linux-kernel - Re: [RESEND PATCH 2/2] usb: dwc3: pci add property to allow user space role switch

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Message-ID: <YSXwkKJ53d/uwnhy@kuha.fi.intel.com>
Date:   Wed, 25 Aug 2021 10:26:08 +0300
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Felipe Balbi <balbi@...nel.org>
Cc:     Nehal Bakulchandra Shah <Nehal-Bakulchandra.shah@....com>,
        gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, kun.liu2@....com,
        alexander.deucher@....com
Subject: Re: [RESEND PATCH 2/2] usb: dwc3: pci add property to allow user
 space role switch

On Wed, Aug 25, 2021 at 10:01:05AM +0300, Heikki Krogerus wrote:
> On Wed, Aug 25, 2021 at 08:55:41AM +0300, Felipe Balbi wrote:
> > 
> > Hi,
> > 
> > Nehal Bakulchandra Shah <Nehal-Bakulchandra.shah@....com> writes:
> > 
> > > For AMD platform there is a requirement to enable user space role
> > > switch from host to device and device to host as customer platform is not
> > > completely capable of OTG i.e. with type C controller it does not have PD
> > > to support role switching. Hence, based ACPI/EC interrupt role switch is
> > > triggered by the usemode script running in background.
> >                    usermode ?
> 
> Couldn't you capture that ACPI/EC interrupt in kernel?
> 
> > > Signed-off-by: Nehal Bakulchandra Shah <Nehal-Bakulchandra.shah@....com>
> > 
> > I'm okay with this, just wondering if we need to Document the property
> > somewhere.
> > 
> > @Heikki, is there a place to document these private properties that's
> > not on DT binding document?
> 
> The build-in properties are not documented separately. I've always
> tried to supply DT bindings for all new properties I've proposed.
> 
> In this case though, do we need the new property at all? Why not just
> register a normal USB role switch on this platform? It can be either a
> dummy role switch that only passes the user space input to dwc3, or,
> perhaps ideally, it would also be a driver that captures that ACPI/EC
> event/notification and then passes the information from it to dwc3.

Please ignore the above question. Sorry. Let me try again...

The question is: why not just capture that ACPI/EC "interrupt" in
kernel and then just use that information to set the dwc3 role switch?
No extra properties needed.


thanks,

-- 
heikki