drm/msm: default separate_gpu_kms to auto selection

On platforms with multiple display subsystems, such as SA8775P, the GPU
binds to the first display subsystem that probes. This implicit binding
prevents subsequent display subsystems from probing successfully,
breaking multi-display support.

Use the tristate separate_gpu_kms module parameter with the default
value set to auto (-1). In auto mode, the driver selects the binding
behavior based on the number of GPUs and display subsystems. This allows
display subsystems to probe independently when required, while
preserving the existing single-card behavior on simpler systems.

The separate_gpu_kms module parameter has the following semantics:

  -1 (auto, default):
     Select the binding mode based on hardware topology. If exactly one
     GPU and one display subsystem are present, bind them together to
     form a single DRM device. Otherwise, expose the GPU and display
     subsystems as separate DRM devices.

   0:
     Always bind the GPU and display together to form a single DRM
     device.

   1:
     Always expose the GPU and display subsystems as separate DRM
     devices.

Additionally, ensure that display subsystems are always exposed as
separate DRM devices when no recognized Adreno GPU is present,
regardless of the separate_gpu_kms setting.

This ensures correct probing on multi-display platforms without
affecting single-display, single-GPU systems.

Signed-off-by: Mahadevan P <mahadevan.p@oss.qualcomm.com>
Patchwork: https://patchwork.freedesktop.org/patch/756649/
Link: https://lore.kernel.org/r/20260928-separate_gpu_kms-v4-1-3f33175de133@oss.qualcomm.com
Acked-by: Rob Clark <robin.clark@oss.qualcomm.com> # on IRC
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>

0 files changed, 0 insertions, 0 deletions