Update the Qt for Embedded Linux page giving env variables preference

Environment variables are inherited by child processes, whereas command-line
options aren't. Environment variables are therefore preferable for anything
relating to how to interact with the display server.

Change-Id: I5e947065ec19bb19d41ce55310699f11cfe76d52
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>

1 files changed, 16 insertions, 12 deletions

diff --git a/doc/src/platforms/emb-linux.qdoc b/doc/src/platforms/emb-linux.qdoc
index 02d16999..bb1626f1 100644
--- a/doc/src/platforms/emb-linux.qdoc
+++ b/doc/src/platforms/emb-linux.qdoc
@@ -38,8 +38,10 @@
   Linux systems: EGLFS, LinuxFB, KMS, DirectFB, Wayland. The availability of
   these depend on the configuration of Qt. The default platform plugin is also
   device specific. For instance, on many boards eglfs will be chosen as the
-  default one. If the default is not suitable, the \c -platform command-line
-  parameter can be used to request another plugin.
+  default one. If the default is not suitable, the \c QT_QPA_PLATFORM
+  environment variable parameter can be used to request another
+  plugin. Alternatively, for quick tests, the \c -platform command-line can be
+  used with the same syntax.
 
   \section1 Configuring for a Specific Device
 
@@ -168,11 +170,11 @@
   is supported. Note that on some setups the display performance is expected to
   be limited.
 
-  The \c linuxfb plugin allows specifying additional settings by passing them in
-  the \c -platform command-line argument. For example, \c {-platform
-  linuxfb:fb=/dev/fb1} specifies that the framebuffer device \c /dev/fb1 should
-  be used instead of the default \c fb0. Multiple settings can be specfified by
-  separating them with a colon.
+  The \c linuxfb plugin allows specifying additional settings by passing them
+  in the \c QT_QPA_PLATFORM environment variable or \c -platform command-line
+  option. For example, \c {QT_QPA_PLATFORM=linuxfb:fb=/dev/fb1} specifies that
+  the framebuffer device \c /dev/fb1 should be used instead of the default \c
+  fb0. Multiple settings can be specfified by separating them with a colon.
 
   \list
 
@@ -220,11 +222,13 @@
   \section2 Input on linuxfb
 
   To enable keyboard, mouse, touch or tablet support with linuxfb, pass \c
-  {-plugin evdevkeyboard}, \c {-plugin evdevmouse}, \c{-plugin evdevtouch}, or
-  \c {-plugin evdevtablet} on the command-line. Most of these can take a device
-  node parameter, for example \c {-plugin evdevmouse:/dev/event1}, in case the
-  Qt's automatic device discovery (based either on \e libudev or a walkthrough
-  of \c {/dev/input/event*}) is not functional or misbehaving.
+  {QT_QPA_GENERIC_PLUGINS=evdevkeyboard,evdevmouse,evdevtouch,...} in the
+  environment or, alternatively, \c {-plugin evdevkeyboard}, \c {-plugin
+  evdevmouse}, \c{-plugin evdevtouch}, or \c {-plugin evdevtablet} on the
+  command-line. Most of these can take a device node parameter, for example \c
+  {QT_QPA_GENERIC_PLUGINS=evdevmouse:/dev/event1}, in case the Qt's automatic
+  device discovery (based either on \e libudev or a walkthrough of \c
+  {/dev/input/event*}) is not functional or misbehaving.
 
   \section2 Input on eglfs