Re: [Xen-devel] [PATCH v2] arm/gic-v3: Fix ACPI probe fail on GICv4 hardware

[Julien Grall <julien.grall@xxxxxxx>]

Hello Shanker,

On 27/05/16 16:30, Shanker Donthineni wrote:
> On 05/27/2016 10:10 AM, Julien Grall wrote:
> > On 27/05/16 16:00, Shanker Donthineni wrote:
> > > The current driver ACPI probe fails on hardware which has GICv4
> > > version, even though it is fully compatible to GICv3. This patch
> > > fixes the issue by registering the same probe function for GICv4
> > > hardware.
> > >
> > > Signed-off-by: Shanker Donthineni <shankerd@xxxxxxxxxxxxxx>
> > > ---
> > > Changes since v1:
> > >      - Edit commit text.
> > >      - Fix BUG() in xen/arch/arm/domain.c
> > Please see my latest comment on the previous version [1].
> >
> > To go further, the ACPI tables may not represent the actual hardware. It is 
> > possible to have ACPI tables describing a GICv2 whilst the real hardware is a 
> > GICv3.
> Yes, it is absolutely valid and UEFI firmware can decide what to be exported to 
> OS by changing the version number in ACPI MADT table.
>
> On Qualcomm Technologies QDF2XXX platforms, GIC version set to 4.
To be clear, I am not against adding support of GICv4 in Xen. My concern 
is how the patch add it. Exposing GICv4 beyond the GICv3 driver is not 
necessary today.
Better to keep as small as possible until we figure out how Xen will 
support GICv4 features.
I.e, the following the code should be enough.

ACPI_DEVICE_START(acgicv4, "GICv4", DEVICE_GIC)
   .class_type = ACPI_MADT_GIC_VERSION_V4,
   .init = gicv3_acpi_preinit,
ACPI_DEVICE_END

> > Xen will use the GICv2 driver and not the GICv3. So the helper will return 
> > GIC_V2 (and not GIC_V3).
> The current xen is supporting both the GICv2 and GICv3 for ACPI based boot.
>
> ACPI_DEVICE_START(agicv3, "GICv3", DEVICE_GIC)
>          .class_type = ACPI_MADT_GIC_VERSION_V3,
>          .init = gicv3_acpi_preinit,
> ACPI_DEVICE_END
>
> ACPI_DEVICE_START(agicv2, "GICv2", DEVICE_GIC)
>          .class_type = ACPI_MADT_GIC_VERSION_V2,
>          .init = gicv2_acpi_preinit,
> ACPI_DEVICE_END
Regards,

--
Julien Grall

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