read_irq
chan_interrupt(line, line->read_irq);
um_free_irq(chan->line->read_irq, chan);
um_free_irq(chan->line->read_irq, chan);
deactivate_chan(line->chan_in, line->read_irq);
chan_interrupt(line, line->read_irq);
line->read_irq = err;
int read_irq, write_irq;
read_irq(spa, &dsisr, &dar, &pe_handle);