Re: [PATCH v3 6/6] ACPI: import watchdog info of GTDT into platform device

[Will Deacon]

On Tue, May 26, 2015 at 04:02:56PM +0100, Ashwin Chaugule wrote:
> On 26 May 2015 at 08:28, Will Deacon <will.deacon@xxxxxxx> wrote:
> > On Mon, May 25, 2015 at 11:03:13AM +0100, fu.wei@xxxxxxxxxx wrote:
> >> From: Fu Wei <fu.wei@xxxxxxxxxx>
> >>
> >> Parse SBSA Generic Watchdog Structure in GTDT table of ACPI,
> >> and create a platform device with that information.
> >> This platform device can be used by the ARM SBSA Generic
> >> Watchdog driver.
> >>
> >> Tested-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@xxxxxxx>
> >> Tested-by: Timur Tabi <timur@xxxxxxxxxxxxxx>
> >> Signed-off-by: Fu Wei <fu.wei@xxxxxxxxxx>
> >> ---
> >>  arch/arm64/kernel/acpi.c | 145 +++++++++++++++++++++++++++++++++++++++++++++++
> >>  1 file changed, 145 insertions(+)
> >
> > Why does this all need to be under arch/arm64? The GTDT really isn't
> > architecture-specific, so I'd *much* rather it was parsed in the driver code
> > itself, like we already do for the architected timer. The GIC is an
> > exception because it's in the MADT, which we need to parse in the arch code
> > to configure SMP properly.
> 
> I'm not really against refactoring the code. But the GTDT looks quite
> specific to ARM..
> 
> ---8<----
> 5.2.24 Generic Timer Description Table (GTDT)
> This section describes the format of the Generic Timer Description
> Table (GTDT), which provides
> OSPM with information about a systemâs Generic Timers configuration.
> The Generic Timer (GT) is
> a standard timer interface implemented on ARM processor-based systems.
> The GT hardware
> specification can be found at Links to ACPI-Related Documents
> (http://uefi.org/acpi) under the
> heading ARM Architecture. The GTDT provides OSPM with information
> about a system's GT
> interrupt configurations, for both per-processor timers, and platform
> (memory-mapped) timers.
> The GT specification defines the following per-processor timers:
> â Secure privilege level 1 (EL1) timer,
> â Non-Secure EL1 timer,
> â Non-Secure privilege level 2 (EL2) timer,
> â Virtual timer,
> and the following Platform (memory-mapped) timers.
> â GT Block
> â Server Base System Architecture (SBSA) Generic Watchdog
> ---8<----

Sure, the device it describes may only ever exist on ARM systems, but by
that logic then we should be moving lots of drivers back under arch/arm[64].

The ARM architecture says precisely *nothing* about ACPI, so we should
try to keep arch/arm64/kernel/acpi.c to a minimum and not shovel all sorts
of table conversion code in there for random peripherals.

Will
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