linux-kernel - Re: [PATCH v3 2/3] OF: Introduce DT overlay support.

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Date:	Fri, 15 Nov 2013 16:13:03 +0000
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Pantelis Antoniou <panto@...oniou-consulting.com>
Cc:	Rob Herring <robherring2@...il.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Matt Porter <matt.porter@...aro.org>,
	Koen Kooi <koen@...inion.thruhere.net>,
	Alison Chaiken <Alison_Chaiken@...tor.com>,
	Dinh Nguyen <dinh.linux@...il.com>,
	Jan Lubbe <jluebbe@...net.de>,
	Alexander Sverdlin <alexander.sverdlin@....com>,
	Michael Stickel <ms@...able.de>,
	Guenter Roeck <linux@...ck-us.net>,
	Dirk Behme <dirk.behme@...il.com>,
	Alan Tull <delicious.quinoa@...il.com>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Michael Bohan <mbohan@...eaurora.org>,
	Ionut Nicu <ioan.nicu.ext@....com>,
	Michal Simek <monstr@...str.eu>,
	Matt Ranostay <mranostay@...il.com>,
	Joel Becker <jlbec@...lplan.org>, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/3] OF: Introduce DT overlay support.

On Fri, 15 Nov 2013 09:34:21 +0100, Pantelis Antoniou <panto@...oniou-consulting.com> wrote:
> Hi Grant,
> 
> On Nov 14, 2013, at 10:22 PM, Grant Likely wrote:
> 
> > On Thu, 14 Nov 2013 11:01:35 +0100, Pantelis Antoniou <panto@...oniou-consulting.com> wrote:
> >> On Nov 14, 2013, at 2:31 AM, Grant Likely wrote:
> >>> On Tue, 12 Nov 2013 10:30:37 +0100, Pantelis Antoniou <panto@...oniou-consulting.com> wrote:
> >>>> On Nov 11, 2013, at 7:42 PM, Grant Likely wrote:
> >>>>> On Fri,  8 Nov 2013 17:06:09 +0200, Pantelis Antoniou <panto@...oniou-consulting.com> wrote:
> >>>> I'm of the opinion that 'platform_device' shouldn't exist at all btw :)
> >>>> Most of it's functionality can pretty easily be subsumed by device proper
> >>>> and the world would be a better place :)
> >>> 
> >>> I'm fine for merging some/all of the platform_device fields into struct
> >>> device. There are a few things, like resources, which would probably be
> >>> useful to have common on all struct device variants. However,
> >>> platform_device is far more about matching drivers to devices. Even if
> >>> all of platform_device went into struct device, there would still need
> >>> to be the platform_bus_type as the collection point for the device
> >>> drivers.
> >>> 
> >> 
> >> We don't really need the resources structures on OF. That information is
> >> present in OF format, which we can use to generate transient resources for
> >> usage with the standard kernel interfaces.
> >> 
> >> BTW, last time I checked resource handling was broken on release.
> >> There are a few patches I sent out fixing it but they were probably ignored.
> > 
> > Please send them again. They probably got lost.
> > 
> >>>>> Can overlays interact in bad ways? If overlay 1 is installed before
> >>>>> overlay 2, what happens if overlay 1 is removed?
> >>>>> 
> >>>> 
> >>>> Yes, they can. It is not something easily fixed; the proper way would
> >>>> be to calculate overlay intersection points and refuse to unload.
> >>> 
> >>> I think this is important. If it cannot be solved immediately, then the
> >>> kernel should enforce overlays always get removed in the reverse order
> >>> that they were added. There may be use-cases that don't like it, but it
> >>> is safe.
> >> 
> >> OK, that makes sense.
> >> 
> >> We are not talking about a global overlay stack though, we're talking about
> >> an overlay stack for overlays that overlap.
> > 
> > I'm actually talking about a global overlay stack. Otherwise you've
> > still got the ever-increasing-phandles problem again.
> > 
> 
> A global overlay stack is easiest. Let's do that first.
> 
> There are use cases for multiple overlay stacks though. Take for instance the
> case where you have multiple plugin connectors.
> 
> Each one can lead to creating a new platform device under ocp, but there is
> no overlap.
> 
> Of course stackable expansion boards work just fine with a global overlay stack :)

Agreed. baby steps...

g.

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