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Date: Thu, 15 Sep 2016 16:47:36 +0100
From: Mark Rutland <mark.rutland@arm.com>
To: "Bryan O'Donoghue" <pure.logic@nexus-software.ie>
Cc: Greg KH <gregkh@linuxfoundation.org>, Arnd Bergmann <arnd@arndb.de>,
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Subject: Re: [GIT PULL] Greybus driver subsystem for 4.9-rc1
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On Thu, Sep 15, 2016 at 04:40:00PM +0100, Bryan O'Donoghue wrote:
> On Thu, 2016-09-15 at 13:46 +0100, Mark Rutland wrote:
> > On Thu, Sep 15, 2016 at 12:48:08PM +0100, Bryan O'Donoghue wrote:
> > > On Thu, 2016-09-15 at 12:20 +0100, Mark Rutland wrote:
> > > > For example, you have absolutely no guarantee as to what backs
> > > > get_cycles(). Despite this, the code assumes that get_cycles() is
> > > > backed by something running at the frequency described in a
> > > > "google,greybus-frame-time-counter" node.
> > > > 
> > > > Even if this *happens* to match what some piece of arch code
> > > > provides
> > > > today on some platform, it is in no way *guaranteed*.
> > > That's the point though, if you declare "google,greybus-frame-time-
> > > counter" in your platform code - then you can use 'get_cycles()' in
> > > this manner
> > To be clear, *some* properties (and perhaps additional nodes) may
> > need
> > to be in the DT, in order to capture the hardware property or
> > relationship that you are reliant upon.
> 
> Sure but on the relevant platform we know 
> 
> 1. get_cycles() is derived from an architectured MMIO timer
> 2. What is clocking that timer
> 
> So any platform that declares that property must be aware of what its
> doing.

I can't say this any more explicitly:

****************************************************
* The DT *cannot* know anything about get_cycles() *
****************************************************

It's no more complex than that.

Thanks,
Mark.