ar71xx: fix a wifi card stability issue

when we receive a pci/ahb interrupt, we need to flush pending data for dma
from the device, otherwise the tx path may get stuck if the completion flag
of the dma descriptor is not updated at the time the tx interrupt arrives.

SVN-Revision: 21143

target/linux/ar71xx/files/arch/mips/ar71xx/irq.c

@@ -21,6 +21,8 @@
 
 #include <asm/mach-ar71xx/ar71xx.h>
 
+static int ip2_flush_reg;
+
 static void ar71xx_gpio_irq_dispatch(void)
 {
 	void __iomem *base = ar71xx_gpio_base;
@@ -239,8 +241,17 @@ asmlinkage void plat_irq_dispatch(void)
 	if (pending & STATUSF_IP7)
 		do_IRQ(AR71XX_CPU_IRQ_TIMER);
 
-	else if (pending & STATUSF_IP2)
+	else if (pending & STATUSF_IP2) {
+		/*
+		 * This IRQ is meant for a PCI device. Drivers for PCI devices
+		 * typically allocate coherent DMA memory for the descriptor
+		 * ring, however the DMA controller may still have some
+		 * unsynchronized data in the FIFO.
+		 * Issue a flush here to ensure that the driver sees the update.
+		 */
+		ar71xx_ddr_flush(ip2_flush_reg);
 		do_IRQ(AR71XX_CPU_IRQ_IP2);
+	}
 
 	else if (pending & STATUSF_IP4)
 		do_IRQ(AR71XX_CPU_IRQ_GE0);
@@ -260,6 +271,20 @@ asmlinkage void plat_irq_dispatch(void)
 
 void __init arch_init_irq(void)
 {
+	switch(ar71xx_soc) {
+	case AR71XX_SOC_AR7240:
+	case AR71XX_SOC_AR7241:
+	case AR71XX_SOC_AR7242:
+		ip2_flush_reg = AR724X_DDR_REG_FLUSH_PCIE;
+		break;
+	case AR71XX_SOC_AR9130:
+	case AR71XX_SOC_AR9132:
+		ip2_flush_reg = AR91XX_DDR_REG_FLUSH_WMAC;
+		break;
+	default:
+		ip2_flush_reg = AR71XX_DDR_REG_FLUSH_PCI;
+		break;
+	}
 	mips_cpu_irq_init();
 
 	ar71xx_misc_irq_init();