rt2x00: LED classes

rt2x00: LED classes

[Ivo van Doorn]

Hi,

Some time ago I introduced LED classes to rt2x00.
For the USB drivers this has prooven to be tricky
since LED triggers are called in non-sleepable context
and USB drivers do need some sleep for register access.

As a workaround I introduced the in_atomic() check
which prints an error and skips the call. I am now
reading a discussion about in_atomic() on the netdev
mailinglist, and drivers are urged to remove the
usage as much as possible.

I must admit that I don't know if LED triggers work
in non-sleepable context by design or if it depends
on the calling trigger....

For rt2x00 there are now 2 options, either find the
trigger that is calling rt2x00 in non-sleepable context
and fix it or drop the LED class feature for USB drivers.

Has anybody recently tested the LED class option with
rt2500usb or rt73usb? And if so, do the following lines
appear in the log:
	Ignoring LED brightness command for led
If so, please post all those error messages so the problem
can be tracked down.

Otherwise I will start with either disabling LED handling
completely or create a large workaround which still uses
LED classes but works without LED triggers.
Depending on the amount of code, the LED triggers for PCI
drivers will also be sacrificed to keep the code as simple
as possible.

Ivo

Re: rt2x00: LED classes

[Ivo van Doorn]

Hi,

> I must admit that I don't know if LED triggers work
> in non-sleepable context by design or if it depends
> on the calling trigger....

On inspection of led_trigger_event() it seems to grab
a read_lock before calling the driver.
This means that USB drivers cannot use LED triggers.

I will see if I can simulate the behavior differently
where LED classes are still used but rt2x00 implements
its own version of LED triggers. Most likely this will result
in rt2x00 not be using the triggers provided by mac80211
for any of the drivers.

For the time being LED support for rt2500usb and rt73usb
will be disabled with CONFIG_BROKEN. A better solution will
hopefully be ready for 2.6.27.

Ivo