Messages in this thread | | | Date | Wed, 12 Sep 2012 03:32:05 -0700 | From | Anton Vorontsov <> | Subject | Re: [RFC] tty/serial/kgdboc: Add and wire up clear_irqs callback |
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On Wed, Sep 12, 2012 at 10:44:20AM +0100, Alan Cox wrote: > > Of course, if Alan is OK with this, I'm more than OK too. :-) > > It may well be better. > > > (But the polling routines would need to clear all interrupts, not > > just rx/tx. For example, if the controller indicated some error, and > > nobody clears it, then we'll start reentering infinitely.) > > For a lot of devices and platforms you'd probably mask them instead ?
If there is no way to clear them, yes, we obviously would want to mask them before using the port for NMI debugger. Then we'd need three callbacks:
- mask_all_irqs_but_rx() -- used before we want to start using the port for the NMI debugger; - clear_rx_irq() -- (optional) clears rx IRQ for controllers that need it; - restore_irqs() -- unmasks interrupts that were previously masked.
If we ever encounter a case when just clearing interrupts doesn't work, we can surely implement the above scheme... It's just so far I don't see any need to over-design this, but again, it's your call, I told my opinion on this, but I'll do whatever you guys like more. :-)
> > > If you use a clear_irqs callback, you can drop characters if > > > one arrives between the last character buffer read and calling > > > clear_irqs. > > > > Only if we call clear_irqs() after reading the characters, but we do > > it before. So if new characters are available, we will reenter NMI, > > which is OK. > > Recursively or not... again you get platform specific magic in places > we don't want.
I really really don't see how this is platform-specific. All we ask the serial driver is to quiesce its interrupt. Whether we can handle NMIs/IRQs recursively or not is not serial driver's worry, since its IRQ handler is not going to fire anyway. The polling routines already gave us the power to steal/inject the data, so now we're stealing the interrupt too.
How we use the callback is indeed platform-specific, but so is the whole KGDB, and that knowledge is hidden there.
For serial driver it's all pretty much clear: lower the interrupt, but don't turn off rx detection.
Thanks!
Anton.
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