I want to know that this trigger has active users that
cannot live without it if we are to continue to support it.
We're using this feature. Our use case is a LED at the front panel which
shows whether a signal is present at an input LC optical connector (DWDM
network stuff). Here's how we're setting it up:
https://gerrit.cesnet.cz/plugins/gitiles/CzechLight/br2-external/+/6570b571bbf3f53cf24ef2be3079bc282c445b9e/package/czechlight-clearfog-leds/init-leds-edfa.sh
I understand that the GPIO numeric namespace is racy, but it's never been a
problem for us in the past 5 years since this script runs much later during
boot than any driver probing.
Option if this is really needed: I can develop a new trigger
that can associate GPIOs with LEDs as triggers using device
tree, which should also remove the use of userspace custom
scripts to achieve this and be much more trustworthy, if
someone with the Nokia n810 or a device with a similar need
is willing to test it.
I'll be happy to test a patch like that.
However, the GPIO in question on our board is connected to a MCP23S18, and
we have a pair of these. When used in this configuration (two chips at the
same SPI CS, differing by a chip-specific "HW address" on a HW level),
there are some impedance mismatches because it's essentially two
independent pinctrl instances on the same SPI address. This causes
problems, e.g. the debugfs pinctrl instance won't be created for the second
chip because of a naming conflict. We also carry this out-of-tree patch to
make the GPIO labels work when set from DTS:
https://patchwork.ozlabs.org/project/linux-gpio/patch/517dcdda21ea0b0df884bc6adcba1dadb78b66b1.1551966077.git.jan.kundrat@xxxxxxxxx/
(Feedback on how to solve that problem is welcome, btw.)
Since I am not that much familiar with pinctrl/gpio stuff in kernel, I
wanted to bring this up to make sure that your future trigger works even on
a setup like ours. Here's how it's used via DTS in case it's relevant:
https://gerrit.cesnet.cz/plugins/gitiles/CzechLight/br2-external/+/6570b571bbf3f53cf24ef2be3079bc282c445b9e/board/czechlight/clearfog/sdn-roadm-clearfog.dtsi#151
With kind regards,
Jan
