On Wed, 17 Feb 2021, Song Bao Hua (Barry Song) wrote: > > On Sat, 13 Feb 2021, Song Bao Hua (Barry Song) wrote: > > > > > > > > So what is really confusing and a pain to me is that: For years > > > people like me have been writing device drivers with the idea that > > > irq handlers run with interrupts disabled after those commits in > > > genirq. So I don't need to care about if some other IRQs on the same > > > cpu will jump out to access the data the current IRQ handler is > > > accessing. > > > > > > but it turns out the assumption is not true on some platform. So > > > should I start to program devices driver with the new idea > > > interrupts can actually come while irqhandler is running? > > > > > > That's the question which really bothers me. > > > > > > > That scenario seems a little contrived to me (drivers for two or more > > devices sharing state through their interrupt handlers). Is it real? I > > suppose every platform has its quirks. The irq lock in > > sonic_interrupt() is only there because of a platform quirk (the same > > device can trigger either of two IRQs). Anyway, no-one expects all > > drivers to work on all platforms; I don't know why it bothers you so > > much when platforms differ. > > Basically, we wrote drivers with the assumption that this driver will be > cross-platform. (Of course there are some drivers which can only work on > one platform, for example, if the IP of the device is only used in one > platform as an internal component of a specific SoC.) > > So once a device has two or more interrupts, we need to consider one > interrupt might preempt another one on m68k on the same cpu if we also > want to support this driver on m68k. this usually doesn't matter on > other platforms. >
When users show up who desire to run your drivers on their platform, you can expect them to bring patches and a MAINTAINERS file entry. AFAIK, Linux development has always worked that way. Besides, not all m68k platforms implement priority masking. So there's no problem with portability to m68k per se. > on the other hand, there are more than 400 irqs_disabled() in kernel, I > am really not sure if they are running with the knowledge that the true > irqs_disabled() actually means some interrupts are off and some others > are still open on m68k. Firstly, use of irqs_disabled() is considered an antipattern by some developers. Please see, https://lore.kernel.org/linux-scsi/X8pfD5XtLoOygdez@lx-t490/ and commit e6b6be53ec91 ("Merge branch 'net-in_interrupt-cleanup-and-fixes'") This means that the differences in semantics between the irqs_disabled() implementations on various architectures are moot. Secondly, the existence of irqs_disabled() call sites does not imply a flaw in your drivers nor in the m68k interrupt scheme. The actual semantic differences are immaterial at many (all?) of these call sites. > Or they are running with the assumption that the true irqs_disabled() > means IRQ is totally quiet? If the latter is true, those drivers might > fail to work on m68k as well. > Yes it's possible, and that was my fear too back in 2017 when I raised the same question with the m68k maintainer. But I never found any code making that assumption. If you know of such a bug, do tell. So far, your fears remain unfounded. > Thanks > Barry >
