XO-1.5 disk activity light doesn't work

[wad]

On an XO-1.5, the disk activity LED is wired to GPIO11. The LED will light when the GPIO line is driven low.

At this time, there is no software to blink this LED when disk activity is occuring.

[Quozl]

Should the LED blink on read, write, or both?

[dsaxena]

Looked into this and the kernel has an LED subsystem that can be used to hook this in. Like most kernel stuff, documentation is rather lacking but what I believe we need to do is:

- Add a mmcblock LED trigger event (maybe we can piggyback on the existing IDE disk trigger?) - Add a driver for the XO that ties into this trigger (There's an existing GPIO LED driver, might be able to hook into it..)

[Quozl]

I agree the kernel LED subsystem is probably a nicer place to do this rather than hacking in GPIO manipulation into the mmc/card/block.c ... I've thought about human interface and usability a bit more ... and came up with an alternate semantics:

• short flashes for reads in the absence of writes,
• long flashes for writes,
• constant on for a long write queue,

There's also some really neat functionality lurking in the LED driver that someone might like to consider for power limited deployments ... for example expressing the battery drain current using the heartbeat LED trigger, which currently is based on 1min load average (led_heartbeat* in drivers/leds/ledtrig-heartbeat.c) ... by giving immediate feedback of power consumption the child will learn how to optimise their running time.

[Quozl]

Related: Q3A60 and later flashes the disk activity light during fs-update.

[pgf]

jnettlet has made this work on 1.75. presumably applying the changes to 1.5 would be straightforward.

from the arm-3.0-wip branch:

9d27e83 xo_175_defconfig: Add default LED options
5191223 olpc: hookup mmc block trigger to storage led
dcabbb3 leds: Add MMC Block Trigger
abbd9b2 olpc: hook up the storage led

[jnettlet]

MMC Block Trigger

[jnettlet]

XO 1.5 storage led platform device patch

[jnettlet]

These can be reviewed and merged whenever.