linux-kernel - Re: [RFC 2/8] ARM:global_timer: Add ARM global timer support.

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Message-Id: <201305081638.23100.arnd@arndb.de>
Date:	Wed, 8 May 2013 16:38:22 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Srinivas KANDAGATLA <srinivas.kandagatla@...com>
Cc:	linux@....linux.org.uk, will.deacon@....com,
	Rob Landley <rob@...dley.net>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Stuart Menefy <stuart.menefy@...com>,
	Shawn Guo <shawn.guo@...aro.org>,
	Olof Johansson <olof@...om.net>,
	Jason Cooper <jason@...edaemon.net>,
	Stephen Warren <swarren@...dia.com>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Nicolas Pitre <nico@...aro.org>,
	Dave Martin <dave.martin@...aro.org>,
	Marc Zyngier <marc.zyngier@....com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Dong Aisheng <dong.aisheng@...aro.org>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org,
	linux-arm-kernel@...ts.infradead.org, linux-serial@...r.kernel.org
Subject: Re: [RFC 2/8] ARM:global_timer: Add ARM global timer support.

On Wednesday 08 May 2013, Srinivas KANDAGATLA wrote:
> From: Stuart Menefy <stuart.menefy@...com>
> 
> This is a simple driver for the global timer module found in the Cortex
> A9-MP cores from revision r1p0 onwards. This should be able to perform
> the functions of the system timer and the local timer in an SMP system.
> 
> The global timer has the following features:
>     The global timer is a 64-bit incrementing counter with an
> auto-incrementing feature. It continues incrementing after sending
> interrupts. The global timer is memory mapped in the private memory
> region.
>     The global timer is accessible to all Cortex-A9 processors in the
> cluster. Each Cortex-A9 processor has a private 64-bit comparator that
> is used to assert a private interrupt when the global timer has reached
> the comparator value. All the Cortex-A9 processors in a design use the
> banked ID, ID27, for this interrupt. ID27 is sent to the Interrupt
> Controller as a Private Peripheral Interrupt. The global timer is
> clocked by PERIPHCLK.
> 
> Signed-off-by: Stuart Menefy <stuart.menefy@...com>
> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@...com>
>

Are you sure we don't already have a driver for this? It sounds unlikely
that you are the first one to do this when the hardware is so common.

>  Documentation/devicetree/bindings/arm/gt.txt |   21 ++
>  arch/arm/Kconfig                             |    6 +
>  arch/arm/include/asm/global_timer.h          |   12 +
>  arch/arm/kernel/Makefile                     |    1 +
>  arch/arm/kernel/global_timer.c               |  325 ++++++++++++++++++++++++++
>  5 files changed, 365 insertions(+), 0 deletions(-)
>  create mode 100644 Documentation/devicetree/bindings/arm/gt.txt
>  create mode 100644 arch/arm/include/asm/global_timer.h
>  create mode 100644 arch/arm/kernel/global_timer.c

Move it into drivers/clocksource?
 
> diff --git a/arch/arm/include/asm/global_timer.h b/arch/arm/include/asm/global_timer.h
> new file mode 100644
> index 0000000..46f9188
> --- /dev/null
> +++ b/arch/arm/include/asm/global_timer.h
> @@ -0,0 +1,12 @@
> +int __init global_timer_init(void __iomem *base, unsigned int timer_irq);

I don't see a need to call this from platform code for non-DT platforms, it
can easily be used with CLOCKSOURCE_OF_DECLARE() all the time I think.

	Arnd
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