linux-kernel - [PATCH v2 05/13] i2c: qup: schedule EOT and FLUSH tags at the end of transfer

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Date:   Mon, 12 Mar 2018 18:44:54 +0530
From:   Abhishek Sahu <absahu@...eaurora.org>
To:     Andy Gross <andy.gross@...aro.org>,
        Wolfram Sang <wsa@...-dreams.de>
Cc:     David Brown <david.brown@...aro.org>,
        Sricharan R <sricharan@...eaurora.org>,
        Austin Christ <austinwc@...eaurora.org>,
        linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        Abhishek Sahu <absahu@...eaurora.org>
Subject: [PATCH v2 05/13] i2c: qup: schedule EOT and FLUSH tags at the end of transfer

The role of FLUSH and EOT tag is to flush already scheduled
descriptors in BAM HW in case of error. EOT is required only
when descriptors are scheduled in RX FIFO. If all the messages
are WRITE, then only FLUSH tag will be used.

A single BAM transfer can have multiple read and write messages.
The EOT and FLUSH tags should be scheduled at the end of BAM HW
descriptors. Since the READ and WRITE can be present in any order
so for some of the cases, these tags are not being written
correctly.

Following is one of the example

   READ, READ, READ, READ

Currently EOT and FLUSH tags are being written after each READ.
If QUP gets NACK for first READ itself, then flush will be
triggered. It will look for first FLUSH tag in TX FIFO and will
stop there so only descriptors for first READ descriptors be
flushed. All the scheduled descriptors should be cleared to
generate BAM DMA completion.

Now this patch is scheduling FLUSH and EOT only once after all the
descriptors. So, flush will clear all the scheduled descriptors and
BAM will generate the completion interrupt.

Signed-off-by: Abhishek Sahu <absahu@...eaurora.org>
---

* Changes from v1:

1. Modified commit message with more details

 drivers/i2c/busses/i2c-qup.c | 39 ++++++++++++++++++++++++---------------
 1 file changed, 24 insertions(+), 15 deletions(-)

diff --git a/drivers/i2c/busses/i2c-qup.c b/drivers/i2c/busses/i2c-qup.c
index d970458..b2e8f57 100644
--- a/drivers/i2c/busses/i2c-qup.c
+++ b/drivers/i2c/busses/i2c-qup.c
@@ -551,7 +551,7 @@ static int qup_i2c_set_tags_smb(u16 addr, u8 *tags, struct qup_i2c_dev *qup,
 }
 
 static int qup_i2c_set_tags(u8 *tags, struct qup_i2c_dev *qup,
-			    struct i2c_msg *msg,  int is_dma)
+			    struct i2c_msg *msg)
 {
 	u16 addr = i2c_8bit_addr_from_msg(msg);
 	int len = 0;
@@ -592,11 +592,6 @@ static int qup_i2c_set_tags(u8 *tags, struct qup_i2c_dev *qup,
 	else
 		tags[len++] = data_len;
 
-	if ((msg->flags & I2C_M_RD) && last && is_dma) {
-		tags[len++] = QUP_BAM_INPUT_EOT;
-		tags[len++] = QUP_BAM_FLUSH_STOP;
-	}
-
 	return len;
 }
 
@@ -605,7 +600,7 @@ static int qup_i2c_issue_xfer_v2(struct qup_i2c_dev *qup, struct i2c_msg *msg)
 	int data_len = 0, tag_len, index;
 	int ret;
 
-	tag_len = qup_i2c_set_tags(qup->blk.tags, qup, msg, 0);
+	tag_len = qup_i2c_set_tags(qup->blk.tags, qup, msg);
 	index = msg->len - qup->blk.data_len;
 
 	/* only tags are written for read */
@@ -701,7 +696,7 @@ static int qup_i2c_bam_do_xfer(struct qup_i2c_dev *qup, struct i2c_msg *msg,
 			while (qup->blk.pos < blocks) {
 				tlen = (i == (blocks - 1)) ? rem : limit;
 				tags = &qup->start_tag.start[off + len];
-				len += qup_i2c_set_tags(tags, qup, msg, 1);
+				len += qup_i2c_set_tags(tags, qup, msg);
 				qup->blk.data_len -= tlen;
 
 				/* scratch buf to read the start and len tags */
@@ -729,17 +724,11 @@ static int qup_i2c_bam_do_xfer(struct qup_i2c_dev *qup, struct i2c_msg *msg,
 				return ret;
 
 			off += len;
-			/* scratch buf to read the BAM EOT and FLUSH tags */
-			ret = qup_sg_set_buf(&qup->brx.sg[rx_cnt++],
-					     &qup->brx.tag.start[0],
-					     2, qup, DMA_FROM_DEVICE);
-			if (ret)
-				return ret;
 		} else {
 			while (qup->blk.pos < blocks) {
 				tlen = (i == (blocks - 1)) ? rem : limit;
 				tags = &qup->start_tag.start[off + tx_len];
-				len = qup_i2c_set_tags(tags, qup, msg, 1);
+				len = qup_i2c_set_tags(tags, qup, msg);
 				qup->blk.data_len -= tlen;
 
 				ret = qup_sg_set_buf(&qup->btx.sg[tx_cnt++],
@@ -779,6 +768,26 @@ static int qup_i2c_bam_do_xfer(struct qup_i2c_dev *qup, struct i2c_msg *msg,
 		msg++;
 	}
 
+	/* schedule the EOT and FLUSH I2C tags */
+	len = 1;
+	if (rx_cnt) {
+		qup->btx.tag.start[0] = QUP_BAM_INPUT_EOT;
+		len++;
+
+		/* scratch buf to read the BAM EOT and FLUSH tags */
+		ret = qup_sg_set_buf(&qup->brx.sg[rx_cnt++],
+				     &qup->brx.tag.start[0],
+				     2, qup, DMA_FROM_DEVICE);
+		if (ret)
+			return ret;
+	}
+
+	qup->btx.tag.start[len - 1] = QUP_BAM_FLUSH_STOP;
+	ret = qup_sg_set_buf(&qup->btx.sg[tx_cnt++], &qup->btx.tag.start[0],
+			     len, qup, DMA_TO_DEVICE);
+	if (ret)
+		return ret;
+
 	txd = dmaengine_prep_slave_sg(qup->btx.dma, qup->btx.sg, tx_cnt,
 				      DMA_MEM_TO_DEV,
 				      DMA_PREP_INTERRUPT | DMA_PREP_FENCE);
-- 
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