Re: [PATCH] media: venus: Synchronize probe() between venus_core and enc/dec

[Bryan O'Donoghue]

On 25/10/2021 16:30, Tadeusz Struk wrote:
> No, we want a hard stop here. At this point the venus_core probe()
> has finished and it failed. Returning -EPROBE_DEFER here will just
> cause it to loop infinitely.

I don't think there's any guarantee at all, that core probe() has 
completed at that point.

of_platform_populate() doesn't guarantee ordering of the probe() 
completing before or after the probe() of the platform drivers that are 
associated with the devices in of_platform_populate().

When you think it about it can't do that and you wouldn't want it to do 
that since a device might have a legitimate reason to EPROBE_DEFER

As an example core could call of_platform_populate() and then as a 
ridiculous example go to sleep for five seconds - in which case it is 
perfectly possible the encoder and decoder probe() functions will bug 
out illegitimately waiting because of core->state != CORE_INIT

This is a problem we have and still haven't solved in 
drivers/usb/dwc3/dwc3-qcom.c::probe() and child devices 
drivers/usb/dwc3/dwc3-qcom.c

Here:
https://patches.linaro.org/cover/470387/

There's no serialisation guarantee between parent and child on 
of_platform_populate() - at least none I'm aware of.

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bod