m68k/mac: fix nubus slot irq disable and shutdown

Improve NuBus slot interrupt handling code and documentation. This patch fixes the NuBus NIC (mac8390) in my Quadra 700.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

2 files changed, 108 insertions, 42 deletions

diff --git a/arch/m68k/mac/macints.c b/arch/m68k/mac/macints.c
index 41dd164aac27..74f5a97c9860 100644
--- a/arch/m68k/mac/macints.c
+++ b/arch/m68k/mac/macints.c
@@ -151,10 +151,15 @@ irqreturn_t mac_debug_handler(int, void *);
 
 /* #define DEBUG_MACINTS */
 
+static unsigned int mac_irq_startup(struct irq_data *);
+static void mac_irq_shutdown(struct irq_data *);
+
 static struct irq_chip mac_irq_chip = {
         .name           = "mac",
         .irq_enable     = mac_irq_enable,
         .irq_disable    = mac_irq_disable,
+        .irq_startup    = mac_irq_startup,
+        .irq_shutdown   = mac_irq_shutdown,
 };
 
 void __init mac_init_IRQ(void)
@@ -274,6 +279,28 @@ void mac_irq_disable(struct irq_data *data)
         }
 }
 
+static unsigned int mac_irq_startup(struct irq_data *data)
+{
+        int irq = data->irq;
+
+        if (IRQ_SRC(irq) == 7 && !oss_present)
+                via_nubus_irq_startup(irq);
+        else
+                mac_irq_enable(data);
+
+        return 0;
+}
+
+static void mac_irq_shutdown(struct irq_data *data)
+{
+        int irq = data->irq;
+
+        if (IRQ_SRC(irq) == 7 && !oss_present)
+                via_nubus_irq_shutdown(irq);
+        else
+                mac_irq_disable(data);
+}
+
 static int num_debug[8];
 
 irqreturn_t mac_debug_handler(int irq, void *dev_id)
diff --git a/arch/m68k/mac/via.c b/arch/m68k/mac/via.c
index 642b44615f78..97996a48b048 100644
--- a/arch/m68k/mac/via.c
+++ b/arch/m68k/mac/via.c
@@ -63,18 +63,47 @@ static int gIER,gIFR,gBufA,gBufB;
 #define MAC_CLOCK_LOW           (MAC_CLOCK_TICK&0xFF)
 #define MAC_CLOCK_HIGH          (MAC_CLOCK_TICK>>8)
 
-/* To disable a NuBus slot on Quadras we make that slot IRQ line an output set
- * high. On RBV we just use the slot interrupt enable register. On Macs with
- * genuine VIA chips we must use nubus_disabled to keep track of disabled slot
- * interrupts. When any slot IRQ is disabled we mask the (edge triggered) CA1
- * or "SLOTS" interrupt. When no slot is disabled, we unmask the CA1 interrupt.
- * So, on genuine VIAs, having more than one NuBus IRQ can mean trouble,
- * because closing one of those drivers can mask all of the NuBus interrupts.
- * Also, since we can't mask the unregistered slot IRQs on genuine VIAs, it's
- * possible to get interrupts from cards that MacOS or the ROM has configured
- * but we have not. FWIW, "Designing Cards and Drivers for Macintosh II and
- * Macintosh SE", page 9-8, says, a slot IRQ with no driver would crash MacOS.
+
+/*
+ * On Macs with a genuine VIA chip there is no way to mask an individual slot
+ * interrupt. This limitation also seems to apply to VIA clone logic cores in
+ * Quadra-like ASICs. (RBV and OSS machines don't have this limitation.)
+ *
+ * We used to fake it by configuring the relevent VIA pin as an output
+ * (to mask the interrupt) or input (to unmask). That scheme did not work on
+ * (at least) the Quadra 700. A NuBus card's /NMRQ signal is an open-collector
+ * circuit (see Designing Cards and Drivers for Macintosh II and Macintosh SE,
+ * p. 10-11 etc) but VIA outputs are not (see datasheet).
+ *
+ * Driving these outputs high must cause the VIA to source current and the
+ * card to sink current when it asserts /NMRQ. Current will flow but the pin
+ * voltage is uncertain and so the /NMRQ condition may still cause a transition
+ * at the VIA2 CA1 input (which explains the lost interrupts). A side effect
+ * is that a disabled slot IRQ can never be tested as pending or not.
+ *
+ * Driving these outputs low doesn't work either. All the slot /NMRQ lines are
+ * (active low) OR'd together to generate the CA1 (aka "SLOTS") interrupt (see
+ * The Guide To Macintosh Family Hardware, 2nd edition p. 167). If we drive a
+ * disabled /NMRQ line low, the falling edge immediately triggers a CA1
+ * interrupt and all slot interrupts after that will generate no transition
+ * and therefore no interrupt, even after being re-enabled.
+ *
+ * So we make the VIA port A I/O lines inputs and use nubus_disabled to keep
+ * track of their states. When any slot IRQ becomes disabled we mask the CA1
+ * umbrella interrupt. Only when all slot IRQs become enabled do we unmask
+ * the CA1 interrupt. It must remain enabled even when cards have no interrupt
+ * handler registered. Drivers must therefore disable a slot interrupt at the
+ * device before they call free_irq (like shared and autovector interrupts).
+ *
+ * There is also a related problem when MacOS is used to boot Linux. A network
+ * card brought up by a MacOS driver may raise an interrupt while Linux boots.
+ * This can be fatal since it can't be handled until the right driver loads
+ * (if such a driver exists at all). Apparently related to this hardware
+ * limitation, "Designing Cards and Drivers", p. 9-8, says that a slot
+ * interrupt with no driver would crash MacOS (the book was written before
+ * the appearance of Macs with RBV or OSS).
  */
+
 static u8 nubus_disabled;
 
 void via_debug_dump(void);
@@ -354,34 +383,55 @@ void __init via_nubus_init(void)
                 via2[gBufB] |= 0x02;
         }
 
-        /* Disable all the slot interrupts (where possible). */
+        /*
+         * Disable the slot interrupts. On some hardware that's not possible.
+         * On some hardware it's unclear what all of these I/O lines do.
+         */
 
         switch (macintosh_config->via_type) {
         case MAC_VIA_II:
-                /* Just make the port A lines inputs. */
-                switch(macintosh_config->ident) {
-                case MAC_MODEL_II:
-                case MAC_MODEL_IIX:
-                case MAC_MODEL_IICX:
-                case MAC_MODEL_SE30:
-                        /* The top two bits are RAM size outputs. */
-                        via2[vDirA] &= 0xC0;
-                        break;
-                default:
-                        via2[vDirA] &= 0x80;
-                }
+        case MAC_VIA_QUADRA:
+                pr_debug("VIA2 vDirA is 0x%02X\n", via2[vDirA]);
                 break;
         case MAC_VIA_IIci:
                 /* RBV. Disable all the slot interrupts. SIER works like IER. */
                 via2[rSIER] = 0x7F;
                 break;
+        }
+}
+
+void via_nubus_irq_startup(int irq)
+{
+        int irq_idx = IRQ_IDX(irq);
+
+        switch (macintosh_config->via_type) {
+        case MAC_VIA_II:
         case MAC_VIA_QUADRA:
-                /* Disable the inactive slot interrupts by making those lines outputs. */
-                if ((macintosh_config->adb_type != MAC_ADB_PB1) &&
-                    (macintosh_config->adb_type != MAC_ADB_PB2)) {
-                        via2[vBufA] |= 0x7F;
-                        via2[vDirA] |= 0x7F;
+                /* Make the port A line an input. Probably redundant. */
+                if (macintosh_config->via_type == MAC_VIA_II) {
+                        /* The top two bits are RAM size outputs. */
+                        via2[vDirA] &= 0xC0 | ~(1 << irq_idx);
+                } else {
+                        /* Allow NuBus slots 9 through F. */
+                        via2[vDirA] &= 0x80 | ~(1 << irq_idx);
                 }
+                /* fall through */
+        case MAC_VIA_IIci:
+                via_irq_enable(irq);
+                break;
+        }
+}
+
+void via_nubus_irq_shutdown(int irq)
+{
+        switch (macintosh_config->via_type) {
+        case MAC_VIA_II:
+        case MAC_VIA_QUADRA:
+                /* Ensure that the umbrella CA1 interrupt remains enabled. */
+                via_irq_enable(irq);
+                break;
+        case MAC_VIA_IIci:
+                via_irq_disable(irq);
                 break;
         }
 }
@@ -507,6 +557,7 @@ void via_irq_enable(int irq) {
         } else if (irq_src == 7) {
                 switch (macintosh_config->via_type) {
                 case MAC_VIA_II:
+                case MAC_VIA_QUADRA:
                         nubus_disabled &= ~(1 << irq_idx);
                         /* Enable the CA1 interrupt when no slot is disabled. */
                         if (!nubus_disabled)
@@ -518,14 +569,6 @@ void via_irq_enable(int irq) {
                          */
                         via2[rSIER] = IER_SET_BIT(irq_idx);
                         break;
-                case MAC_VIA_QUADRA:
-                        /* Make the port A line an input to enable the slot irq.
-                         * But not on PowerBooks, that's ADB.
-                         */
-                        if ((macintosh_config->adb_type != MAC_ADB_PB1) &&
-                            (macintosh_config->adb_type != MAC_ADB_PB2))
-                                via2[vDirA] &= ~(1 << irq_idx);
-                        break;
                 }
         }
 }
@@ -545,6 +588,7 @@ void via_irq_disable(int irq) {
         } else if (irq_src == 7) {
                 switch (macintosh_config->via_type) {
                 case MAC_VIA_II:
+                case MAC_VIA_QUADRA:
                         nubus_disabled |= 1 << irq_idx;
                         if (nubus_disabled)
                                 via2[gIER] = IER_CLR_BIT(1);
@@ -552,11 +596,6 @@ void via_irq_disable(int irq) {
                 case MAC_VIA_IIci:
                         via2[rSIER] = IER_CLR_BIT(irq_idx);
                         break;
-                case MAC_VIA_QUADRA:
-                        if ((macintosh_config->adb_type != MAC_ADB_PB1) &&
-                            (macintosh_config->adb_type != MAC_ADB_PB2))
-                                via2[vDirA] |= 1 << irq_idx;
-                        break;
                 }
         }
 }