linux-kernel - [PATCH v2] i2c: ocores: generate stop condition after timeout in polling mode

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Message-Id: <20230413093737.15303-1-matthias.schiffer@ew.tq-group.com>
Date:   Thu, 13 Apr 2023 11:37:37 +0200
From:   Matthias Schiffer <matthias.schiffer@...tq-group.com>
To:     Peter Korsgaard <peter@...sgaard.com>, Andrew Lunn <andrew@...n.ch>
Cc:     Federico Vaga <federico.vaga@...n.ch>,
        Wolfram Sang <wsa@...nel.org>, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux@...tq-group.com,
        Gregor Herburger <gregor.herburger@...group.com>,
        Matthias Schiffer <matthias.schiffer@...tq-group.com>
Subject: [PATCH v2] i2c: ocores: generate stop condition after timeout in polling mode

From: Gregor Herburger <gregor.herburger@...group.com>

In polling mode, no stop condition is generated after a timeout. This
causes SCL to remain low and thereby block the bus. If this happens
during a transfer it can cause slaves to misinterpret the subsequent
transfer and return wrong values.

To solve this, pass the ETIMEDOUT error up from ocores_process_polling()
instead of setting STATE_ERROR directly. The caller is adjusted to call
ocores_process_timeout() on error both in polling and in IRQ mode, which
will set STATE_ERROR and generate a stop condition.

Fixes: 69c8c0c0efa8 ("i2c: ocores: add polling interface")
Signed-off-by: Gregor Herburger <gregor.herburger@...group.com>
Signed-off-by: Matthias Schiffer <matthias.schiffer@...tq-group.com>
---

v2: style improvements based on feedback from Federico and Andrew. I went
    with a slightly different solution than Andrew suggested to avoid using
    the ret variable for two different kinds of returns.

 drivers/i2c/busses/i2c-ocores.c | 35 ++++++++++++++++++---------------
 1 file changed, 19 insertions(+), 16 deletions(-)

diff --git a/drivers/i2c/busses/i2c-ocores.c b/drivers/i2c/busses/i2c-ocores.c
index a0af027db04c1..2e575856c5cd5 100644
--- a/drivers/i2c/busses/i2c-ocores.c
+++ b/drivers/i2c/busses/i2c-ocores.c
@@ -342,18 +342,18 @@ static int ocores_poll_wait(struct ocores_i2c *i2c)
  * ocores_isr(), we just add our polling code around it.
  *
  * It can run in atomic context
+ *
+ * Return: 0 on success, -ETIMEDOUT on timeout
  */
-static void ocores_process_polling(struct ocores_i2c *i2c)
+static int ocores_process_polling(struct ocores_i2c *i2c)
 {
-	while (1) {
-		irqreturn_t ret;
-		int err;
+	irqreturn_t ret;
+	int err = 0;
 
+	while (1) {
 		err = ocores_poll_wait(i2c);
-		if (err) {
-			i2c->state = STATE_ERROR;
+		if (err)
 			break; /* timeout */
-		}
 
 		ret = ocores_isr(-1, i2c);
 		if (ret == IRQ_NONE)
@@ -364,13 +364,15 @@ static void ocores_process_polling(struct ocores_i2c *i2c)
 					break;
 		}
 	}
+
+	return err;
 }
 
 static int ocores_xfer_core(struct ocores_i2c *i2c,
 			    struct i2c_msg *msgs, int num,
 			    bool polling)
 {
-	int ret;
+	int ret = 0;
 	u8 ctrl;
 
 	ctrl = oc_getreg(i2c, OCI2C_CONTROL);
@@ -388,15 +390,16 @@ static int ocores_xfer_core(struct ocores_i2c *i2c,
 	oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_START);
 
 	if (polling) {
-		ocores_process_polling(i2c);
+		ret = ocores_process_polling(i2c);
 	} else {
-		ret = wait_event_timeout(i2c->wait,
-					 (i2c->state == STATE_ERROR) ||
-					 (i2c->state == STATE_DONE), HZ);
-		if (ret == 0) {
-			ocores_process_timeout(i2c);
-			return -ETIMEDOUT;
-		}
+		if (wait_event_timeout(i2c->wait,
+				       (i2c->state == STATE_ERROR) ||
+				       (i2c->state == STATE_DONE), HZ) == 0)
+			ret = -ETIMEDOUT;
+	}
+	if (ret) {
+		ocores_process_timeout(i2c);
+		return ret;
 	}
 
 	return (i2c->state == STATE_DONE) ? num : -EIO;
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