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Subject[Patch] SCSI: Retrieve Cache Mode Using SG_ATA_16 if normal routine fails
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SCSI: Retrieve Cache Mode Using SG_ATA_16 if normal routine fails

It has been observed that a number of USB HDD's do not respond correctly
to SCSI mode sense command(retrieve caching pages) which results in their
Write Cache being discarded by queue requests i.e., WCE if left set to
'0'(disabled). So, in order to identify the devices correctly - give it
a last try using SG_ATA_16 after failure from normal routine.

Signed-off-by: Amit Sahrawat <amit.sahrawat83@gmail.com>

diff -Nurp linux-Orig/drivers/scsi/sd.c linux-Updated/drivers/scsi/sd.c
--- linux-Orig/drivers/scsi/sd.c 2011-10-11 11:02:48.000000000 +0530
+++ linux-Updated/drivers/scsi/sd.c 2011-10-11 11:10:09.000000000 +0530
@@ -56,6 +56,7 @@
#include <asm/uaccess.h>
#include <asm/unaligned.h>

+#include <scsi/sg.h>
#include <scsi/scsi.h>
#include <scsi/scsi_cmnd.h>
#include <scsi/scsi_dbg.h>
@@ -134,6 +135,58 @@ static const char *sd_cache_types[] = {
"write back, no read (daft)"
};

+/* Relevant Structure and Function to be used to Retrieve
+ * Caching Information from USB HDD - this is picked from
+ * source code of 'hdparm'
+ *
+ *
+ * Definitions and structures for use with SG_IO + ATA_16:
+ * */
+#define SG_ATA_16 0x85
+#define SG_ATA_16_LEN 16
+
+#define ATA_OP_IDENTIFY 0xec
+
+/*
+ * Some useful ATA register bits
+ */
+enum {
+ ATA_USING_LBA = (1 << 6),
+ ATA_STAT_DRQ = (1 << 3),
+ ATA_STAT_ERR = (1 << 0),
+};
+
+struct ata_lba_regs {
+ __u8 feat;
+ __u8 nsect;
+ __u8 lbal;
+ __u8 lbam;
+ __u8 lbah;
+};
+struct ata_tf {
+ __u8 dev;
+ __u8 command;
+ __u8 error;
+ __u8 status;
+ __u8 is_lba48;
+ struct ata_lba_regs lob;
+ struct ata_lba_regs hob;
+};
+
+__u64 tf_to_lba (struct ata_tf *tf)
+{
+ __u32 lba24, lbah;
+ __u64 lba64;
+
+ lba24 = (tf->lob.lbah << 16) | (tf->lob.lbam << 8) | (tf->lob.lbal);
+ if (tf->is_lba48)
+ lbah = (tf->hob.lbah << 16) | (tf->hob.lbam << 8) |
(tf->hob.lbal);
+ else
+ lbah = (tf->dev & 0x0f);
+ lba64 = (((__u64)lbah) << 24) | (__u64)lba24;
+ return lba64;
+}
+
static ssize_t
sd_store_cache_type(struct device *dev, struct device_attribute *attr,
const char *buf, size_t count)
@@ -1839,6 +1892,18 @@ sd_read_cache_type(struct scsi_disk *sdk
int old_rcd = sdkp->RCD;
int old_dpofua = sdkp->DPOFUA;

+ struct ata_tf tf;
+ struct sg_io_hdr io_hdr;
+ unsigned char cdb[SG_ATA_16_LEN] = {0};
+ unsigned char sb[32] = {0};
+ unsigned char buf[512] = {0};
+ unsigned short wce_word = 0;
+ void *data_cmd = buf;
+
+ memset(cdb, 0, SG_ATA_16_LEN);
+ memset(&tf, 0, sizeof(struct ata_tf));
+ memset(&io_hdr, 0, sizeof(struct sg_io_hdr));
+
first_len = 4;
if (sdp->skip_ms_page_8) {
if (sdp->type == TYPE_RBC)
@@ -1961,7 +2026,6 @@ Page_found:
sdkp->DPOFUA ? "supports DPO and FUA"
: "doesn't support DPO or FUA");

- return;
}

bad_sense:
@@ -1974,8 +2038,64 @@ bad_sense:
sd_printk(KERN_ERR, sdkp, "Asking for cache data failed\n");

defaults:
- sd_printk(KERN_ERR, sdkp, "Assuming drive cache: write through\n");
- sdkp->WCE = 0;
+ if (sdkp->WCE)
+ return;
+ else {
+ sd_printk(KERN_ERR, sdkp, "Normal Routine Failed: Trying ATA_16\n");
+
+ /* The below are necessary parameters which are to set - in order
+ to make use of ATA_OP_IDENTIFY command */
+ tf.lob.lbal = 0;
+ tf.lob.lbam = 0;
+ tf.lob.lbah = 0;
+ tf.lob.nsect = 1; //Number of Sectors to Read
+ tf.lob.feat = 0;
+
+ /* Command Descriptor Block For SCSI */
+ cdb[0] = SG_ATA_16;
+ cdb[1] = 0x08;
+ cdb[2] = 0x0e;
+ cdb[6] = 0x01; //No. of Sectors To Read
+ cdb[13] = ATA_USING_LBA;
+ cdb[14] = ATA_OP_IDENTIFY;
+
+ io_hdr.cmd_len = SG_ATA_16_LEN;
+ io_hdr.interface_id = SG_INTERFACE_ID_ORIG;
+ io_hdr.mx_sb_len= sizeof(sb);
+ io_hdr.dxfer_direction = SG_DXFER_FROM_DEV;
+ io_hdr.dxfer_len = sizeof(buf);
+ io_hdr.dxferp = data_cmd;
+ io_hdr.cmdp = cdb;
+ io_hdr.sbp = sb;
+ io_hdr.pack_id = tf_to_lba(&tf);
+ io_hdr.timeout = 0;
+
+ if (!scsi_cmd_ioctl(sdkp->disk->queue, sdkp->disk,
O_RDONLY|O_NONBLOCK, SG_IO, &io_hdr))
+ {
+#if 0
+#define DUMP_BYTES_BUFFER(x...) printk( x )
+ int i;
+ for (i = 0; i < 32; i++)
+ DUMP_BYTES_BUFFER(" %02x", sb[i]);
+ DUMP_BYTES_BUFFER("\n");
+ for (i = 0; i < 512; i++)
+ DUMP_BYTES_BUFFER(" %02x", buf[i]);
+ DUMP_BYTES_BUFFER("\n");
+ printk(KERN_ERR"82 - [0x%x], 85 -
[0x%x]\n",((unsigned short*)data_cmd)[82],((unsigned
short*)data_cmd)[85]);
+#endif
+ /* '6th' Bit in Word 85 Corresponds to Write Cache being Enabled/disabled*/
+ wce_word = le16_to_cpu(((unsigned short*)data_cmd)[85]);
+ if (wce_word & 0x20) {
+ sdkp->WCE = 1;
+ sd_printk(KERN_NOTICE, sdkp, "Write Cache Enabled
after ATA_16 response\n");
+ } else
+ goto write_through;
+ } else {
+write_through:
+ sd_printk(KERN_ERR, sdkp, "Assuming drive cache: write through\n");
+ sdkp->WCE = 0;
+ }
+ }
sdkp->RCD = 0;
sdkp->DPOFUA = 0;
}

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