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

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Message-ID: <1473932133.10230.25.camel@nexus-software.ie>
Date:   Thu, 15 Sep 2016 10:35:33 +0100
From:   Bryan O'Donoghue <pure.logic@...us-software.ie>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Mark Rutland <mark.rutland@....com>
Cc:     Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
        Johan Hovold <johan@...oldconsulting.com>,
        Rui Miguel Silva <rmfrfs@...il.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Sandeep Patil <sspatil@...gle.com>,
        Matt Porter <mporter@...nel.crashing.org>,
        John Stultz <john.stultz@...aro.org>,
        Rob Herring <robh@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Alex Elder <elder@...aro.org>, David Lin <dtwlin@...gle.com>,
        Vaibhav Agarwal <vaibhav.agarwal@...aro.org>,
        Mark Greer <mgreer@...malcreek.com>, marc.zyngier@....com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [GIT PULL] Greybus driver subsystem for 4.9-rc1

On Wed, 2016-09-14 at 20:29 +0200, Greg KH wrote:
> On Wed, Sep 14, 2016 at 08:07:54PM +0200, Greg KH wrote:
> > 
> > On Wed, Sep 14, 2016 at 06:36:26PM +0100, Mark Rutland wrote:
> > > 
> > > Hi Greg,
> > > 
> > > On Wed, Sep 14, 2016 at 12:09:49PM +0200, Greg KH wrote:
> > > > 
> > > > Given that it's never a good idea to keep subsystems out of the
> > > > mainline
> > > > kernel, I've put together this pull request that adds the
> > > > greybus driver
> > > > layer to drivers/greybus/.  Because this was 2 1/2 years of
> > > > work, with
> > > > many many developers contributing, I didn't want to flatten all
> > > > of their
> > > > effort into a few small patches, as that wouldn't be very
> > > > fair.  So I've
> > > > built a git tree with all of the changes going back to the
> > > > first commit,
> > > > and merged it into the kernel tree, just like btrfs was merged
> > > > into the
> > > > kernel.
> > > > 
> > > > Unless people point out some major problems with this, I'd like
> > > > to get
> > > > it merged into 4.9-rc1.
> > > I'm extremely concerned that these patches have *never* seen
> > > upstream
> > > review, and this pull request gives no real opportunity for
> > > people to
> > > make a judgement regarding the code, as many relevant parties
> > > have not
> > > been Cc'd.
> > As I said, I will send a set of simple patches, I wanted to get
> > this out
> > as soon as possible and other things came up today.  Will do it in
> > the
> > morning, sorry.
> Here's the timesync code pulled out into a simple patch if you want
> to
> see it.
> 
> Bryan, any explanations you want to provide that would help in
> clarifying Mark's issues?

As Douglas Adams would say - "don't panic".

If you look at the final state the code ends up in - we're doing
get_cycles(); as opposed to reading an architectural timer directly.

u64 gb_timesync_platform_get_counter(void)
{
        return (u64)get_cycles();
}

You have the entire git history - from the early days where we were reading one of the unused ARMv8 timers the MSM8994 has to the later days where we just do get_cycles()...

At the time when we first started writing the code it wasn't 100% clear if get_cycles() would do, so it was safer to allocate an unused architectural timer and read it directly. Later on and with some experimentation it was possible to switch to get_cycles().

---
bod