patch-2.4.13 linux/arch/arm/kernel/dma-isa.c

• Lines: 28
• Date: Thu Oct 11 09:04:57 2001
• Orig file: v2.4.12/linux/arch/arm/kernel/dma-isa.c
• Orig date: Mon Sep 18 15:15:24 2000

diff -u --recursive --new-file v2.4.12/linux/arch/arm/kernel/dma-isa.c linux/arch/arm/kernel/dma-isa.c
@@ -148,17 +148,22 @@
 
 void __init isa_init_dma(dma_t *dma)
 {
-	int dmac_found;
-
+	/*
+	 * Try to autodetect presence of an ISA DMA controller.
+	 * We do some minimal initialisation, and check that
+	 * channel 0's DMA address registers are writeable.
+	 */
 	outb(0xff, 0x0d);
 	outb(0xff, 0xda);
 
+	/*
+	 * Write high and low address, and then read them back
+	 * in the same order.
+	 */
 	outb(0x55, 0x00);
 	outb(0xaa, 0x00);
 
-	dmac_found = inb(0x00) == 0x55 && inb(0x00) == 0xaa;
-
-	if (dmac_found) {
+	if (inb(0) == 0x55 && inb(0) == 0xaa) {
 		int channel, i;
 
 		for (channel = 0; channel < 8; channel++) {