diff --git a/doc/src/platforms/emb-linux.qdoc b/doc/src/platforms/emb-linux.qdoc index 8bf49e75eb423b7392987642ac790bc3c5513070..9cfa82f85aa8bb96402475cb23a32952c8dd570a 100644 --- a/doc/src/platforms/emb-linux.qdoc +++ b/doc/src/platforms/emb-linux.qdoc @@ -768,16 +768,35 @@ configuration via \c QT_QPA_EGLFS_KMS_CONFIG are supported. Some settings, such as \c hwcursor and \c pbuffers are not applicable however. - By default the backend will find the first available display and pick the EGL - layer that corresponds to it. When necessary, this can be overridden by + By default the backend will automatically choose the correct EGL layer for the + default plane of each output. When necessary, this can be overridden by setting the \c QT_QPA_EGLFS_LAYER_INDEX environment variable to the index of - the desired layer. To see which layers are available, and to debug potential - startup issues, enable the logging category \c qt.qpa.eglfs.kms. In some cases - it may be necessary to perform a video mode set on application startup even - when the screen reports that the desired resolution is already set. This is - normally optimized away, but if the screen stays powered down, try setting the - environment variable \c QT_QPA_EGLFS_ALWAYS_SET_MODE to a non-zero value and - relaunch the application. + the desired layer. This approach does not currently support multiple outputs, + so its usage should be limited to systems with a single screen. To see which + layers are available, and to debug potential startup issues, enable the + logging category \c qt.qpa.eglfs.kms. + + In some cases it may be necessary to perform a video mode set on application + startup even when the screen reports that the desired resolution is already + set. This is normally optimized away, but if the screen stays powered down, + try setting the environment variable \c QT_QPA_EGLFS_ALWAYS_SET_MODE to a + non-zero value and relaunch the application. + + To configure the behavior of the EGLStream object used by the backend, use the + \c QT_QPA_EGLFS_STREAM_FIFO_LENGTH environment variable. This assumes that + \c KHR_stream_fifo is supported by the target system. By default the stream + operates in mailbox mode. To switch to FIFO mode, set a value of 1 or + greater. The value specifies the maximum number of frames the stream can hold. + + On some systems it may become necessary to target a specific overlay plane + through a pre-defined connector. Just forcing a layer index via + \c QT_QPA_EGLFS_LAYER_INDEX does not perform plane configuration and is therefore + not suitable in itself. Instead, in such special scenarios use the + \c QT_QPA_EGLFS_KMS_CONNECTOR_INDEX and \c QT_QPA_EGLFS_KMS_PLANE_INDEX + environment variables. When these are set, only the specified connector and + plane will be in use, all other outputs will get ignored. The backend will + take care of picking the EGL layer that corresponds to the desired plane, and + the configuring of the plane. \section2 Touch input in systems with multiple screens on KMS/DRM