linux-kernel - [PATCH 3/4] [USB] UASP: Reorganize stream id assignment

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Message-ID: <721095.19643.qm@web31806.mail.mud.yahoo.com>
Date:	Wed, 8 Dec 2010 15:56:22 -0800 (PST)
From:	Luben Tuikov <ltuikov@...oo.com>
To:	Greg KH <greg@...ah.com>, linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org
Subject: [PATCH 3/4] [USB] UASP: Reorganize stream id assignment

If the host controller reports more streams than
it actually supports and the device goes into flow
control due to an unsupported stream id, we can
now send a TMF with a stream id that the host
controller can handle.

Signed-off-by: Luben Tuikov <ltuikov@...oo.com>
---
 drivers/usb/storage/uasp.c |   35 ++++++++++++++++++++---------------
 1 files changed, 20 insertions(+), 15 deletions(-)

diff --git a/drivers/usb/storage/uasp.c b/drivers/usb/storage/uasp.c
index e5a26e9..40ee5a4 100644
--- a/drivers/usb/storage/uasp.c
+++ b/drivers/usb/storage/uasp.c
@@ -43,6 +43,10 @@ MODULE_PARM_DESC(MaxNumStreams, "\n"
 	"\tattached device and this value. Valid values are -1, default,\n"
 	"\tand 1 to 0xFFEF.");
 
+#define TMF_TAG          1
+#define CMD_UNTAGGED_TAG 2
+#define CMD_TAG_OFFS     3
+
 /* Information unit types
  */
 #define IU_CMD   1
@@ -189,7 +193,7 @@ static void uasp_sense(struct urb *urb, struct scsi_cmnd *cmd, u16 tag)
 		memcpy(cmd->sense_buffer, iu + IU_SENSE_LEN, slen);
 	}
 
-	if (tag == 1)
+	if (tag == CMD_UNTAGGED_TAG)
 		sdev->current_cmnd = NULL;
 	cmd->scsi_done(cmd);
 	usb_free_urb(urb);
@@ -267,10 +271,10 @@ static void uasp_stat_done(struct urb *urb)
 		return;
 	}
 
-	if (tag == 1)
+	if (tag == CMD_UNTAGGED_TAG)
 		cmd = sdev->current_cmnd;
-	else if (tag > 1)
-		cmd = scsi_find_tag(sdev, tag-2);
+	else if (tag >= CMD_TAG_OFFS)
+		cmd = scsi_find_tag(sdev, tag - CMD_TAG_OFFS);
 
 	if (cmd == NULL)
 		goto Out_no_cmd;
@@ -583,10 +587,10 @@ static int uasp_queuecommand(struct scsi_cmnd *cmd,
 	 * regardless of how many tags it supports.
 	 */
 	if (blk_rq_tagged(cmd->request)) {
-		cmdinfo->tag = cmd->request->tag + 2;
+		cmdinfo->tag = cmd->request->tag + CMD_TAG_OFFS;
 	} else if (sdev->current_cmnd == NULL) {
 		sdev->current_cmnd = cmd;
-		cmdinfo->tag = 1;
+		cmdinfo->tag = CMD_UNTAGGED_TAG;
 	} else {
 		cmd->result = DID_ABORT << 16;
 		goto Out_err;
@@ -643,7 +647,7 @@ static int uasp_alloc_tmf_urb(struct urb **urb, struct uasp_tport_info *tpinfo,
 	 * it for their own use, as well as being able to free it back
 	 * later. See the comment in uasp_set_max_cmds().
 	 */
-	tag = tpinfo->max_cmds + 2;
+	tag = TMF_TAG;
 
 	tiu[0] = IU_TMF;
 	tiu[2] = tag >> 8;
@@ -765,9 +769,9 @@ static int uasp_er_tmf(struct scsi_cmnd *cmd, u8 tmf)
 	int res;
 
 	if (sdev->current_cmnd == cmd)
-		tag = 1;
+		tag = CMD_UNTAGGED_TAG;
 	else
-		tag = cmd->request->tag + 2;
+		tag = cmd->request->tag + CMD_TAG_OFFS;
 
 	res = uasp_do_tmf(cmd, tmf, tag);
 
@@ -888,12 +892,13 @@ static int uasp_set_max_cmds(struct uasp_tport_info *tpinfo)
 {
 	int mc;
 
-	/* The range of tags generated by the block layer would be
-	 * [0, max_cmds-1], which is [0, num_streams-3]. Now reserve
-	 * stream 1 for untagged commands submitted to us and the last
-	 * usable stream id for a TMF to get the following stream id
-	 * assignment:
-	 * [1:untagged, [2, num_streams-1]:tagged, num_streams:TMF].
+	/* Define the following cmd tag assignment:
+	 * [1:TMF, 2:untagged, [3, num_streams]:tagged].
+	 * Thus there are num_streams-3+1 = num_streams-2 tags
+	 * for tagged commands. Report this number to the SCSI Core
+	 * as the number of maximum commands we can queue, thus
+	 * giving us a tag range [0, num_streams-3], which we
+	 * offset by 3 (CMD_TAG_OFFS).
 	 */
 	mc = tpinfo->num_streams - 2;
 	if (mc <= 0) {
-- 
1.7.0.1

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