doc: improve the T440 documentation a bit

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

diff --git a/doc/t440-support.dox b/doc/t440-support.dox
index 8e2f9c234db263742c3a0d90fc2524980bbc938d..652a6d0b0613869798076d1dbb8d70ea5ddbe932 100644 (file)
--- a/doc/t440-support.dox
+++ b/doc/t440-support.dox
@@ -25,36 +25,77 @@ property.
 
 @section t440_support_btn_size Size of the buttons
 
+The size of the buttons matches the visual markings on this touchpad.
+The width of the left and right buttons is approximately 42% of the
+touchpad's width, the middle button is centered and assigned 16% of the
+touchpad width.
+
 The line of the buttons is 5mm from the top edge of the touchpad,
 measurements of button presses showed that the size of the buttons needs to
 be approximately 10mm high to work reliable (especially when using the
 thumb to press the button).
 
-The width of the left and right buttons is approximately 42% of the
-touchpad's width, the middle button is centered and should be assigned
-approximately 16% of the touchpad width.
-
 @section t440_support_btn_behavior Button behavior
 
 Movement in the top button area does not generate pointer movement. These
 buttons are not replacement buttons for the bottom button area but have
-their own behavior.
-Semantically attached to the trackstick device, libinput re-routes events
-from these buttons to appear through the trackstick device. The top button
-areas work even if the touchpad is disabled but will be disabled when the
-trackstick device is disabled.
+their own behavior. Semantically attached to the trackstick device, libinput
+re-routes events from these buttons to appear through the trackstick device.
+
+@dot
+digraph top_button_routing
+{
+       rankdir="LR";
+       node [shape="box";]
+
+       trackstick [label="trackstick kernel device"];
+       touchpad [label="touchpad kernel device"];
+
+       subgraph cluster0 {
+               bgcolor = floralwhite
+               label = "libinput"
 
-If the finger starts inside the top area and moves outside the button area
-the finger is treated as dead and must be lifted to generate future buttons.
-Likewise, movement into the top button area does not trigger button events, a click
-has to start inside this area to take effect.
+               libinput_ts [label="trackstick libinput_device"
+                            style=filled
+                            fillcolor=white];
+               libinput_tp [label="touchpad libinput_device"
+                            style=filled
+                            fillcolor=white];
+
+               libinput_tp -> libinput_ts [constraint=false
+                                           color="red4"];
+       }
+
+       trackstick -> libinput_ts [arrowhead="none"]
+       touchpad -> libinput_tp [color="red4"]
+
+       events_tp [label="other touchpad events"];
+       events_topbutton [label="top sofware button events"];
+
+       libinput_tp -> events_tp [arrowhead="none"]
+       libinput_ts -> events_topbutton [color="red4"]
+}
+@enddot
+
+
+The top button areas work even if the touchpad is disabled but will be
+disabled when the trackstick device is disabled. If the finger starts inside
+the top area and moves outside the button area the finger is treated as dead
+and must be lifted to generate future buttons.  Likewise, movement into the
+top button area does not trigger button events, a click has to start inside
+this area to take effect.
 
 @section t440_support_identification Kernel support
 
-The firmware on touchpads providing top software buttons is buggy and
-announces wrong ranges. <a href="https://lkml.org/lkml/2014/3/7/722">Kernel
-patches</a> are required; these fixes are available in kernels
-3.14.1, 3.15 and later but each touchpad needs a separate fix.
+The firmware on the first generation of touchpads providing top software
+buttons is buggy and announces wrong ranges.
+<a href="https://lkml.org/lkml/2014/3/7/722">Kernel patches</a> are required;
+these fixes are available in kernels 3.14.1, 3.15 and later but each
+touchpad needs a separate fix.
+
+The October 2014 refresh of these laptops do not have this firmware bug
+anymore and should work without per-device patches, though
+<a href="http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=02e07492cdfae9c86e3bd21c0beec88dbcc1e9e8">this kernel commit</a> is required.
 
 For a complete list of supported touchpads check <a
 href="http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/input/mouse/synaptics.c">the