linux-kernel - Re: [PATCH v2 02/18] dt-bindings: timer: sp804: add timer-width property

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Date:	Thu, 17 Mar 2016 19:21:23 +0000
From:	Robin Murphy <robin.murphy@....com>
To:	Rob Herring <robh@...nel.org>
Cc:	Neil Armstrong <narmstrong@...libre.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Sudeep Holla <sudeep.holla@....com>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 02/18] dt-bindings: timer: sp804: add timer-width
 property

On 17/03/16 19:00, Rob Herring wrote:
> On Thu, Mar 17, 2016 at 1:06 PM, Robin Murphy <robin.murphy@....com> wrote:
>> Hi Rob,
>>
>> On 17/03/16 17:09, Rob Herring wrote:
>>>
>>> On Wed, Mar 09, 2016 at 11:24:04AM +0100, Neil Armstrong wrote:
>>>>
>>>> Add timer-width optional property to specify a different vendor
>>>> specific timer counter bit-width.
>>>>
>>>> Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
>>>> ---
>>>>    Documentation/devicetree/bindings/timer/arm,sp804.txt | 2 ++
>>>>    1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/timer/arm,sp804.txt
>>>> b/Documentation/devicetree/bindings/timer/arm,sp804.txt
>>>> index 5cd8eee7..141e143 100644
>>>> --- a/Documentation/devicetree/bindings/timer/arm,sp804.txt
>>>> +++ b/Documentation/devicetree/bindings/timer/arm,sp804.txt
>>>> @@ -17,6 +17,8 @@ Optional properties:
>>>>    - arm,sp804-has-irq = <#>: In the case of only 1 timer irq line
>>>> connected, this
>>>>          specifies if the irq connection is for timer 1 or timer 2. A
>>>> value of 1
>>>>          or 2 should be used.
>>>> +- arm,timer-width: Should contain the width in number of bits of the
>>>> counter,
>>>> +       is considered by default 32 but can be changed for vendor
>>>> variants.
>>>
>>>
>>> That would not be an SP804 nor would the vendor be ARM in that case. So
>>> add a new compatible string for the vendor that decided to hack up ARM's
>>> IP block.
>>
>>
>> By all accounts this is some ancient reference design[1] which later evolved
>> _into_ the SP804, so that vendor would probably still be ARM ;)
>
> Right.
>
>> A separate compatible string would indeed make more sense, though. Both
>> semantically and in terms of letting the driver account for the differences
>> automatically.
>>
>> Robin.
>>
>> [1]:http://infocenter.arm.com/help/topic/com.arm.doc.ddi0170a/I350250.html
>
> Humm, same as integrator timers perhaps?

Having had a quick look, what the Integrator/AP manual describes 
certainly smells like the same basic block as the "AMBA Timer" - 16 bit 
counters and the same control register layout - albeit in a mutant 
triple-timer version with a bigger offset between each register set. 
Integrator/CP, on the other hand, looks much more SP804-like.

Robin.