On Fri, Jul 10, 2020 at 5:02 PM Douglas Anderson dianders@chromium.org wrote:
I found that if I ever had a little mistake in my kernel config, or device tree, or graphics driver that my system would sit in a loop at bootup trying again and again and again. An example log was:
Why do we care about optimizing the error case?
msm ae00000.mdss: bound ae01000.mdp (ops 0xffffffe596e951f8) msm_dsi ae94000.dsi: ae94000.dsi supply gdsc not found, using dummy regulator msm_dsi_manager_register: failed to register mipi dsi host for DSI 0 [drm:ti_sn_bridge_probe] *ERROR* could not find any panel node ...
I finally tracked it down where this was happening:
- msm_pdev_probe() is called.
- msm_pdev_probe() registers drivers. Registering drivers kicks off processing of probe deferrals.
- component_master_add_with_match() could return -EPROBE_DEFER. making msm_pdev_probe() return -EPROBE_DEFER.
- When msm_pdev_probe() returned the processing of probe deferrals happens.
- Loop back to the start.
It looks like we can fix this by marking "mdss" as a "simple-bus". I have no idea if people consider this the right thing to do or a hack. Hopefully it's the right thing to do. :-)
It's a simple test. Do the child devices have any dependency on the parent to probe and/or function? If so, not a simple-bus.
Once I do this I notice that my boot gets marginally faster (you don't need to probe the sub devices over and over) and also if I
Can you quantify that?
Have you run with devlinks enabled. You need a command line option to enable. That too should reduce deferred probes.
have a problem it doesn't loop forever (on my system it still gets upset about some stuck clocks in that case, but at least I can boot up).
Deferred probe only runs when a device is added, so it's not like it is continually running.
Rob