On Tue, Jun 24, 2008 at 04:00:16AM +0400, Anton Vorontsov wrote: > On Tue, Jun 24, 2008 at 01:51:41AM +0200, Ingo Molnar wrote: > > > > * Anton Vorontsov <avorontsov@xxxxxxxxxxxxx> wrote: > > > > > IDE interrupt handler relies on the fact that, if necessary, hardirqs > > > will re-trigger on ISR exit. With fully preemtable IRQs this seems to > > > be not true, since if hardirq thread is currently running, and the > > > same IRQ raised again, then this IRQ will be simply lost. > > > > actually no, that should not happen - if -rt loses an IRQ then something > > broke in the threaded IRQ code. It's supposed to be a drop-in, > > compatible IRQ flow with no driver changes needed. > > ..just as I thought, the bug somewhere deeper... heh. Ok, a bit more investigation showed that this is indeed not RT specific per see, but issue emerges only on RT-style IRQ handlers + alim15x3 IDE controller (for example, PDC20269 works ok). The difference is that that with RT: low-level (non-threaded) IRQ handler masks IDE IRQ, then wakes up appropriate IRQ thread, which calls IDE handler, and then, after IDE handler exits, thread routine unmasks IDE IRQ. Without RT: low-level non-threaded IRQ handler does not mask specific IRQ, but disables local interrupts, and calls IDE handler directly. The bug, as I see it, in the alim15x3 (ULi M5228) hardware: for some reason it does not hold IRQ line, but rises it for some short period of time (while the drive itself rises and holds it correctly -- I'm seeing it via oscilloscope). So this scheme does not work: mask_irq() ...do something that will trigger IDE interrupt... unmask_irq() Because at the unmask_irq() time IDE IRQ is gone already, and interrupt controller could not notice it (interrupts are level sensitive). I did following test: disable RT + insert mask/unmask sequence in the IDE IRQ handler, and I got the same behaviour as with RT enabled. Also, further testing showed that this issue isn't drive-specific, i.e. with a delay inserted before the unmask_irq(), the bug shows with any drive I have. So, in summary: I think that the patch is still correct as a hw bug workaround (I'll need to correct its comments and description though). -- Anton Vorontsov email: cbouatmailru@xxxxxxxxx irc://irc.freenode.net/bd2 -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
