linux-kernel - Re: [RFC/PATCH 11/11] arm: boot: dts: omap: add missing default status for 32k counter

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Date:	Mon, 5 Oct 2015 12:52:30 -0500
From:	Felipe Balbi <balbi@...com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	<balbi@...com>, <linux-arm-kernel@...ts.infradead.org>,
	Tony Lindgren <tony@...mide.com>, <daniel.lezcano@...aro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	<tglx@...utronix.de>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>
Subject: Re: [RFC/PATCH 11/11] arm: boot: dts: omap: add missing default
 status for 32k counter

On Wed, Sep 30, 2015 at 11:58:16PM +0200, Arnd Bergmann wrote:
> On Wednesday 30 September 2015 09:12:09 Felipe Balbi wrote:
> > On Wed, Sep 30, 2015 at 10:15:25AM +0200, Arnd Bergmann wrote:
> > > On Tuesday 29 September 2015 15:44:06 Felipe Balbi wrote:
> > > > All devices should have a default status. Ignoring
> > > > the arguments if it should be 'okay' or 'disabled'
> > > > by default, let's set them all the 'disabled' and
> > > > have boards enable 32k counter.
> > > > 
> > > > Signed-off-by: Felipe Balbi <balbi@...com>
> > > > 
> > > 
> > > The patch looks good, but the description is slightly incorrect:
> > > There is no reason to list "status='okay'" other than overriding
> > > the 'disabled' status.
> > > 
> > > I'd phrase it something like:
> > > 
> > > "We want the use of the 32k counter to be a per-board setting,
> > > so let's disable it by default in each dtsi file and override the
> > > setting in the boards. Any board that does not wire up the counter
> > > should leave it disabled".
> > > 
> > > However, if you really want all boards to provide the counter all
> > > the time, I'd argue that we're better off dropping this patch. We
> > > use the status="disabled" trick for anything that may or may not
> > > be working based on the board design, but things that are present
> > > everywhere don't need this.
> > 
> > okay, so here's the thing. While fiddling with the 32k counter, I noticed
> > that even though there was no status listed, the thing still initializes
> > fine. However, when moving 32k to drivers/clocksource and using
> > CLOCKSOURCE_OF_DECLARE(), 32k would *NOT* probe unless I had an explicit
> > status = "okay" in DT.
> 
> Very strange, that sounds like a bug in the clocksource probe code.
> Can you check how this happens?

seems like something overwrites counter's status field, here's a snippet of boot
log:

[    0.000000] ===> counter is available ??
[    0.000000] ===> no status -> TRUE!!
[    0.000000] ===> searching for timer
[    0.000000] ===> timer is available ??
[    0.000000] ===> no status -> TRUE!!
[    0.000005] sched_clock: 64 bits at 1000MHz, resolution 1ns, wraps every 4398046511103ns
[    0.000014] clocksource: arm_global_timer: mask: 0xffffffffffffffff max_cycles: 0x1cd42e4dffb, max_idle_ns: 881590591483 ns
[    0.000047] ===> searching for timer
[    0.000051] ===> timer is available ??
[    0.000054] ===> no status -> TRUE!!
[    0.000307] ===> searching for counter
[    0.000311] ===> counter is available ??
[    0.000315] ===> counter status disabled
[    0.000318] ====> counter NOT available

note that first time around counter had no status and later it got a status
disabled from somewhere.

-- 
balbi

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