The code path added by commit 69e4b8e6 (xfree86: attempt to autoconfig
gpu slave devices (v3)) assumes that it will only be run if the primary
device on the screen is the first device in xf86configptr->conf_device_lst.
While this is true most of the time, there are two specific cases where
this assumption fails.
First, if the first device in conf_device_lst is assigned to a different
seat than the running X server, it will be skipped by the previous
FIND_SUITABLE macro usage. Second, if the primary device was explicitly
assigned to the screen but auto_gpu_device is still set and no secondary
devices were explicitly listed, that device may not be the first device
in conf_device_lst.
When the first device in conf_device_lst is not the primary device
assigned to the screen, two problems emerge. First, the first device in
conf_device_lst will never be assigned to the screen as a secondary
device. Second, the primary device is additionally assigned to the
screen as a secondary device. The combination of these problems causes
certain otherwise valid configurations to be invalid. For example, if a
primary device is assigned to a screen and a secondary device is listed
in the config but not explicitly assigned to the screen, then one order
of the device sections results in a usable PRIME or Reverse PRIME setup
and the other order does not.
This commit removes the assumption that the primary device is the first
device in conf_device_lst by starting the loop from the start of
conf_device_lst and skipping the primary device when it is encountered.
Signed-off-by: Jacob Cherry <jcherry@nvidia.com>
The X server accepts requests from client applications to create windows,
which are (normally rectangular) "virtual screens" that the client program
can draw into.
Windows are then composed on the actual screen by the X server
(or by a separate composite manager) as directed by the window manager,
which usually communicates with the user via graphical controls such as buttons
and draggable titlebars and borders.
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