for multiple disk configurations, it was possible to get an interrupt for
a disk that hasn't been configured yet, thus indirecting a nil edma ptr.

Notes:
Mon Nov 27 11:27:13 EST 2006 geoff
    no need for the new memsets; the kernel malloc always
    zeroes memory.


Reference: /n/sources/patch/applied/mv50-spinup
Date: Mon Nov 20 16:37:02 CET 2006
Signed-off-by: quanstro@quanstro.net
Reviewed-by: geoff

--- /sys/src/9/pc/sdmv50xx.c	Mon Nov 20 16:34:27 2006
+++ /sys/src/9/pc/sdmv50xx.c	Mon Nov 20 16:34:19 2006
@@ -798,6 +798,8 @@
 	for(i=0; i<ctlr->ndrive; i++){
 		if(cause & (3<<(i*2+i/4))){
 			drive = &ctlr->drive[i];
+			if(drive->edma == 0)
+				continue;	// not ready yet.
 			ilock(drive);
 			updatedrive(drive, drive->edma->iec);
 			while(ctlr->chip[i/4].arb->ic & (0x0101 << (i%4))){
@@ -846,6 +848,8 @@
 			free(sdev);
 			continue;
 		}
+memset(sdev, 0, sizeof *sdev);
+memset(ctlr, 0, sizeof *ctlr);
 		io = p->mem[0].bar & ~0x0F;
 		mem = vmap(io, p->mem[0].size);
 		if(mem == 0){