Re: [GIT PULL] Greybus driver subsystem for 4.9-rc1

From	Mark Rutland <mark.rutland@arm.com>
Newsgroups	linux.kernel
Subject	Re: [GIT PULL] Greybus driver subsystem for 4.9-rc1
Date	2016-09-15 14:50 +0200
Message-ID	<shEh4-75Z-33@gated-at.bofh.it> (permalink)
References	(4 earlier) <shBjb-5el-1@gated-at.bofh.it> <shBVU-5HB-31@gated-at.bofh.it> <shCff-5Oi-27@gated-at.bofh.it> <shD1D-6kV-11@gated-at.bofh.it> <shDl0-6rX-19@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

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.

However, the DT cannot possibly know anything about get_cycles(), as
get_cycles() is a kernel implementation details that's subject to
arbitrary change at any point in time, independent of the DT.

The "google,greybus-frame-time-counter" node, as it stands, does not
capture any relevant hardware detail, and does not belong in the DT.

> > Without a higher-level view of what you're trying to achieve, it's
> > not clear to me whether get_cycles() is the right interface.
> 
> I appreciate that.

Until that's clarified, we won't make any progress here.

Thanks,
Mark.

Thread

Re: [GIT PULL] Greybus driver subsystem for 4.9-rc1 Mark Rutland <mark.rutland@arm.com> - 2016-09-14 19:40 +0200
  Re: [GIT PULL] Greybus driver subsystem for 4.9-rc1 Greg KH <gregkh@linuxfoundation.org> - 2016-09-14 20:10 +0200
    Re: [GIT PULL] Greybus driver subsystem for 4.9-rc1 Joe Perches <joe@perches.com> - 2016-09-14 21:10 +0200
    Re: [GIT PULL] Greybus driver subsystem for 4.9-rc1 Rob Herring <robh@kernel.org> - 2016-09-14 22:10 +0200
      Re: [GIT PULL] Greybus driver subsystem for 4.9-rc1 Greg KH <gregkh@linuxfoundation.org> - 2016-09-15 12:20 +0200
        Re: [GIT PULL] Greybus driver subsystem for 4.9-rc1 Bryan O'Donoghue <pure.logic@nexus-software.ie> - 2016-09-15 13:00 +0200
    Re: [GIT PULL] Greybus driver subsystem for 4.9-rc1 Bryan O'Donoghue <pure.logic@nexus-software.ie> - 2016-09-15 11:40 +0200
      Re: [GIT PULL] Greybus driver subsystem for 4.9-rc1 Mark Rutland <mark.rutland@arm.com> - 2016-09-15 12:20 +0200
        Re: [GIT PULL] Greybus driver subsystem for 4.9-rc1 Bryan O'Donoghue <pure.logic@nexus-software.ie> - 2016-09-15 12:40 +0200
          Re: [GIT PULL] Greybus driver subsystem for 4.9-rc1 Bryan O'Donoghue <pure.logic@nexus-software.ie> - 2016-09-15 12:50 +0200
          Re: [GIT PULL] Greybus driver subsystem for 4.9-rc1 Mark Rutland <mark.rutland@arm.com> - 2016-09-15 13:30 +0200
            Re: [GIT PULL] Greybus driver subsystem for 4.9-rc1 Bryan O'Donoghue <pure.logic@nexus-software.ie> - 2016-09-15 13:50 +0200
              Re: [GIT PULL] Greybus driver subsystem for 4.9-rc1 Mark Rutland <mark.rutland@arm.com> - 2016-09-15 14:50 +0200
                Re: [GIT PULL] Greybus driver subsystem for 4.9-rc1 Bryan O'Donoghue <pure.logic@nexus-software.ie> - 2016-09-15 17:40 +0200
                Re: [GIT PULL] Greybus driver subsystem for 4.9-rc1 Mark Rutland <mark.rutland@arm.com> - 2016-09-15 17:50 +0200
                Re: [GIT PULL] Greybus driver subsystem for 4.9-rc1 Bryan O'Donoghue <pure.logic@nexus-software.ie> - 2016-09-15 18:10 +0200

csiph-web