From:   "Michael Kelley (LINUX)" <mikelley@microsoft.com>
To:     Saurabh Singh Sengar <ssengar@linux.microsoft.com>
CC:     "robh+dt@kernel.org" <robh+dt@kernel.org>,
        "krzysztof.kozlowski+dt@linaro.org" 
        <krzysztof.kozlowski+dt@linaro.org>,
        KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        "wei.liu@kernel.org" <wei.liu@kernel.org>,
        Dexuan Cui <decui@microsoft.com>,
        "daniel.lezcano@linaro.org" <daniel.lezcano@linaro.org>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "lenb@kernel.org" <lenb@kernel.org>,
        "rafael@kernel.org" <rafael@kernel.org>,
        "linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>
Subject: RE: [PATCH v7 5/5] Driver: VMBus: Add Devicetree support
Thread-Topic: [PATCH v7 5/5] Driver: VMBus: Add Devicetree support
Thread-Index: AQHZR3oO8XCRAJVOTEyd9eleCYLxd674F9KAgAA/zYCAAGYrcA==
Date:   Mon, 13 Mar 2023 12:26:56 +0000
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From: Saurabh Singh Sengar <ssengar@linux.microsoft.com> Sent: Sunday, Marc=
h 12, 2023 11:16 PM
>=20
> On Mon, Mar 13, 2023 at 02:33:53AM +0000, Michael Kelley (LINUX) wrote:
> > From: Saurabh Sengar <ssengar@linux.microsoft.com> Sent: Thursday, Febr=
uary 23,
> 2023 3:29 AM
> > >
> > > Update the driver to support Devicetree boot as well along with ACPI.
> > > At present the Devicetree parsing only provides the mmio region info
> > > and is not the exact copy of ACPI parsing. This is sufficient to cate=
r
> > > all the current Devicetree usecases for VMBus.
> > >
> > > Currently Devicetree is supported only for x86 systems.
> > >
> > > Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
> > > ---
> > > [V7]
> > > - Use cpu_addr instead of bus_addr
> > >
> > >  drivers/hv/Kconfig     |  6 +++--
> > >  drivers/hv/vmbus_drv.c | 57 ++++++++++++++++++++++++++++++++++++++++=
--
> > >  2 files changed, 59 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
> > > index 0747a8f1fcee..1a55bf32d195 100644
> > > --- a/drivers/hv/Kconfig
> > > +++ b/drivers/hv/Kconfig
> > > @@ -4,11 +4,13 @@ menu "Microsoft Hyper-V guest support"
> > >
> > >  config HYPERV
> > >  	tristate "Microsoft Hyper-V client drivers"
> > > -	depends on ACPI && ((X86 && X86_LOCAL_APIC && HYPERVISOR_GUEST) \
> > > -		|| (ARM64 && !CPU_BIG_ENDIAN))
> > > +	depends on (X86 && X86_LOCAL_APIC && HYPERVISOR_GUEST) \
> > > +		|| (ACPI && ARM64 && !CPU_BIG_ENDIAN)
> > >  	select PARAVIRT
> > >  	select X86_HV_CALLBACK_VECTOR if X86
> > >  	select VMAP_PFN
> > > +	select OF if !ACPI
> > > +	select OF_EARLY_FLATTREE if !ACPI
> > >  	help
> > >  	  Select this option to run Linux as a Hyper-V client operating
> > >  	  system.
> >
> > One further thing occurred to me.  OF_EARLY_FLATTREE really depends
> > on OF instead of ACPI.   The ACPI dependency is indirect through OF.  S=
o
> > I'd suggest doing
> >
> > 	select OF_EARLY_FLATTRE if OF
> >
> > to express the direct dependency.
>=20
> As you pointed out OF_EARLY_FLATTRE is anyway dependent on OF, and thus I
> feel this check is redundant. I see all the Kconfig options which enables
> both of these flags don't explicitly mention this dependency.
>=20
> >
> > Separately, I wonder if the "select OF if !ACPI" is even needed.  It do=
esn't
> > hurt anything to leave it, but it seems like any config that doesn't
> > independently select either ACPI or OF is broken for reasons unrelated
> > to Hyper-V.  I'm OK with leaving the select of OF if you want, so I'm
> > more just wondering than asserting it should be removed.   I didn't
> > see "select OF if !ACPI" anywhere else in the Kconfig files, and it
> > seems like Hyper-V would not be the only environment where this
> > is the expectation.
>=20
> Ok I can remove the !ACPI dependency. Hope kernel size increase due to bo=
th
> the code compiled in shouldn't be problem for ACPI systems.
> And here if config doesn't select ACPI or OF it will assume OF, which is
> better then selecting none of them.
>=20
>=20
> To address both of your comments I feel below will be sufficient:
> select OF
> select OF_EARLY_FLATTRE

Actually, that's not what I was thinking. :-)   I was thinking for the Hype=
r-V
Kconfig to be silent on selecting OF, just like it is silent on selecting A=
CPI.
Whoever is configuring the kernel build would separately be selecting
ACPI, or OF, or both, depending on their needs.   I don't think the Hyper-V
Kconfig should always be selecting OF, because of the reason you noted --
it drags in code that is not needed for normal VTL 0 usage.  If you take
that approach, then

	select OF_EARLY_FLATTREE if OF

is appropriate.

Michael


>=20
>=20
> Regards,
> Saurabh
>=20
> >
> > Michael