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. -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
