linux-kernel - Re: [PATCH v3 06/13] dt-bindings: reserved-memory: Wakeup Mailbox for Intel processors

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Message-ID: <20250514154248.GA2375202-robh@kernel.org>
Date: Wed, 14 May 2025 10:42:48 -0500
From: Rob Herring <robh@...nel.org>
To: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc: Krzysztof Kozlowski <krzk@...nel.org>, x86@...nel.org,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
	Michael Kelley <mhklinux@...look.com>, devicetree@...r.kernel.org,
	Saurabh Sengar <ssengar@...ux.microsoft.com>,
	Chris Oo <cho@...rosoft.com>, linux-hyperv@...r.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	"Ravi V. Shankar" <ravi.v.shankar@...el.com>,
	Ricardo Neri <ricardo.neri@...el.com>
Subject: Re: [PATCH v3 06/13] dt-bindings: reserved-memory: Wakeup Mailbox
 for Intel processors

On Tue, May 13, 2025 at 03:14:56PM -0700, Ricardo Neri wrote:
> On Mon, May 12, 2025 at 10:32:24AM -0500, Rob Herring wrote:
> > On Tue, May 06, 2025 at 08:23:39PM -0700, Ricardo Neri wrote:
> > > On Tue, May 06, 2025 at 09:10:22AM +0200, Krzysztof Kozlowski wrote:
> > > > On Mon, May 05, 2025 at 10:16:10PM GMT, Ricardo Neri wrote:
> > > > > > If this is a device, then compatibles specific to devices. You do not
> > > > > > get different rules than all other bindings... or this does not have to
> > > > > > be binding at all. Why standard reserved-memory does not work for here?
> > > > > > 
> > > > > > Why do you need compatible in the first place?
> > > > > 
> > > > > Are you suggesting something like this?
> > > > > 
> > > > > reserved-memory {
> > > > > 	# address-cells = <2>;
> > > > > 	# size-cells = <1>;
> > > > > 
> > > > > 	wakeup_mailbox: wakeupmb@...000 {
> > > > > 		reg = < 0x0 0xfff000 0x1000>
> > > > > 	}
> > > > > 
> > > > > and then reference to the reserved memory using the wakeup_mailbox
> > > > > phandle?
> > > > 
> > > > Yes just like every other, typical reserved memory block.
> > > 
> > > Thanks! I will take this approach and drop this patch.
> > 
> > If there is nothing else to this other than the reserved region, then 
> > don't do this. Keep it like you had. There's no need for 2 nodes.
> 
> Thank you for your feedback!
> 
> I was planning to use one reserved-memory node and inside of it a child
> node to with a `reg` property to specify the location and size of the
> mailbox. I would reference to that subnode from the kernel code.
> 
> IIUC, the reserved-memory node is only the container and the actual memory
> regions are expressed as child nodes.
> 
> I had it like that before, but with a `compatible` property that I did not
> need.
> 
> Am I missing anything?

Without a compatible, how do you identify which reserved region is the 
wakeup mailbox? Before you say node name, those are supposed to be 
generic though we failed to enforce anything for /reserved-memory child 
nodes.

Rob