> As before, no problems using the sda hard disk (which is the boot drive):
> everything works reliably until I touch the cdrom drive.

A little quiet contemplation and gnome number 387 suggests trying the following
(and providing more detailed information such as the last message printed before
the DMA message). Stuff a BUG() before the panic in BAD_DMA (aha1542.c) if 
needed
to get a good trace.

Please report success/failure/change.

--- drivers/scsi/sr_ioctl.c~    2007-04-27 22:53:33.885035256 +0100
+++ drivers/scsi/sr_ioctl.c     2007-04-27 22:53:33.885035256 +0100
@@ -187,9 +187,10 @@
        struct scsi_sense_hdr sshdr;
        int result, err = 0, retries = 0;
        struct request_sense *sense = cgc->sense;
-
+       void *zebedee = cgc->buffer;
+       
        SDev = cd->device;
-
+       
        if (!sense) {
                sense = kmalloc(SCSI_SENSE_BUFFERSIZE, GFP_KERNEL);
                if (!sense) {
@@ -197,7 +198,22 @@
                        goto out;
                }
        }
-
+       
+       if (cgc->buflen && cd->device->host->unchecked_isa_dma) {
+               switch(cgc->data_direction) {
+                       case DMA_NONE:
+                               break;
+                       case DMA_FROM_DEVICE:
+                       case DMA_TO_DEVICE: /* Boing!!!! said Zebedee */
+                               zebedee = kmalloc(cgc->buflen, 
GFP_KERNEL|GFP_DMA);
+                               if (zebedee ==NULL) {
+                                       err = -ENOMEM;
+                                       goto out;
+                               }
+               }
+               if (cgc->data_direction == DMA_TO_DEVICE)
+                       memcpy(zebedee, cgc->buffer, cgc->buflen);
+       }
       retry:
        if (!scsi_block_when_processing_errors(SDev)) {
                err = -ENODEV;
@@ -206,10 +222,13 @@
 
        memset(sense, 0, sizeof(*sense));
        result = scsi_execute(SDev, cgc->cmd, cgc->data_direction,
-                             cgc->buffer, cgc->buflen, (char *)sense,
+                             zebedee, cgc->buflen, (char *)sense,
                              cgc->timeout, IOCTL_RETRIES, 0);
 
        scsi_normalize_sense((char *)sense, sizeof(*sense), &sshdr);
+       
+       if (zebedeee != cgc->buffer && cgc->data_direction == DMA_FROM_DEVICE)
+               memcpy(cgc->buffer, zebedee, cgc->buflen);
 
        /* Minimal error checking.  Ignore cases we know about, and report the 
rest. */
        if (driver_byte(result) != 0) {
-
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