Hi,
We've encountered an issue with the RaspberryPi DSI panel that prevented the whole display driver from probing.
The issue is described in detail in the commit 7213246a803f ("drm/vc4: dsi: Only register our component once a DSI device is attached"), but the basic idea is that since the panel is probed through i2c, there's no synchronization between its probe and the registration of the MIPI-DSI host it's attached to.
We initially moved the component framework registration to the MIPI-DSI Host attach hook to make sure we register our component only when we have a DSI device attached to our MIPI-DSI host, and then use lookup our DSI device in our bind hook.
However, all the DSI bridges controlled through i2c are only registering their associated DSI device in their bridge attach hook, meaning with our change above, we never got that far, and therefore ended up in the same situation than the one we were trying to fix for panels.
Since the RaspberryPi panel is the only driver in that situation, whereas it seems like there's a consensus in bridge drivers, it makes more sense to try to mimic the bridge pattern in the panel driver.
However, panels don't have an attach hook, and adding more panel hooks would lead to more path to maintain in each and every driver, while the general push is towards bridges. We also have to make sure that each and every DSI host and device driver behaves the same in order to have expectations to rely on.
The solution I'm proposing is thus done in several steps:
- We get rid of the initial patch to make sure we support the bridge case, and not the odd-panel one.
- Add a function that returns a bridge from a DT node, reducing the amount of churn in each and every driver and making it a real incentive to not care about panels in display drivers but only bridges.
- Add an attach and detach hook into the panel operations, and make it called automatically by the DRM panel bridge.
- Convert the VC4 DSI host to this new bridge function, and the RaspberryPi Panel to the new attach and detach hooks.
If the general approach is agreed upon, other drivers will obviously be converted to drm_of_get_next.
Let me know what you think, Maxime
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Changes from v1: - Change the name of drm_of_get_next function to drm_of_get_bridge - Mention the revert of 87154ff86bf6 and squash the two patches that were reverting that commit - Add some documentation - Make drm_panel_attach and _detach succeed when no callback is there
Maxime Ripard (8): Revert "drm/vc4: dsi: Only register our component once a DSI device is attached" drm/bridge: Add a function to abstract away panels drm/bridge: Add documentation sections drm/bridge: Document the probe issue with MIPI-DSI bridges drm/panel: Create attach and detach callbacks drm/vc4: dsi: Switch to drm_of_get_bridge drm/panel: raspberrypi-touchscreen: Use the attach hook drm/panel: raspberrypi-touchscreen: Remove MIPI-DSI driver
Documentation/gpu/drm-kms-helpers.rst | 12 ++ drivers/gpu/drm/bridge/panel.c | 6 + drivers/gpu/drm/drm_bridge.c | 114 ++++++++++++- drivers/gpu/drm/drm_of.c | 3 + drivers/gpu/drm/drm_panel.c | 47 ++++++ .../drm/panel/panel-raspberrypi-touchscreen.c | 158 +++++++++--------- drivers/gpu/drm/vc4/vc4_drv.c | 2 + drivers/gpu/drm/vc4/vc4_dsi.c | 53 +++--- include/drm/drm_bridge.h | 2 + include/drm/drm_panel.h | 27 +++ 10 files changed, 303 insertions(+), 121 deletions(-)