linux-kernel - Re: [PATCH v2 0/6] Device tree support for Hyper-V VMBus driver

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Date:   Tue, 7 Feb 2023 18:44:30 -0800
From:   Saurabh Singh Sengar <ssengar@...ux.microsoft.com>
To:     Rob Herring <robh@...nel.org>
Cc:     krzysztof.kozlowski+dt@...aro.org, kys@...rosoft.com,
        haiyangz@...rosoft.com, wei.liu@...nel.org, decui@...rosoft.com,
        daniel.lezcano@...aro.org, tglx@...utronix.de,
        virtualization@...ts.linux-foundation.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org, mikelley@...rosoft.com,
        ssengar@...rosoft.com
Subject: Re: [PATCH v2 0/6] Device tree support for Hyper-V VMBus driver

On Tue, Feb 07, 2023 at 11:53:54AM -0600, Rob Herring wrote:
> On Wed, Feb 1, 2023 at 10:34 AM Saurabh Singh Sengar
> <ssengar@...ux.microsoft.com> wrote:
> >
> > On Wed, Feb 01, 2023 at 08:51:46AM -0600, Rob Herring wrote:
> > > On Tue, Jan 31, 2023 at 06:04:49PM -0800, Saurabh Singh Sengar wrote:
> > > > On Tue, Jan 31, 2023 at 02:27:51PM -0600, Rob Herring wrote:
> > > > > On Tue, Jan 31, 2023 at 12:10 PM Saurabh Sengar
> > > > > <ssengar@...ux.microsoft.com> wrote:
> > > > > >
> > > > > > This set of patches expands the VMBus driver to include device tree
> > > > > > support.
(...)
> > You are right we have define a new config flag in Kconfig, and selected CONFIG_OF
> > and CONFIG_OF_EARLY_FLATTREE. We are working on upstreaming that patch as well
> > however that will be a separate patch series.
> 
> Fair enough, but that should come first IMO. Really I just want to see
> a complete picture. That can be a reference to a git branch(es) or
> other patch series. But again, what I want to see in particular is the
> actual DT and validation run on it.

Thank you for explaining the concern. I now understand it fully. I have come to the
realization that enabling the vmbus device tree should not be impacted by any changes.
To address this, I will add the following lines to the HYPERV Kconfig definition I
used for testing:

	select OF if !ACPI
	select OF_EARLY_FLATTREE if !ACPI"

> 
> > > Also see my comment on v1 about running DT validation on your dtb. I'm
> > > sure running it would point out other issues. Such as the root level
> > > comaptible string(s) need to be documented. You need cpu nodes,
> > > interrupt controller, timers, etc. Those all have to be documented.
> >
> > I will be changing the parent node to soc node as suggested by Krzysztof
> > in other thread.
> 
> Another issue yes, but orthogonal to my comments.
> 
> >
> > soc {
> >         #address-cells = <2>;
> >         #size-cells = <2>;
> 
> You are missing 'ranges' here. Without it, addresses aren't translatable.
> 
> You are also missing 'compatible = "simple-bus";'. This happens to
> work on x86 because of legacy reasons, but we don't want new cases
> added.

I am a bit unclear on the reason for adding the ranges property in the root node.
To provide more context, I have included my full device tree below. I believe that
having the ranges property in the VMBus device node is sufficient. Please let me
know if this can be improved.


/dts-v1/;

/ {
	#address-cells = <0>;
	#size-cells = <0>;
	model = "microsoft,test";

	cpus {
		#address-cells = <0x01>;
		#size-cells = <0x00>;

		cpu@0 {
			device_type = "cpu";
			reg = <0x00>;
			status = "okay";
		};

		cpu@1 {
			device_type = "cpu";
			reg = <0x01>;
			status = "okay";
		};
	};

        vmbus@...000000 {
            #address-cells = <2>;
            #size-cells = <2>;                            
            compatible = "microsoft,vmbus";             
            ranges = <0x0f 0xf0000000 0x0f 0xf0000000 0x0 0x10000000>;        
       };
};

> 
> >
> >         vmbus@...000000 {
> >             #address-cells = <2>;
> >             #size-cells = <1>;
> >             compatible = "Microsoft,vmbus";
> 
> 'Microsoft' is not a vendor prefix.
> 
> >             ranges = <0x00 0x00 0x0f 0xf0000000 0x10000000>;
> >         };
> > };
> >
> > This will be sufficient.
> 
> All these comments are unnecessary because the tools will now check
> these things and we shouldn't have to.

Agree, and its fixed in latest version.

Regards,
Saurabh
> 
> Rob