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

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Date:   Wed, 28 Sep 2016 09:12:03 -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> [160928 08:29]:
> 
> > Am 28.09.2016 um 17:12 schrieb Tony Lindgren <tony@...mide.com>:
> > 
> > * 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?
> 
> It is a matter of taste and something not easy to decide...
> 
> And everything can be changed from user-space by some script
> running during the boot process to a more meaningful setting.
> 
> So the initial setting doesn't matter really much.
> 
> Having some of the LEDs as heartbeat gives an (additional)
> feedback that the kernel has booted.
> 
> We could even take led1, led3 and led5 as heartbeat and the other
> two as default-on. Would give a nice pattern showing that the LEDs
> are not broken...
> 
> So let me know how you would like to have it and I add it to a PATCH v2.

Up to you for the blinking, I'm fine with the original version
too unless you feel like changing it.

Regards,

Tony