[PATCH] ide-scsi driver starts DMA too soon

[PATCH] ide-scsi driver starts DMA too soon

[Khalid Aziz]

ide-scsi driver starts DMA as soon as it writes the ATAPI PACKET command
in command register and before sending the ATAPI command. This will
cause problems on many drives. Right way to do it is to start DMA after
sending the ATAPI command. I am attaching a patch that fixes this. This
patch will allow many more CD-RW drives to work reliably in DMA mode 
than do today.

Marcelo, please apply.

--
Khalid

====================================================================
Khalid Aziz                                Linux and Open Source Lab
(970)898-9214                                        Hewlett-Packard
khalid@hp.com                                       Fort Collins, CO


-----------CUT HERE-------------CUT HERE-------------CUT HERE-----------
--- linux-2.4.19/drivers/scsi/ide-scsi.c	Fri Aug  2 18:39:44 2002
+++ linux-2.4.19.cd_dma/drivers/scsi/ide-scsi.c	Fri Nov  1 16:31:30 2002
@@ -397,6 +397,8 @@
 	idescsi_pc_t *pc = scsi->pc;
 	byte ireason;
 	ide_startstop_t startstop;
+	struct request *rq = pc->rq;
+	int dma_ok = 0;
 
 	if (ide_wait_stat (&startstop,drive,DRQ_STAT,BUSY_STAT,WAIT_READY)) {
 		printk (KERN_ERR "ide-scsi: Strange, packet command initiated yet DRQ isn't asserted\n");
@@ -407,8 +409,14 @@
 		printk (KERN_ERR "ide-scsi: (IO,CoD) != (0,1) while issuing a packet command\n");
 		return ide_do_reset (drive);
 	}
+	if (drive->using_dma && rq->bh)
+		dma_ok=!HWIF(drive)->dmaproc(test_bit (PC_WRITING, &pc->flags) ? ide_dma_write : ide_dma_read, drive);
 	ide_set_handler(drive, &idescsi_pc_intr, get_timeout(pc), NULL);	/* Set the interrupt routine */
 	atapi_output_bytes (drive, scsi->pc->c, 12);			/* Send the actual packet */
+	if (dma_ok) {
+		set_bit (PC_DMA_IN_PROGRESS, &pc->flags);
+		(void) (HWIF(drive)->dmaproc(ide_dma_begin, drive));
+	}
 	return ide_started;
 }
 
@@ -437,10 +445,6 @@
 	OUT_BYTE (bcount >> 8,IDE_BCOUNTH_REG);
 	OUT_BYTE (bcount & 0xff,IDE_BCOUNTL_REG);
 
-	if (dma_ok) {
-		set_bit (PC_DMA_IN_PROGRESS, &pc->flags);
-		(void) (HWIF(drive)->dmaproc(ide_dma_begin, drive));
-	}
 	if (test_bit (IDESCSI_DRQ_INTERRUPT, &scsi->flags)) {
 		ide_set_handler (drive, &idescsi_transfer_pc, get_timeout(pc), NULL);
 		OUT_BYTE (WIN_PACKETCMD, IDE_COMMAND_REG);		/* Issue the packet command */

Re: [PATCH] ide-scsi driver starts DMA too soon

[Alan Cox]

On Fri, 2002-11-01 at 23:39, Khalid Aziz wrote:
> ide-scsi driver starts DMA as soon as it writes the ATAPI PACKET command
> in command register and before sending the ATAPI command. This will
> cause problems on many drives. Right way to do it is to start DMA after
> sending the ATAPI command. I am attaching a patch that fixes this. This
> patch will allow many more CD-RW drives to work reliably in DMA mode 
> than do today.
> 
> Marcelo, please apply.

Marcelo this is in 2.5, and 2.4-ac. Khalid is certainly correct although
making such a change in -rc rather than a pre does mean it wants extra
thought

Re: [PATCH] ide-scsi driver starts DMA too soon

[Marcelo Tosatti]

On 2 Nov 2002, Alan Cox wrote:

> On Fri, 2002-11-01 at 23:39, Khalid Aziz wrote:
> > ide-scsi driver starts DMA as soon as it writes the ATAPI PACKET command
> > in command register and before sending the ATAPI command. This will
> > cause problems on many drives. Right way to do it is to start DMA after
> > sending the ATAPI command. I am attaching a patch that fixes this. This
> > patch will allow many more CD-RW drives to work reliably in DMA mode
> > than do today.
> >
> > Marcelo, please apply.
>
> Marcelo this is in 2.5, and 2.4-ac. Khalid is certainly correct although
> making such a change in -rc rather than a pre does mean it wants extra
> thought

I prefer being safe and saving this one for 2.4.21-pre.

Thanks Khalid!