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

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Message-ID: <20230201145146.GA3352796-robh@kernel.org>
Date:   Wed, 1 Feb 2023 08:51:46 -0600
From:   Rob Herring <robh@...nel.org>
To:     Saurabh Singh Sengar <ssengar@...ux.microsoft.com>
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, 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?

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.

Rob