[PATCH] MIPS: DECstation I/O ASIC DMA interrupt handling fix

["Maciej W. Rozycki" <macro@xxxxxxxxxxxxxx>]

This change complements commit d0da7c002f7b2a93582187a9e3f73891a01d8ee4 
and brings clear_ioasic_irq back, renaming it to clear_ioasic_dma_irq at 
the same time, to make I/O ASIC DMA interrupts functional.

Unlike ordinary I/O ASIC interrupts DMA interrupts need to be deasserted 
by software by writing 0 to the respective bit in I/O ASIC's System 
Interrupt Register (SIR), similarly to how CP0.Cause.IP0 and CP0.Cause.IP1 
bits are handled in the CPU (the difference is SIR DMA interrupt bits are 
R/W0C so there's no need for an RMW cycle).  Otherwise the handler is 
reentered over and over again.

The only current user is the DEC LANCE Ethernet driver and its extremely 
uncommon DMA memory error handler that does not care when exactly the 
interrupt is cleared.  Anticipating the use of DMA interrupts by the Zilog 
SCC driver this change however exports clear_ioasic_dma_irq for device 
drivers to choose the right application-specific sequence to clear the 
request explicitly rather than calling it implicitly in the .irq_eoi 
handler of `struct irq_chip'.  Previously these interrupts were cleared in 
the .end handler of the said structure, before it was removed.

Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxxxxxxxx>
---
linux-dec-ioasic-dma-irq.patch
Index: linux/arch/mips/dec/ioasic-irq.c
===================================================================
--- linux.orig/arch/mips/dec/ioasic-irq.c
+++ linux/arch/mips/dec/ioasic-irq.c
@@ -51,6 +51,14 @@ static struct irq_chip ioasic_irq_type =
 	.irq_unmask = unmask_ioasic_irq,
 };
 
+void clear_ioasic_dma_irq(unsigned int irq)
+{
+	u32 sir;
+
+	sir = ~(1 << (irq - ioasic_irq_base));
+	ioasic_write(IO_REG_SIR, sir);
+}
+
 static struct irq_chip ioasic_dma_irq_type = {
 	.name = "IO-ASIC-DMA",
 	.irq_ack = ack_ioasic_irq,
Index: linux/arch/mips/include/asm/dec/ioasic.h
===================================================================
--- linux.orig/arch/mips/include/asm/dec/ioasic.h
+++ linux/arch/mips/include/asm/dec/ioasic.h
@@ -31,6 +31,8 @@ static inline u32 ioasic_read(unsigned i
 	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);
Index: linux/drivers/net/ethernet/amd/declance.c
===================================================================
--- linux.orig/drivers/net/ethernet/amd/declance.c
+++ linux/drivers/net/ethernet/amd/declance.c
@@ -725,6 +725,7 @@ static irqreturn_t lance_dma_merr_int(in
 {
 	struct net_device *dev = dev_id;
 
+	clear_ioasic_dma_irq(irq);
 	printk(KERN_ERR "%s: DMA error\n", dev->name);
 	return IRQ_HANDLED;
 }