On 09/03/2016 05:17 PM, Alan Stern wrote:
On Sat, 3 Sep 2016, Jacek Anaszewski wrote:
Maybe it would make more sense, in this case, to allow only three
possibilities for a USB port activity trigger. Toggle the LED
whenever:
There is activity on the specified port, or
There is any activity on any port on the specified hub, or
There is any USB activity on any port.
That ought to cover most of the normal use cases, and it would be
simple enough to implement.
What would be the benefit of having a USB port activity trigger,
for which we would be specifying the port to observe, but in the same
time we would react on any activity on any port (cases 1 and 3)?
I meant these three cases to be mutually exclusive. For a given LED,
you could have only one of those trigger types (like mentioned above,
only one trigger per LED). For example, you might accept any one of:
echo usb1-4.2 >/sys/class/led/foo/trigger
echo hub1-4 >/sys/class/led/foo/trigger
echo usb >/sys/class/led/foo/trigger
Yes, it would be possible to have a port-specific trigger for one LED
and an overall USB activity trigger for another LED. I don't know how
useful this would be -- you could probably imagine some unlikely
scenario.
The point is that doing things this way wouldn't require any API
violations, and it would allow users to do almost all of the things
they are likely to want.
We'd have to define single API for generating USB trigger event,
so as not enforce addition of three different API calls to the USB
drivers.
Of course this trigger represents yet another type of triggers, that
don't require exposing an API for generating events, but instead
register as listeners to some notifiers. I missed that initially.
The USB core would need only one LED-API call, which it would make upon
the completion of an URB. The trigger code should be able to handle
all the rest (i.e., see which LEDs should be triggered by that URB).
This is assured by the LED trigger core.
The type of USB events that the LED should react upon could be
defined by parsing the value written to the sysfs file.
There is only one type of event: completion of an URB. Triggers would
differ depending only on the device/port that the URB was aimed at.
_That_ information could be defined by parsing the value written to the
sysfs file.
This of course implies, that we should have single LED USB port trigger.
The remaining issue is the sysfs interface design for defining and
presenting multiple USB ports. I'm still in favour of a single
attribute with space separated list. This scheme is commonly used
in existing interfaces.
No such interface is needed if you do things the way I outlined above.
Each trigger would require the user to specify either one port, one
hub, or nothing at all. Multiple ports would not be used.
The patch assumes that it is possible to register trigger for many
ports.
--
Best regards,
Jacek Anaszewski
--
To unsubscribe from this list: send the line "unsubscribe linux-doc" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
