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

[Robin Murphy]

Hi Neil,

On 22/03/16 09:21, Neil Armstrong wrote:
> On 03/17/2016 08:21 PM, Robin Murphy wrote:
> > On 17/03/16 19:00, Rob Herring wrote:
> > > On Thu, Mar 17, 2016 at 1:06 PM, Robin Murphy <robin.murphy@xxxxxxx> wrote:
> > > > Hi Rob,
> > > >
> > > > On 17/03/16 17:09, Rob Herring wrote:
> > > > > 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.
>
> Hi,
>
> I will switch to oxsemi,ox810se-rps-timer since it need a specific register width that will be handled by the driver.

By "needs a specific register width" do you mean the OxSemi 
implementation will give a bus error on a 32-bit access and requires 
16-bit accessors? If so, I'd expect to see patch 1 changing readl()s to 
readw()s at least somewhere. Otherwise, if it's merely that the 
clocksource API needs to know the upper 16 bits of a word it reads are 
undefined, then since that's the standard behaviour I'd be inclined to 
add it to the driver as a canonical "arm,amba-timer" implementation, 
then have your implementation-specific compatible on top of that just in 
case.

Robin.

> Thanks,
> Neil
>
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