sparc32: Add more extensive documentation of sun4m interrupts.

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 53 insertions, 0 deletions

diff --git a/arch/sparc/kernel/sun4m_irq.c b/arch/sparc/kernel/sun4m_irq.c
index c6096fc70c61..ec66d4aab098 100644
--- a/arch/sparc/kernel/sun4m_irq.c
+++ b/arch/sparc/kernel/sun4m_irq.c
@@ -87,6 +87,59 @@ struct sun4m_irq_global __iomem *sun4m_irq_global;
 #define SUN4M_INT_SBUS(x)       (1 << (x+7))
 #define SUN4M_INT_VME(x)        (1 << (x))
 
+/* Interrupt level assignment on sun4m:
+ *
+ *      level           source
+ * ------------------------------------------------------------
+ *        1             softint-1
+ *        2             softint-2, VME/SBUS level 1
+ *        3             softint-3, VME/SBUS level 2
+ *        4             softint-4, onboard SCSI
+ *        5             softint-5, VME/SBUS level 3
+ *        6             softint-6, onboard ETHERNET
+ *        7             softint-7, VME/SBUS level 4
+ *        8             softint-8, onboard VIDEO
+ *        9             softint-9, VME/SBUS level 5, Module Interrupt
+ *       10             softint-10, system counter/timer
+ *       11             softint-11, VME/SBUS level 6, Floppy
+ *       12             softint-12, Keyboard/Mouse, Serial
+ *       13             softint-13, VME/SBUS level 7, ISDN Audio
+ *       14             softint-14, per-processor counter/timer
+ *       15             softint-15, Asynchronous Errors (broadcast)
+ *
+ * Each interrupt source is masked distinctly in the sun4m interrupt
+ * registers.  The PIL level alone is therefore ambiguous, since multiple
+ * interrupt sources map to a single PIL.
+ *
+ * This ambiguity is resolved in the 'intr' property for device nodes
+ * in the OF device tree.  Each 'intr' property entry is composed of
+ * two 32-bit words.  The first word is the IRQ priority value, which
+ * is what we're intersted in.  The second word is the IRQ vector, which
+ * is unused.
+ *
+ * The low 4 bits of the IRQ priority indicate the PIL, and the upper
+ * 4 bits indicate onboard vs. SBUS leveled vs. VME leveled.  0x20
+ * means onboard, 0x30 means SBUS leveled, and 0x40 means VME leveled.
+ *
+ * For example, an 'intr' IRQ priority value of 0x24 is onboard SCSI
+ * whereas a value of 0x33 is SBUS level 2.  Here are some sample
+ * 'intr' property IRQ priority values from ss4, ss5, ss10, ss20, and
+ * Tadpole S3 GX systems.
+ *
+ * esp:         0x24    onboard ESP SCSI
+ * le:          0x26    onboard Lance ETHERNET
+ * p9100:       0x32    SBUS level 1 P9100 video
+ * bpp:         0x33    SBUS level 2 BPP parallel port device
+ * DBRI:        0x39    SBUS level 5 DBRI ISDN audio
+ * SUNW,leo:    0x39    SBUS level 5 LEO video
+ * pcmcia:      0x3b    SBUS level 6 PCMCIA controller
+ * uctrl:       0x3b    SBUS level 6 UCTRL device
+ * modem:       0x3d    SBUS level 7 MODEM
+ * zs:          0x2c    onboard keyboard/mouse/serial
+ * floppy:      0x2b    onboard Floppy
+ * power:       0x22    onboard power device (XXX unknown mask bit XXX)
+ */
+
 /* These tables only apply for interrupts greater than 15..
  * 
  * any intr value below 0x10 is considered to be a soft-int