[Freedreno] [PATCH v2 00/34] component: Make into an aggregate bus

[Andrzej Hajda]

Hi Stephen,

On 06.10.2021 21:37, Stephen Boyd wrote:
> This series is from discussion we had on reordering the device lists for
> drm shutdown paths[1]. I've introduced an 'aggregate' bus that we put
> the aggregate device onto and then we probe the aggregate device once
> all the components are probed and call component_add(). The probe/remove
> hooks are where the bind/unbind calls go, and then a shutdown hook is
> added that can be used to shutdown the drm display pipeline at the right
> time.
> 
> This works for me on my sc7180 board. I no longer get a warning from i2c
> at shutdown that we're trying to make an i2c transaction after the i2c
> bus has been shutdown. There's more work to do on the msm drm driver to
> extract component device resources like clks, regulators, etc. out of
> the component bind function into the driver probe but I wanted to move
> everything over now in other component drivers before tackling that
> problem.


As I understand you have DSI host with i2c-controlled DSI bridge. And 
there is an issue that bridge is shutdown before msmdrm. Your solution 
is to 'adjust' device order on pm list.
I had similar issue and solved it locally by adding notification from 
DSI bridge to DSI host that is has to be removed: mipi_dsi_detach, this 
notification escalates in DSI host to component_del and this allow to 
react properly.

Advantages:
- it is local (only involves DSI host and DSI device),
- it does not depend on PM internals,
- it can be used in other scenarios as well - unbinding DSI device driver

Disadvantage:
- It is DSI specific (but this is your case), I have advertised some 
time ago more general approach [1][2].

[1]: https://static.sched.com/hosted_files/osseu18/0f/deferred_problem.pdf
[2]: https://lwn.net/Articles/625454/


Regards
Andrzej