linux-kernel - Re: [PATCH 2/3] DT: EVM: add LEDs

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Message-ID: <20160928151234.c3x36lhnvk4potdy@atomide.com>
Date:   Wed, 28 Sep 2016 08:12:35 -0700
From:   Tony Lindgren <tony@...mide.com>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
Cc:     Benoît Cousson <bcousson@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        linux-omap@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, letux-kernel@...nphoenux.org
Subject: Re: [PATCH 2/3] DT: EVM: add LEDs

* H. Nikolaus Schaller <hns@...delico.com> [160927 23:50]:
> Hi,
> 
> > Am 28.09.2016 um 05:37 schrieb Tony Lindgren <tony@...mide.com>:
> > 
> > * H. Nikolaus Schaller <hns@...delico.com> [160927 13:11]:
> >>> Am 27.09.2016 um 21:49 schrieb Tony Lindgren <tony@...mide.com>:
> >>> How about this for defaults:
> >>> 
> >>> - heartbeat for led3
> >>> - cpu0 for led4
> >>> - cpu1 for led5
> >> 
> >> Good idea. Will try.
> >> 
> >> What I don't exactly know is if these gpios based on an I2C-expander
> >> can handle cpu activity triggers or if they are locked up if this i2c
> >> processing triggers another cpu activity...
> > 
> > Oh right, if the GPIOs are on the i2c bus
> 
> yes, they are all gpio9 which is the tca6424 on i2c5.
> 
> > it's probably not a good
> > idea :) Or at least will be inaccurate if the bus can sleep.
> 
> I have tested a little by writing to /sys/class/leds/.../trigger.
> 
> If I make one LED trigger by "cpu0" it is always on and if I make
> a second one triggered by "cpu1" the heartbeat becomes irregular.
> 
> So indeed this does not work.

So should we just leave the default trigger unpopulated then?

Regards,

Tony