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

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Message-ID: <CAL_JsqKHPg4ybcmMV2fmqG_Xo+9nR917TD8KmubfhyEwA2cwPA@mail.gmail.com>
Date:   Tue, 7 Feb 2023 11:53:54 -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 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.
> > > > >
> > > > > 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.

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.

> > 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.

>
>         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.

Rob