linux-kernel - Re: [PATCH v2 1/4] mfd: add LM3533 lighting-power core driver

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Message-ID: <20120503165437.GF15752@localhost>
Date:	Thu, 3 May 2012 18:54:37 +0200
From:	Johan Hovold <jhovold@...il.com>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc:	Rob Landley <rob@...dley.net>, Richard Purdie <rpurdie@...ys.net>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Jonathan Cameron <jic23@....ac.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	Arnd Bergmann <arnd@...db.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-iio@...r.kernel.org, devel@...verdev.osuosl.org,
	linux-fbdev@...r.kernel.org
Subject: Re: [PATCH v2 1/4] mfd: add LM3533 lighting-power core driver

On Thu, May 03, 2012 at 04:24:07PM +0100, Mark Brown wrote:
> On Thu, May 03, 2012 at 05:00:40PM +0200, Johan Hovold wrote:
> > On Thu, May 03, 2012 at 12:38:02PM +0100, Mark Brown wrote:
> 
> > > This is one of the reasons why we currently use tracepoints (they just
> > > don't have this issue as they're trivial to filter), though
> > > adding some sort of infrastructure for it ought not to be too difficult
> > > even if it's just at the regmap level.
> 
> > So a /sys/kernel/debug/regmap/<device>/io_printk attribute (with a
> > better name) to enable debug printks in io paths
> > (regmap*{read,write,update} outside of mutex) in regmap.c would be
> > acceptable?
> 
> Yes, that'd be totally fine for me - it's debugfs so we can always drop
> it later if someone comes up with a better idea or something.

Ok. I'll have a look at this next week (will be on the road for a few
days), and drop the dev_dbg from the lm3533 io-functions for now.

> > > Actually, the other question I had but forgot to ask (or I think punted
> > > on for your response) was why these are in sysfs at all - things like
> > > which things are connected to the backlight are going to be a property
> > > of the board design so should be defined by the machine not tweaked from
> > > userspace.
> 
> > I agree with you and the reason is the same as for the max_current
> > attribute (discussed in the other thread) -- it was an explicit request
> > from the end customer.
> 
> > I could replace the boost attributes with a platform_data entry where it
> > really belongs.
> 
> I really think this is much better for mainline.

Agreed.

> > There is a use case (beyond testing/integration) for keeping the (lvled)
> > outputs configurable from userspace, in that it provides a way to
> > synchronise LED activity such as blinking. So I still want to keep those,
> > at least for the lvleds.
> 
> I'm not sure exactly which control that is?

That would be the output_lvled[n] (n = 1..5) attributes. For example, to
have all five low-voltage sinks blink synchronously, you could assign 0
to all these five attributes, and set a timer trigger for the led device
which has id 0.

Thanks,
Johan
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