[0/3] drm/display: simplify support for transparent DRM bridges

Message

Dmitry Baryshkov July 29, 2023, 8:43 p.m. UTC

Supporting DP/USB-C can result in a chain of several transparent
bridges (PHY, redrivers, mux, etc). This results in drivers having
similar boilerplate code for such bridges.

Next, these drivers are susceptible to -EPROBE_DEFER loops: the next
bridge can either be probed from the bridge->attach callback, when it is
too late to return -EPROBE_DEFER, or from the probe() callback, when the
next bridge might not yet be available, because it depends on the
resources provided by the probing device.

Last, but not least, this results in the the internal knowledge of DRM
subsystem slowly diffusing into other subsystems, like PHY or USB/TYPEC.

To solve all these issues, define a separate DRM helper, which creates
separate aux device just for the bridge. During probe such aux device
doesn't result in the EPROBE_DEFER loops. Instead it allows the device
drivers to probe properly, according to the actual resource
dependencies. The bridge auxdevs are then probed when the next bridge
becomes available, sparing drivers from drm_bridge_attach() returning
-EPROBE_DEFER.

Proposed merge strategy: immutable branch with the drm commit, which is
then merged into PHY and USB subsystems together with the corresponding
patch.

Dmitry Baryshkov (3):
  drm/display: add transparent bridge helper
  phy: qcom: qmp-combo: switch to DRM_SIMPLE_BRIDGE
  usb: typec: nb7vpq904m: switch to DRM_SIMPLE_BRIDGE

 drivers/gpu/drm/display/Kconfig             |   9 ++
 drivers/gpu/drm/display/Makefile            |   2 +
 drivers/gpu/drm/display/drm_simple_bridge.c | 120 ++++++++++++++++++++
 drivers/phy/qualcomm/Kconfig                |   3 +-
 drivers/phy/qualcomm/phy-qcom-qmp-combo.c   |  44 +------
 drivers/usb/typec/mux/Kconfig               |   3 +-
 drivers/usb/typec/mux/nb7vpq904m.c          |  44 +------
 include/drm/display/drm_simple_bridge.h     |  19 ++++
 8 files changed, 156 insertions(+), 88 deletions(-)
 create mode 100644 drivers/gpu/drm/display/drm_simple_bridge.c
 create mode 100644 include/drm/display/drm_simple_bridge.h