline->iccProfile()) {
         // TODO use GAMMA_LUT, CTM and DEGAMMA_LUT to allow direct scanout with HDR
         return false;
     }
+    const auto &targetColor = m_pipeline->colorDescription();
+    if (color.colorimetry() != targetColor.colorimetry() || color.transferFunction() != targetColor.transferFunction()) {
+        return false;
+    }
     // kernel documentation says that
     // "Devices that don’t support subpixel plane coordinates can ignore the fractional part."
     // so we need to make sure that doesn't cause a difference vs the composited result