From mboxrd@z Thu Jan  1 00:00:00 1970
From: Albert Lee <albertcc@tw.ibm.com>
Subject: Re: [PATCH 1/1] libata-dev-2.6: pdc2027x ATAPI DMA fix
Date: Wed, 27 Apr 2005 16:55:57 +0800
Message-ID: <426F539D.3090605@tw.ibm.com>
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To: Jeff Garzik <jgarzik@pobox.com>
Cc: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>, Doug Maxey <dwm@maxeymade.com>, Linux IDE <linux-ide@vger.kernel.org>, Jens Axboe <axboe@suse.de>

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Hi Jeff,

Revised pdc2027x: pdc2027x ATAPI DMA fix.
(Please ignore the previous patch.)

Problem:
The previous (request_bufflen % 256) ATAPI DMA rule still fails and
causes timeout in some case.

Changes:
- Only turn on pdc2027x ATAPI DMA for READ/WRITE.

The additional (request_bufflen % 1024 == 0) check in the previous patch is
not necessary. Since most ATAPI devices has 512 bytes or 2048 bytes sector size,
it should be safe for ATAPI DMA. Thanks Jens for the advice.

Attached please find the revised patch against the libata-dev-2.6 tree for your
review. Thanks.

Albert

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--- linux-2.6.5-SLES9_SP2_BRANCH_20050418161416/drivers/scsi/pata_pdc2027x.c.ori	2005-04-19 15:34:15.000000000 +0800
+++ linux-2.6.5-SLES9_SP2_BRANCH_20050418161416/drivers/scsi/pata_pdc2027x.c	2005-04-26 21:44:18.849971712 +0800
@@ -29,7 +29,7 @@
 #include <asm/io.h>
 
 #define DRV_NAME	"pata_pdc2027x"
-#define DRV_VERSION	"0.60"
+#define DRV_VERSION	"0.61"
 #undef PDC_DEBUG
 
 #ifdef PDC_DEBUG
@@ -445,11 +445,24 @@
 static int pdc2027x_check_atapi_dma(struct ata_queued_cmd *qc)
 {
 	struct scsi_cmnd *cmd = qc->scsicmd;
-	int rc = 0;
+	u8 *scsicmd = cmd->cmnd;
+	int rc = 1; /* atapi dma off by default */
 
-	/* pdc2027x can only do ATAPI DMA for specific buffer size */
-	if (cmd->request_bufflen % 256)
-		rc = 1;
+	switch (scsicmd[0]) {
+	case READ_6:
+	case READ_10:
+	case READ_12:
+	case READ_16:
+
+	case WRITE_6:
+	case WRITE_10:
+	case WRITE_12:
+	case WRITE_16:
+		rc = 0;
+		break;
+	default:
+		;
+	}
 
 	return rc;
 }

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