linux-kernel - [PATCH v3 1/1] i3c: Add fallback method for GETMXDS CCC

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Message-ID: <20231114085525.6271-2-joshua.yeong@starfivetech.com>
Date:   Tue, 14 Nov 2023 16:55:25 +0800
From:   Joshua Yeong <joshua.yeong@...rfivetech.com>
To:     <alexandre.belloni@...tlin.com>, <miquel.raynal@...tlin.com>
CC:     <linux-i3c@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        "Joshua Yeong" <joshua.yeong@...rfivetech.com>
Subject: [PATCH v3 1/1] i3c: Add fallback method for GETMXDS CCC

Some I3C hardware will report error when an incorrect length is received from
device. GETMXDS CCC are available 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. So in case sending GETMXDS CCC format 2 resulted
in a failure, try sending GETMXDS CCC format 1 instead.

Signed-off-by: Joshua Yeong <joshua.yeong@...rfivetech.com>
---
 drivers/i3c/master.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
index 95caa162706f..718b643cb54d 100644
--- a/drivers/i3c/master.c
+++ b/drivers/i3c/master.c
@@ -1130,8 +1130,16 @@ static int i3c_master_getmxds_locked(struct i3c_master_controller *master,
 
 	i3c_ccc_cmd_init(&cmd, true, I3C_CCC_GETMXDS, &dest, 1);
 	ret = i3c_master_send_ccc_cmd_locked(master, &cmd);
-	if (ret)
-		goto out;
+	if (ret) {
+		/*
+		 * Retry when the device does not support max read turnaround
+		 * while expecting shorter length from this CCC command.
+		 */
+		dest->payload.len -= 3;
+		ret = i3c_master_send_ccc_cmd_locked(master, &cmd);
+		if (ret)
+			goto out;
+	}
 
 	if (dest.payload.len != 2 && dest.payload.len != 5) {
 		ret = -EIO;
-- 
2.25.1