Re: [PATCH 0/3] Implement role-switch notifications from dwc3-drd to dwc3-qcom

[Bryan O'Donoghue <bryan.odonoghue@linaro.org>]

On 25/08/2021 06:51, Felipe Balbi wrote:
>> Hi Peter, I took a proper look at this again, hoping to find a way to
>> pass a callback pointer from dwc3-qcom to the dwc3 core, that can be
>> called from __dwc3_set_mode() to inform the Qualcomm glue about mode
>> changes.
> I would rather keep the strict separation between glue and core.

# 1 __dwc3_set_mode
Felipe wants to keep a strict separation between core and glue

# notifier
Requires the core probe() to complete before the glue probe to work 
reliably. This then would lead us to remaking the dwc3-qcom::probe() to 
facilitate probe deferral.

We can be sure bugs would be introduced in this process.

AFAIK Felipe is not opposed to this, Bjorn likes it

# 2 extcon
Works but a) is deprecated and b) even if it weren't deprecated has no 
way to layer the messages - that I know of.

# 3 USB role switch
Already in-place for the producer {phy, type-c port, usb-gpio typec, 
google ecros} to consumer dwc-core. It already has a layering 1:1 of 
that array of producers to the consumer.

Unlike extcon though it cannot relay messages to more than one consumer.

As I see it we can either

A. Rewrite the dwc3-qcom probe to make it synchronous with dwc3-core 
probe taking the hit of whatever bugs get thrown up as a result of that 
over the next while, potentially years.

B. Use USB role switch in some format.

Either
X. as I've submitted here based on a bit of code in dwc3-core or

Y. maybe trying to hide the "relay" aspect in DTS and USB role-switch core

It seems to me our choices are notifier + pain and churn - perhaps low, 
perhaps high or USB role switch

3.B.X works and is what has been submitted here but, if it is 
objectionable is 3.B.Y viable ?

As in make USB role switch propigate to multiple consumers via DTS and 
whatever additional work is required in the role-switch layer ?

+ Heikki on that one.

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bod