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

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Message-Id: <6004B143-F64B-4DA9-A054-3F2AB3FC2346@goldelico.com>
Date:   Wed, 28 Sep 2016 08:49:30 +0200
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Tony Lindgren <tony@...mide.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

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.

BR,
Nikolaus