linux-kernel - [PATCH 1/1] i3c: Add fallback method for GETMXDS CCC

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Date:   Mon, 11 Sep 2023 16:24:56 +0800
From:   Joshua Yeong <joshua.yeong@...rfivetech.com>
To:     <alexandre.belloni@...tlin.com>
CC:     <linux-i3c@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        "Joshua Yeong" <joshua.yeong@...rfivetech.com>
Subject: [PATCH 1/1] i3c: Add fallback method for GETMXDS CCC

Some I3C hardware will report error when incorrect length is received from
device. GETMXDS CCC are availble in 2 formats; without turnaround time (format
1) and with turnaround time (format 2). There is no mechanics to determine which
format is supported by device. In case sending GETMXDS CCC format 2 resulted
failure, try sending GETMXDS CCC format 1 instead.

Signed-off-by: Joshua Yeong <joshua.yeong@...rfivetech.com>
---
 drivers/i3c/master.c    | 33 ++++++++++++++++++++++++++++-----
 include/linux/i3c/ccc.h | 17 +++++++++++++++--
 2 files changed, 43 insertions(+), 7 deletions(-)

diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
index 87283e4a4607..084f64bef155 100644
--- a/drivers/i3c/master.c
+++ b/drivers/i3c/master.c
@@ -1088,10 +1088,37 @@ static int i3c_master_getmxds_locked(struct i3c_master_controller *master,
 				     struct i3c_device_info *info)
 {
 	struct i3c_ccc_getmxds *getmaxds;
+	struct i3c_ccc_getmxds_turnaround *getmaxds_ta;
 	struct i3c_ccc_cmd_dest dest;
 	struct i3c_ccc_cmd cmd;
 	int ret;
 
+	getmaxds_ta = i3c_ccc_cmd_dest_init(&dest, info->dyn_addr,
+					 sizeof(*getmaxds_ta));
+	if (!getmaxds_ta)
+		return -ENOMEM;
+
+	i3c_ccc_cmd_init(&cmd, true, I3C_CCC_GETMXDS, &dest, 1);
+	ret = i3c_master_send_ccc_cmd_locked(master, &cmd);
+	if (ret) {
+		goto alternative;
+	}
+
+	if (dest.payload.len != 2 && dest.payload.len != 5) {
+		ret = -EIO;
+		goto out;
+	}
+
+	info->max_read_ds = getmaxds_ta->maxrd;
+	info->max_write_ds = getmaxds_ta->maxwr;
+	if (dest.payload.len == 5)
+		info->max_read_turnaround = getmaxds_ta->maxrdturn[0] |
+					    ((u32)getmaxds_ta->maxrdturn[1] << 8) |
+					    ((u32)getmaxds_ta->maxrdturn[2] << 16);
+
+alternative:
+	i3c_ccc_cmd_dest_cleanup(&dest);
+
 	getmaxds = i3c_ccc_cmd_dest_init(&dest, info->dyn_addr,
 					 sizeof(*getmaxds));
 	if (!getmaxds)
@@ -1102,17 +1129,13 @@ static int i3c_master_getmxds_locked(struct i3c_master_controller *master,
 	if (ret)
 		goto out;
 
-	if (dest.payload.len != 2 && dest.payload.len != 5) {
+	if (dest.payload.len != 2) {
 		ret = -EIO;
 		goto out;
 	}
 
 	info->max_read_ds = getmaxds->maxrd;
 	info->max_write_ds = getmaxds->maxwr;
-	if (dest.payload.len == 5)
-		info->max_read_turnaround = getmaxds->maxrdturn[0] |
-					    ((u32)getmaxds->maxrdturn[1] << 8) |
-					    ((u32)getmaxds->maxrdturn[2] << 16);
 
 out:
 	i3c_ccc_cmd_dest_cleanup(&dest);
diff --git a/include/linux/i3c/ccc.h b/include/linux/i3c/ccc.h
index ad59a4ae60d1..50ed41d4d5a1 100644
--- a/include/linux/i3c/ccc.h
+++ b/include/linux/i3c/ccc.h
@@ -269,14 +269,27 @@ enum i3c_tsco {
 #define I3C_CCC_MAX_SDR_FSCL(x)		((x) & I3C_CCC_MAX_SDR_FSCL_MASK)
 
 /**
- * struct i3c_ccc_getmxds - payload passed to GETMXDS CCC
+ * struct i3c_ccc_getmxds - payload passed to GETMXDS CCC without turnaround
+ * (format 1)
+ *
+ * @maxwr: write limitations
+ * @maxrd: read limitations
+ */
+struct i3c_ccc_getmxds {
+	u8 maxwr;
+	u8 maxrd;
+} __packed;
+
+/**
+ * struct i3c_ccc_getmxds_ta - payload passed to GETMXDS CCC with turnaround
+ * (format 2)
  *
  * @maxwr: write limitations
  * @maxrd: read limitations
  * @maxrdturn: maximum read turn-around expressed micro-seconds and
  *	       little-endian formatted
  */
-struct i3c_ccc_getmxds {
+struct i3c_ccc_getmxds_turnaround {
 	u8 maxwr;
 	u8 maxrd;
 	u8 maxrdturn[3];
-- 
2.25.1