Linux-2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 173 insertions, 0 deletions

diff --git a/Documentation/arm/Interrupts b/Documentation/arm/Interrupts
new file mode 100644
index 000000000000..72c93de8cd4e
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+2.5.2-rmk5
+----------
+
+This is the first kernel that contains a major shake up of some of the
+major architecture-specific subsystems.
+
+Firstly, it contains some pretty major changes to the way we handle the
+MMU TLB.  Each MMU TLB variant is now handled completely separately -
+we have TLB v3, TLB v4 (without write buffer), TLB v4 (with write buffer),
+and finally TLB v4 (with write buffer, with I TLB invalidate entry).
+There is more assembly code inside each of these functions, mainly to
+allow more flexible TLB handling for the future.
+
+Secondly, the IRQ subsystem.
+
+The 2.5 kernels will be having major changes to the way IRQs are handled.
+Unfortunately, this means that machine types that touch the irq_desc[]
+array (basically all machine types) will break, and this means every
+machine type that we currently have.
+
+Lets take an example.  On the Assabet with Neponset, we have:
+
+                  GPIO25                 IRR:2
+        SA1100 ------------> Neponset -----------> SA1111
+                                         IIR:1
+                                      -----------> USAR
+                                         IIR:0
+                                      -----------> SMC9196
+
+The way stuff currently works, all SA1111 interrupts are mutually
+exclusive of each other - if you're processing one interrupt from the
+SA1111 and another comes in, you have to wait for that interrupt to
+finish processing before you can service the new interrupt.  Eg, an
+IDE PIO-based interrupt on the SA1111 excludes all other SA1111 and
+SMC9196 interrupts until it has finished transferring its multi-sector
+data, which can be a long time.  Note also that since we loop in the
+SA1111 IRQ handler, SA1111 IRQs can hold off SMC9196 IRQs indefinitely.
+
+
+The new approach brings several new ideas...
+
+We introduce the concept of a "parent" and a "child".  For example,
+to the Neponset handler, the "parent" is GPIO25, and the "children"d
+are SA1111, SMC9196 and USAR.
+
+We also bring the idea of an IRQ "chip" (mainly to reduce the size of
+the irqdesc array).  This doesn't have to be a real "IC"; indeed the
+SA11x0 IRQs are handled by two separate "chip" structures, one for
+GPIO0-10, and another for all the rest.  It is just a container for
+the various operations (maybe this'll change to a better name).
+This structure has the following operations:
+
+struct irqchip {
+        /*
+         * Acknowledge the IRQ.
+         * If this is a level-based IRQ, then it is expected to mask the IRQ
+         * as well.
+         */
+        void (*ack)(unsigned int irq);
+        /*
+         * Mask the IRQ in hardware.
+         */
+        void (*mask)(unsigned int irq);
+        /*
+         * Unmask the IRQ in hardware.
+         */
+        void (*unmask)(unsigned int irq);
+        /*
+         * Re-run the IRQ
+         */
+        void (*rerun)(unsigned int irq);
+        /*
+         * Set the type of the IRQ.
+         */
+        int (*type)(unsigned int irq, unsigned int, type);
+};
+
+ack    - required.  May be the same function as mask for IRQs
+         handled by do_level_IRQ.
+mask   - required.
+unmask - required.
+rerun  - optional.  Not required if you're using do_level_IRQ for all
+         IRQs that use this 'irqchip'.  Generally expected to re-trigger
+         the hardware IRQ if possible.  If not, may call the handler
+	 directly.
+type   - optional.  If you don't support changing the type of an IRQ,
+         it should be null so people can detect if they are unable to
+         set the IRQ type.
+
+For each IRQ, we keep the following information:
+
+        - "disable" depth (number of disable_irq()s without enable_irq()s)
+        - flags indicating what we can do with this IRQ (valid, probe,
+          noautounmask) as before
+        - status of the IRQ (probing, enable, etc)
+        - chip
+        - per-IRQ handler
+        - irqaction structure list
+
+The handler can be one of the 3 standard handlers - "level", "edge" and
+"simple", or your own specific handler if you need to do something special.
+
+The "level" handler is what we currently have - its pretty simple.
+"edge" knows about the brokenness of such IRQ implementations - that you
+need to leave the hardware IRQ enabled while processing it, and queueing
+further IRQ events should the IRQ happen again while processing.  The
+"simple" handler is very basic, and does not perform any hardware
+manipulation, nor state tracking.  This is useful for things like the
+SMC9196 and USAR above.
+
+So, what's changed?
+
+1. Machine implementations must not write to the irqdesc array.
+
+2. New functions to manipulate the irqdesc array.  The first 4 are expected
+   to be useful only to machine specific code.  The last is recommended to
+   only be used by machine specific code, but may be used in drivers if
+   absolutely necessary.
+
+        set_irq_chip(irq,chip)
+
+                Set the mask/unmask methods for handling this IRQ
+
+        set_irq_handler(irq,handler)
+
+                Set the handler for this IRQ (level, edge, simple)
+
+        set_irq_chained_handler(irq,handler)
+
+                Set a "chained" handler for this IRQ - automatically
+                enables this IRQ (eg, Neponset and SA1111 handlers).
+
+        set_irq_flags(irq,flags)
+
+                Set the valid/probe/noautoenable flags.
+
+        set_irq_type(irq,type)
+
+                Set active the IRQ edge(s)/level.  This replaces the
+                SA1111 INTPOL manipulation, and the set_GPIO_IRQ_edge()
+                function.  Type should be one of the following:
+
+                #define IRQT_NOEDGE     (0)
+                #define IRQT_RISING     (__IRQT_RISEDGE)
+                #define IRQT_FALLING    (__IRQT_FALEDGE)
+                #define IRQT_BOTHEDGE   (__IRQT_RISEDGE|__IRQT_FALEDGE)
+                #define IRQT_LOW        (__IRQT_LOWLVL)
+                #define IRQT_HIGH       (__IRQT_HIGHLVL)
+
+3. set_GPIO_IRQ_edge() is obsolete, and should be replaced by set_irq_type.
+
+4. Direct access to SA1111 INTPOL is depreciated.  Use set_irq_type instead.
+
+5. A handler is expected to perform any necessary acknowledgement of the
+   parent IRQ via the correct chip specific function.  For instance, if
+   the SA1111 is directly connected to a SA1110 GPIO, then you should
+   acknowledge the SA1110 IRQ each time you re-read the SA1111 IRQ status.
+
+6. For any child which doesn't have its own IRQ enable/disable controls
+   (eg, SMC9196), the handler must mask or acknowledge the parent IRQ
+   while the child handler is called, and the child handler should be the
+   "simple" handler (not "edge" nor "level").  After the handler completes,
+   the parent IRQ should be unmasked, and the status of all children must
+   be re-checked for pending events.  (see the Neponset IRQ handler for
+   details).
+
+7. fixup_irq() is gone, as is include/asm-arm/arch-*/irq.h
+
+Please note that this will not solve all problems - some of them are
+hardware based.  Mixing level-based and edge-based IRQs on the same
+parent signal (eg neponset) is one such area where a software based
+solution can't provide the full answer to low IRQ latency.
+