linux-kernel - RE: [PATCH 27/38] iio: pressure-core: st: Give some indication if device probing was successful

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Date:	Fri, 13 Sep 2013 20:57:51 +0000
From:	"Getz, Robin" <Robin.Getz@...log.com>
To:	Lee Jones <lee.jones@...aro.org>,
	Lars-Peter Clausen <lars@...afoo.de>
CC:	Jonathan Cameron <jic23@...nel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jic23@....ac.uk" <jic23@....ac.uk>,
	"arnd@...db.de" <arnd@...db.de>,
	"linus.walleij@...aro.org" <linus.walleij@...aro.org>,
	"denis.ciocca@...com" <denis.ciocca@...com>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>
Subject: RE: [PATCH 27/38] iio: pressure-core: st: Give some indication if
 device probing was successful

On Wednesday, September 11, 2013 3:30 AM Lee Jones wrote:
> On Wed, 11 Sep 2013, Lars-Peter Clausen wrote:
> > On 09/11/2013 09:10 AM, Lee Jones wrote:
> > >On Tue, 10 Sep 2013, Jonathan Cameron wrote:
> > >>Lee Jones <lee.jones@...aro.org> wrote:
> > Silence means everything is good, a message means there is an error.
> > If every device that gets probed would spit out a message the log
> > would be scrolling forever and you wouldn't be able to see the error
> > messages.
> 
> Only if you print out every regulator, clock, GPIO pin and things of this nature.
> Key hardware blocks such as; SD, Flash, USB, Eth, HDMI, Audio, UART, GPIO and
> I2C controllers and Sensors I think deserve a one line "I'm here and working"
> message.

In many embedded systems -- there are lots and lots of IIO devices, and I'm not sure 
I would consider very many "key". It really depends on the board.

To me it's a matter of boot time. Even memcpy to msgbuf takes time.
Sometimes unnecessary time.

> I'll not fight this for too long. This is based my experience as a user. I tried to
> look at the bootlog for the sensors I'd just enabled and there was nothing. Some
> of them had probed, some hadn't and there was no clear way to distinguish
> between them without digging into sysfs.

echo "working:"
cat /sys/bus/iio/devices/*/name

isn't too much digging. If you really want to do that on your machine - do so in rc.local

for many other subsystems, it's just not that easy, and printing from the driver is necessary.

-Robin