MIPS: DECstation I/O ASIC DMA interrupt classes

This change complements commits d0da7c002f7b2a93582187a9e3f73891a01d8ee4
[MIPS: DEC: Convert to new irq_chip functions] and
5359b938c088423a28c41499f183cd10824c1816 [MIPS: DECstation I/O ASIC DMA
interrupt handling fix] and implements automatic handling of the two
classes of DMA interrupts the I/O ASIC implements, informational and
errors.

Informational DMA interrupts do not stop the transfer and use the
`handle_edge_irq' handler that clears the request right away so that
another request may be recorded while the previous is being handled.

DMA error interrupts stop the transfer and require a corrective action
before DMA can be reenabled. Therefore they use the `handle_fasteoi_irq'
handler that only clears the request on the way out. Because MIPS
processor interrupt inputs, one of which the I/O ASIC's interrupt
controller is cascaded to, are level-triggered it is recommended that
error DMA interrupt action handlers are registered with the IRQF_ONESHOT
flag set so that they are run with the interrupt line masked.

This change removes the export of clear_ioasic_dma_irq that now does not
have to be called by device drivers to clear interrupts explicitly
anymore. Originally these interrupts were cleared in the .end handler of
the `irq_chip' structure, before it was removed.

Signed-off-by: Maciej W. Rozycki <[e-mail]>
Cc: [e-mail]
Patchwork: https://patchwork.linux-mips.org/patch/5874/
Signed-off-by: Ralf Baechle <[e-mail]>

arch/mips/dec/ioasic-irq.c

···
 /*
  *	DEC I/O ASIC interrupts.
  *
- *	Copyright (c) 2002, 2003  Maciej W. Rozycki
+ *	Copyright (c) 2002, 2003, 2013  Maciej W. Rozycki
  *
  *	This program is free software; you can redistribute it and/or
  *	modify it under the terms of the GNU General Public License
···
 	.irq_unmask = unmask_ioasic_irq,
 };
 
-void clear_ioasic_dma_irq(unsigned int irq)
+static void clear_ioasic_dma_irq(struct irq_data *d)
 {
 	u32 sir;
 
-	sir = ~(1 << (irq - ioasic_irq_base));
+	sir = ~(1 << (d->irq - ioasic_irq_base));
 	ioasic_write(IO_REG_SIR, sir);
+	fast_iob();
 }
 
 static struct irq_chip ioasic_dma_irq_type = {
 	.name = "IO-ASIC-DMA",
-	.irq_ack = ack_ioasic_irq,
+	.irq_ack = clear_ioasic_dma_irq,
 	.irq_mask = mask_ioasic_irq,
-	.irq_mask_ack = ack_ioasic_irq,
 	.irq_unmask = unmask_ioasic_irq,
+	.irq_eoi = clear_ioasic_dma_irq,
 };
+
+/*
+ * I/O ASIC implements two kinds of DMA interrupts, informational and
+ * error interrupts.
+ *
+ * The formers do not stop DMA and should be cleared as soon as possible
+ * so that if they retrigger before the handler has completed, usually as
+ * a side effect of actions taken by the handler, then they are reissued.
+ * These use the `handle_edge_irq' handler that clears the request right
+ * away.
+ *
+ * The latters stop DMA and do not resume it until the interrupt has been
+ * cleared.  This cannot be done until after a corrective action has been
+ * taken and this also means they will not retrigger.  Therefore they use
+ * the `handle_fasteoi_irq' handler that only clears the request on the
+ * way out.  Because MIPS processor interrupt inputs, one of which the I/O
+ * ASIC is cascaded to, are level-triggered it is recommended that error
+ * DMA interrupt action handlers are registered with the IRQF_ONESHOT flag
+ * set so that they are run with the interrupt line masked.
+ *
+ * This mask has `1' bits in the positions of informational interrupts.
+ */
+#define IO_IRQ_DMA_INFO							\
+	(IO_IRQ_MASK(IO_INR_SCC0A_RXDMA) |				\
+	 IO_IRQ_MASK(IO_INR_SCC1A_RXDMA) |				\
+	 IO_IRQ_MASK(IO_INR_ISDN_TXDMA) |				\
+	 IO_IRQ_MASK(IO_INR_ISDN_RXDMA) |				\
+	 IO_IRQ_MASK(IO_INR_ASC_DMA))
 
 void __init init_ioasic_irqs(int base)
 {
···
 		irq_set_chip_and_handler(i, &ioasic_irq_type,
 					 handle_level_irq);
 	for (; i < base + IO_IRQ_LINES; i++)
-		irq_set_chip(i, &ioasic_dma_irq_type);
+		irq_set_chip_and_handler(i, &ioasic_dma_irq_type,
+					 1 << (i - base) & IO_IRQ_DMA_INFO ?
+					 handle_edge_irq : handle_fasteoi_irq);
 
 	ioasic_irq_base = base;
 }

arch/mips/include/asm/dec/ioasic.h

···
 	return ioasic_base[reg / 4];
 }
 
-extern void clear_ioasic_dma_irq(unsigned int irq);
-
 extern void init_ioasic_irqs(int base);
 
 extern int dec_ioasic_clocksource_init(void);

drivers/net/ethernet/amd/declance.c

···
 {
 	struct net_device *dev = dev_id;
 
-	clear_ioasic_dma_irq(irq);
 	printk(KERN_ERR "%s: DMA error\n", dev->name);
 	return IRQ_HANDLED;
 }
···
 	if (lp->dma_irq >= 0) {
 		unsigned long flags;
 
-		if (request_irq(lp->dma_irq, lance_dma_merr_int, 0,
+		if (request_irq(lp->dma_irq, lance_dma_merr_int, IRQF_ONESHOT,
 				"lance error", dev)) {
 			free_irq(dev->irq, dev);
 			printk("%s: Can't get DMA IRQ %d\n", dev->name,