[RFC 2/8] ARM:global_timer: Add ARM global timer support.

From: srinivas.kandagatla@st•com (Srinivas KANDAGATLA)
To: linux-arm-kernel@lists•infradead.org
Subject: [RFC 2/8] ARM:global_timer: Add ARM global timer support.
Date: Thu, 09 May 2013 15:07:59 +0100	[thread overview]
Message-ID: <518BADBF.4070303@st.com> (raw)
In-Reply-To: <201305081638.23100.arnd@arndb.de>

On 08/05/13 15:38, Arnd Bergmann wrote:
> On Wednesday 08 May 2013, Srinivas KANDAGATLA wrote:
>> From: Stuart Menefy <stuart.menefy@st•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@st•com>
>> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@st•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.

Yes, in mainline we do not have support to this.

> 
>>  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?

Sure, I will move this in the next version.

>  
>> 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.

sorry Am confused here.
How would this work for non-DT?

Looking at the code in clocksource_of_init it just goes through the
of_device_id table, which is not used in case of non-DT.
> 
> 	Arnd
> 
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