Messages in this thread | | | Date | Wed, 17 May 2006 09:23:42 -0700 | From | "Randy.Dunlap" <> | Subject | Re: [patch 15/50] genirq: doc: add design documentation |
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On Wed, 17 May 2006 02:16:23 +0200 Ingo Molnar wrote:
> From: Thomas Gleixner <tglx@linutronix.de> > > Add docbook file - includes API documentation.
Thanks. :)
> Index: linux-genirq.q/Documentation/DocBook/genericirq.tmpl > =================================================================== > --- /dev/null > +++ linux-genirq.q/Documentation/DocBook/genericirq.tmpl > @@ -0,0 +1,453 @@
> + <chapter id="rationale"> > + <title>Rationale</title> > + <para> > + The original implementation of interrupt handling in Linux is using > + the __do_IRQ() super-handler, which is able to deal with every > + type of interrupt logic. > + </para> > + <para> > + Originally, Russell King identified different types of handlers to > + build a quite universal set for the ARM interrupt handler > + implementation in Linux 2.5/2.6. He distiguished between: distinguished
> + <para> > + The original general IRQ implementation used hw_interrupt_type > + structures and their ->ack(), ->end() [etc.] callbcks to > + differentiate the flow control in the super-handler. This leads to > + a mix of flow logic and lowlevel hardware logic, and it also leads > + to unnecessary code duplication: for example in i386, there is a > + ioapic_level_irq and a ioapic_edge_irq irq-type which share many > + of the lowlevel details but have different flow handling. > + </para> > + <para> > + A more natural abstraction is the clean seperation of the separation (multiple locations) (or as my wife says, "there's 'a rat' in separate.")
> + 'irq flow' and the 'chip details'. > + </para> > + <para> > + Analysing a couple of architecture's IRQ subsystem implementations > + reveals that most of them can use a generic set of 'irq flow' > + methods and only need to add the chip level specific code. > + The seperation is also valuable for (sub)architectures > + which need specific quirks in the irq flow itself but not in the > + chip-details - and thus provides a more transparent IRQ subsystem > + design. > + </para> > + <para> > + Each interrupt descriptor has assigned its own highlevel flow s/has/is/
> + handler, which is normally one of the generic > + implementations. (This highlevel flow handler implementation also > + makes it simple to provide demultiplexing handlers which can be > + found in embedded platforms on various architectures.) > + </para> > + <para> > + The seperation makes the generic interrupt handling layer more > + flexible and extensible. For example, an (sub)architecture can > + use a generic irq-flow implementation for 'level type' interrupts > + and add a (sub)architecture specific 'edge type' implementation. > + </para> > + <para> > + To make the transition to the new model easier and prevent the > + breakage of existing implementations the __do_IRQ() super-handler add comma after "implementations"
> + is still available. This leads to a kind of duality for the time > + being. Over time the new model should be used in more and more > + architectures, as it enables smaller and cleaner IRQ subsystems. > + </para> > + </chapter> > + <chapter id="bugs"> > + <title>Known Bugs And Assumptions</title> > + <para> > + None (knock on wood). > + </para> > + </chapter> > +
> + <sect2> > + <title>Default flow implementations</title> > + <sect3> > + <title>Helper functions</title> > + <para> > + The helper functions call the chip primitives and > + are used by the default flow implementations. > + Following helper functions are implemented (simplified excerpt): The following ... (multiple locations)
> + <sect3> > + <title>Default Edge IRQ flow handler</title> > + <para> > + handle_edge_irq provides a generic implementation > + for edge interrupts. edge-triggered interrupts. (IMO)
> + <chapter id="doirq"> > + <title>__do_IRQ entry point</title> > + <para> > + The original implementation __do_IRQ() is an alternative entry > + point for all types of interrupts. > + </para> > + <para> > + This handler turned out to be not suitable for all > + interrupt hardware and was therefor reimplemented with split therefore
> + functionality for egde/level/simple/percpu interrupts. This is not > + only a functional optimization. It also shortenes code pathes for shortens code paths
> + interrupts.
HTH. --- ~Randy - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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