linux-kernel - Re: [PATCH v4 0/1] pstore/ram: add Device Tree bindings

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Message-ID: <20160621204121.GA1595@rob-hp-laptop>
Date:	Tue, 21 Jun 2016 15:41:21 -0500
From:	Rob Herring <robh@...nel.org>
To:	Kees Cook <keescook@...omium.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Greg Hackmann <ghackmann@...gle.com>,
	Arnd Bergmann <arnd@...db.de>,
	Markus Pargmann <mpa@...gutronix.de>,
	Olof Johansson <olof@...om.net>,
	Brian Norris <computersforpeace@...il.com>,
	Anton Vorontsov <anton@...msg.org>,
	Colin Cross <ccross@...roid.com>,
	Lee Campbell <leecam@...gle.com>,
	Tony Luck <tony.luck@...el.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v4 0/1] pstore/ram: add Device Tree bindings

On Tue, Jun 14, 2016 at 09:40:47PM -0700, Kees Cook wrote:
> On Tue, Jun 14, 2016 at 2:59 PM, Rob Herring <robh@...nel.org> wrote:
> > On Fri, Jun 10, 2016 at 03:50:58PM -0700, Kees Cook wrote:
> >> This is a "v4" of Greg Hackmann's DT bindings for ramoops. This is
> >> what I'm going to land in the pstore tree unless there are strong and
> >> convincing arguments against it. :)
> >>
> >> I made a number of changes based people's feedback, and I want to get
> >> it unblocked. This patch is already carried by Android, and it doesn't
> >> need to be out of tree.
> >>
> >> To respond to Arnd's comment: I like this as the ramoops node, not the
> >> pstore node, since it describes the ramoops backend, not the pstore
> >> subsystem, which has different controls, and can only have one backend
> >> at a time. So it doesn't make sense to me to have this have a redundant
> >> extra pstore node, since the very presence of ramoops implies pstore.
> >
> > Either I don't follow or you don't get Arnd's comment...
> >
> > IIRC, his suggestion which I agree with was to remove the memory-region
> > phandle and just move all the properties into the reserved memory node
> > directly. This simplifies things such that we are just describing
> > properties of a chunk of memory rather than a Linux specific node for
> > virtual driver.
> 
> Ah! Okay, I'm a DT newbie, so I think I misunderstood Arnd. :) If it's
> easy, can you create a patch for that against the v4 I sent of Greg's
> patch? I'm not sure how to do what you're suggesting. :)

While I want to see this merged, I'm not going to get to anything soon. 
So here's a DT example of what I mean. This will in addition need an 
of_platform_populate call on the /reserved-memory node to get the 
platform device created.

{/
        reserved-memory {
		#address-cells = <1>;
		#size-cells = <1>;
		ranges;

		/* global autoconfigured region for contiguous allocations */
		linux,cma {
			compatible = "shared-dma-pool";
			reusable;
			size = <0x4000000>;
			alignment = <0x2000>;
			linux,cma-default;
		};

		ramoops@...00000 {
			compatible = "ramoops";
			reg = <0x78000000 0x8000>;
			record-size = <0x4000>;
			console-size = <0x4000>
		};
	};
};

Rob