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

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Date:   Wed, 1 Feb 2023 08:34:55 -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 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.
> > > >
> > > > The first two patches enable compilation of Hyper-V APIs in a non-ACPI
> > > > build.
> > > >
> > > > The third patch converts the VMBus driver from acpi to more generic
> > > > platform driver.
> > > >
> > > > Further to add device tree documentation for VMBus, it needs to club with
> > > > other virtualization driver's documentation. For this rename the virtio
> > > > folder to more generic hypervisor, so that all the hypervisor based
> > > > devices can co-exist in a single place in device tree documentation. The
> > > > fourth patch does this renaming.
> > > >
> > > > The fifth patch introduces the device tree documentation for VMBus.
> > > >
> > > > The sixth patch adds device tree support to the VMBus driver. Currently
> > > > this is tested only for x86 and it may not work for other archs.
> > > 
> > > I can read all the patches and see *what* they do. You don't really
> > > need to list that here. I'm still wondering *why*. That is what the
> > > cover letter and commit messages should answer. Why do you need DT
> > > support? How does this even work on x86? FDT is only enabled for
> > > CE4100 platform.
> > 
> > HI Rob,
> > 
> > Thanks for your comments.
> > We are working on a solution where kernel is booted without ACPI tables to keep
> > the overall system's memory footprints slim and possibly faster boot time.
> > We have tested this by enabling CONFIG_OF for x86.
> 
> It's CONFIG_OF_EARLY_FLATTREE which you would need and that's not user 
> selectable. At a minimum, you need some kconfig changes. Where are 
> those?

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.

> 
> 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.

soc {
        #address-cells = <2>;
        #size-cells = <2>;

	vmbus@...000000 {
            #address-cells = <2>;
            #size-cells = <1>;
            compatible = "Microsoft,vmbus";
            ranges = <0x00 0x00 0x0f 0xf0000000 0x10000000>;
        };
};

This will be sufficient.

Regards,
Saurabh

> 
> Rob