Re: [PATCH 04/15] ARM: smp_twd: add device tree support

[Marc Zyngier <marc.zyngier@arm.com>]

On 12/01/12 16:27, Rob Herring wrote:
> Adding devicetree-discuss since we are talking bindings...
> 
> On 01/12/2012 10:00 AM, Marc Zyngier wrote:
>> On 12/01/12 15:42, Rob Herring wrote:
>>> On 01/12/2012 08:36 AM, Marc Zyngier wrote:
>>>> Hi Rob,
>>>>
>>>> On 11/01/12 21:05, Rob Herring wrote:
>>>>> On 01/11/2012 07:08 AM, Marc Zyngier wrote:
>>>>>> Add bindings to support DT discovery of the ARM Timer Watchdog
>>>>>> (aka TWD). Only the timer side is converted by this patch.
>>>>>>
>>>>>> Cc: Rob Herring <rob.herring@calxeda.com>
>>>>>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>>>>>> ---
>>>>>>  Documentation/devicetree/bindings/arm/twd.txt |   29 +++++++++++
>>>>>>  arch/arm/include/asm/smp_twd.h                |    1 +
>>>>>>  arch/arm/kernel/smp_twd.c                     |   68 ++++++++++++++++++++-----
>>>>>>  3 files changed, 85 insertions(+), 13 deletions(-)
>>>>>>  create mode 100644 Documentation/devicetree/bindings/arm/twd.txt
>>>>>>
>>>>>> diff --git a/Documentation/devicetree/bindings/arm/twd.txt b/Documentation/devicetree/bindings/arm/twd.txt
>>>>>> new file mode 100644
>>>>>> index 0000000..a9d5587
>>>>>> --- /dev/null
>>>>>> +++ b/Documentation/devicetree/bindings/arm/twd.txt
>>>>>> @@ -0,0 +1,29 @@
>>>>>> +* ARM Timer Watchdog
>>>>>> +
>>>>>> +ARM 11MP, Cortex-A5 and Cortex-A9 are often associated with a per-core
>>>>>> +Timer-Watchdog (aka TWD), which provides both a per-cpu local timer
>>>>>> +and watchdog.
>>>>>> +
>>>>>> +The TWD is usually attached to a GIC to deliver its two per-processor
>>>>>> +interrupts.
>>>>>> +
>>>>>> +Main node required properties:
>>>>>> +
>>>>>> +- compatible : Should be one of:
>>>>>> +	"arm,cortex-a9-twd"
>>>>>> +	"arm,cortex-a5-twd"
>>>>>> +	"arm,arm11mp-twd"
>>>>>> +	"arm,smp-twd"
>>>>>> +
>>>>>> +- interrupts : Two interrupts to each core, the first one for the
>>>>>> +  timer, the second one for the watchdog.
>>>>>> +
>>>>>> +- reg : Specify the base address and the size of the TWD.
>>>>>> +
>>>>>> +Example:
>>>>>> +
>>>>>> +	twd@2c000600 {
>>>>>> +		compatible = "arm,arm11mp-twd", "arm,smp-twd";
>>>>>> +		reg = <0x2c000600 0x100>;
>>>>>> +		interrupts = <1 13 0xf01 1 14 0xf01>;
>>>>>> +	};
>>>>>
>>>>> Why not split the watchdog and timer into 2 nodes? It may not matter
>>>>> since there is no driver for the timer. If there was, we would have a
>>>>> problem as you can't match 2 drivers to 1 node.
>>>>
>>>> Don't we hit the opposite problem - two nodes with the same address?
>>>
>>> No, because the timer is at 0x600-0x61f and the watchdog is at
>>> 0x620-0x63f. There's no DT requirement on address range start or size.
>>>
>>> However, the current watchdog driver includes 0x20 in its register
>>> offsets, so changing the base address would require a change to the
>>> driver (but that shouldn't really influence the decision).
>>
>> Well, that's what triggered my question. On the other hand, I do not see
>> any in-tree user of the mpcore_wdt driver, so I suppose we could change
>> this register offset without too much harm.
>>
>> How about something like:
>>
>> 	twd-timer@2c000600 {
>> 		compatible = "arm,arm11mp-twd", "arm,smp-twd";
>> 		reg = <0x2c000600 0x20>;
>> 		interrupts = <1 13 0xf01>;
>> 	};
>>
>> 	twd-watchdog@2c000620 {
>> 		compatible = "arm,arm11mp-wd", "arm,smp-wd";
>> 		reg = <0x2c000620 0x20>;
>> 		interrupts = <1 14 0xf01>;
> 
> BTW, are these really edge triggered?

Yes (on the 11MPcore):
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0360f/CCHFHDJH.html

Other cores may be configured differently (A9 has some PPIs configured
as level-low, and others configured edge-rising):
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0407g/CCHEIGIC.html

All that is probably very SoC specific anyway.

> 
>> 	};
>>
>> I'm not sure about the compatible strings for the watchdog though. Any
>> better idea?
> 
> Some reason I did arm,smp-twd and arm-cortex-a9-wdt for highbank.dts
> which wasn't very consistent.
> 
> How about *-twd-timer and *-twd-wdt?

Fine by me.

> Probably we should drop the generic "arm-smp-*" versions.

Agreed. I'll respin this patch series and add the necessary updates to
the affected platforms' DTS.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...