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

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Date:	Tue, 26 May 2015 16:18:42 +0100
From:	Will Deacon <will.deacon@....com>
To:	Ashwin Chaugule <ashwin.chaugule@...aro.org>
Cc:	"fu.wei@...aro.org" <fu.wei@...aro.org>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>,
	"linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"tekkamanninja@...il.com" <tekkamanninja@...il.com>,
	"graeme.gregory@...aro.org" <graeme.gregory@...aro.org>,
	"al.stone@...aro.org" <al.stone@...aro.org>,
	"hanjun.guo@...aro.org" <hanjun.guo@...aro.org>,
	"timur@...eaurora.org" <timur@...eaurora.org>,
	"arnd@...db.de" <arnd@...db.de>,
	"linux@...ck-us.net" <linux@...ck-us.net>,
	"vgandhi@...eaurora.org" <vgandhi@...eaurora.org>,
	"wim@...ana.be" <wim@...ana.be>, "jcm@...hat.com" <jcm@...hat.com>,
	"leo.duran@....com" <leo.duran@....com>,
	"corbet@....net" <corbet@....net>,
	Mark Rutland <Mark.Rutland@....com>,
	Catalin Marinas <Catalin.Marinas@....com>
Subject: Re: [PATCH v3 6/6] ACPI: import watchdog info of GTDT into platform
 device

On Tue, May 26, 2015 at 04:02:56PM +0100, Ashwin Chaugule wrote:
> On 26 May 2015 at 08:28, Will Deacon <will.deacon@....com> wrote:
> > On Mon, May 25, 2015 at 11:03:13AM +0100, fu.wei@...aro.org wrote:
> >> From: Fu Wei <fu.wei@...aro.org>
> >>
> >> 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@....com>
> >> Tested-by: Timur Tabi <timur@...eaurora.org>
> >> Signed-off-by: Fu Wei <fu.wei@...aro.org>
> >> ---
> >>  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 system’s 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:
> • Secure privilege level 1 (EL1) timer,
> • Non-Secure EL1 timer,
> • Non-Secure privilege level 2 (EL2) timer,
> • Virtual timer,
> and the following Platform (memory-mapped) timers.
> • GT Block
> • 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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