linux-kernel - [PATCH v6 2/2] i2c: muxes: pca954x: Reset if (de)select fails

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Message-Id: <20250514122226.3267855-3-wojciech.siudy@nokia.com>
Date: Wed, 14 May 2025 14:22:26 +0200
From: Wojciech Siudy <wojciech.siudy@...ia.com>
To: linux-kernel@...r.kernel.org,
	linux-i2c@...r.kernel.org
Cc: andi.shyti@...nel.org,
	mariusz.madej@...ia.com,
	Wojciech Siudy <wojciech.siudy@...ia.com>
Subject: [PATCH v6 2/2] i2c: muxes: pca954x: Reset if (de)select fails

If the channel selection or deselection times out, it indicates
a failure in the mux's I2C subsystem. Without sending a reset pulse,
a power-on-reset of the entire device would be required to restore
communication.

The datasheet specifies a minimum hold time of 4 ns for the reset
pulse, but due to the path's capacitance and themux having its own
clock, it is recommended to extend this to approximately 1 us.

Since reset controller is used, there is no need to take care of other
devices sharing the same reset line.

Signed-off-by: Wojciech Siudy <wojciech.siudy@...ia.com>
---
Changelog:
v2:
  * Removed mail header from the commit log
  * Decreased reset pulse hold time from 10 to 1 ms
v3:
  * Make this functionality enabled by appropriate property in
    devicetree
v4:
  * Fix missing condition check from devicetree
v5:
  * Declare dependency of a new property
v6:
  * Don't add any new properties, use reset controller only
---
---
 drivers/i2c/muxes/i2c-mux-pca954x.c | 33 +++++++++++++++++++++++------
 1 file changed, 26 insertions(+), 7 deletions(-)

diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
index e09230df7059..eb19a3566d35 100644
--- a/drivers/i2c/muxes/i2c-mux-pca954x.c
+++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
@@ -315,6 +315,26 @@ static u8 pca954x_regval(struct pca954x *data, u8 chan)
 		return 1 << chan;
 }
 
+static void pca954x_reset_assert(struct pca954x *data)
+{
+	if (data->reset_cont)
+		reset_control_assert(data->reset_cont);
+}
+
+static void pca954x_reset_deassert(struct pca954x *data)
+{
+	if (data->reset_cont)
+		reset_control_deassert(data->reset_cont);
+}
+
+static void pca954x_reset_mux(struct pca954x *data)
+{
+	dev_warn(&data->client->dev, "resetting the device\n");
+	pca954x_reset_assert(data);
+	udelay(1);
+	pca954x_reset_deassert(data);
+}
+
 static int pca954x_select_chan(struct i2c_mux_core *muxc, u32 chan)
 {
 	struct pca954x *data = i2c_mux_priv(muxc);
@@ -328,6 +348,8 @@ static int pca954x_select_chan(struct i2c_mux_core *muxc, u32 chan)
 		ret = pca954x_reg_write(muxc->parent, client, regval);
 		data->last_chan = ret < 0 ? 0 : regval;
 	}
+	if (ret == -ETIMEDOUT && (data->reset_cont))
+		pca954x_reset_mux(data);
 
 	return ret;
 }
@@ -337,6 +359,7 @@ static int pca954x_deselect_mux(struct i2c_mux_core *muxc, u32 chan)
 	struct pca954x *data = i2c_mux_priv(muxc);
 	struct i2c_client *client = data->client;
 	s32 idle_state;
+	int ret = 0;
 
 	idle_state = READ_ONCE(data->idle_state);
 	if (idle_state >= 0)
@@ -346,8 +369,10 @@ static int pca954x_deselect_mux(struct i2c_mux_core *muxc, u32 chan)
 	if (idle_state == MUX_IDLE_DISCONNECT) {
 		/* Deselect active channel */
 		data->last_chan = 0;
-		return pca954x_reg_write(muxc->parent, client,
+		ret = pca954x_reg_write(muxc->parent, client,
 					 data->last_chan);
+		if (ret == -ETIMEDOUT && (data->reset_cont))
+			pca954x_reset_mux(data);
 	}
 
 	/* otherwise leave as-is */
@@ -531,12 +556,6 @@ static int pca954x_get_reset(struct device *dev, struct pca954x *data)
 	return 0;
 }
 
-static void pca954x_reset_deassert(struct pca954x *data)
-{
-	if (data->reset_cont)
-		reset_control_deassert(data->reset_cont);
-}
-
 /*
  * I2C init/probing/exit functions
  */
-- 
2.34.1