linux-kernel - Re: [PATCH] staging: vc04_services: vchiq_arm: Create platform

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Message-ID: <Y6l3B8QOdkY9adLh@kroah.com>
Date:   Mon, 26 Dec 2022 11:27:19 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Stefan Wahren <stefan.wahren@...e.com>,
        Umang Jain <umang.jain@...asonboard.com>,
        linux-staging@...ts.linux.dev,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Florian Fainelli <f.fainelli@...il.com>,
        Adrien Thierry <athierry@...hat.com>,
        Dan Carpenter <error27@...il.com>,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        Phil Elwell <phil@...pberrypi.com>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Kieran Bingham <kieran.bingham@...asonboard.com>
Subject: Re: [PATCH] staging: vc04_services: vchiq_arm: Create
 platform_device per device

On Mon, Dec 26, 2022 at 12:06:53PM +0200, Laurent Pinchart wrote:
> On Fri, Dec 23, 2022 at 03:48:11PM +0100, Greg Kroah-Hartman wrote:
> > On Fri, Dec 23, 2022 at 12:24:22PM +0100, Stefan Wahren wrote:
> > > i vaguely remember the discussion how to represent audio and camera
> > > interface in the device tree. Representing as child nodes of the VC4 has
> > > been rejected on the device tree mailing some years ago, because this
> > > doesn't represent the physical (hardware) wiring. It's still possible to
> > > access e.g. the camera interface from the ARM.
> > > 
> > > The whole approach with using a separate binding for all the firmware stuff
> > > lead to a lot of trouble on the Raspberry Pi platform (ugly dependencies
> > > between firmware, DT and kernel). So i would like to avoid this here. In
> > > case the current implementation is a no go, how about letting the ARM core
> > > discover the available interfaces e.g. via mailbox interface?
> > > 
> > > For more inspiration take a look at this old thread [1]
> > 
> > Yes, that's the proper way to do this please!  This should be a bus and
> > dynamically add the devices when found, it is NOT a platform device
> > anymore.
> 
> I'm fine with making this a bus, but when it comes to dynamically adding
> devices, that depends on the firmware exposing an interface to enumerate
> those devices. If that's not possible, are you fine with a custom bus
> and hardcoded children device instantiation in the VCHIQ driver ?

Yes, that is at least a step forward and is not abusing the platform
device/driver code.

thanks,

greg k-h