[alsa-devel] Echoaudio, suspend/resume question on rawmidi device

Giuliano Pochini pochini at shiny.it
Sun Jan 3 21:55:45 CET 2010

I have some patches that add PM support to all echoaudio drivers. It seems
to work fine, but it has been tested on two cards only and the rawmidi
device hasn't been tested at all. I can't test it because
suspend-to-anything does not work on my pmac. I want to be sure at least it
cannot deadlock.

 * On suspend:

Rawmidi input is interrupt-driven. The driver tells the card to stop
accepting data.

Rawmidi output is timer-driven. The driver uses a timer to check if the
card's output buffer has room for more data to send. Do del_timer_sync()
and wait until all buffered data is sent, which may take 20ms (64 bytes at

 * On resume:

Input: Re-enable midi in.

Output: Restart the timer.

Do you see any race condition or weak points in this scheme, especially in
the midi-out part ? Is del_timer_sync() safe ?


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