[PATCH] crypto: atmel-i2c - find the bus speed behind an I2C mux

[PATCH] crypto: atmel-i2c - find the bus speed behind an I2C mux

[Josef Schlehofer]

On the Turris Omnia, the ATSHA204A sits behind a PCA9547 I2C mux. The
driver reads "clock-frequency" from the mux channel, which has no such
property, so the probe fails with -EINVAL:

  atmel-sha204a 6-0064: failed to read clock-frequency property

A device tree patch in 2024 added the property to the mux channel. The
review rejected it, because the I2C core ignores the property there. The
driver would then compute the wake token for a wrong bus speed. The
review asked for a fix in the driver, but none was sent.

Keep reading the property of the client's adapter first, as before. If
it has none, look at the parent adapters. If no adapter has it, use
100 kHz, the default of most I2C controller drivers.

Fixes: 11105693fa05 ("crypto: atmel-ecc - introduce Microchip / Atmel ECC driver")
Cc: stable@vger.kernel.org # v5.19+
Reported-by: Marius Dinu <m95d@psihoexpert.ro>
Closes: https://lore.kernel.org/all/46ea55652f8bcdef51d5c552902fd0cc@psihoexpert.ro/
Link: https://lore.kernel.org/all/20240515104149.2ce3566e@dellmb/
Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>
---
Tested on a Turris Omnia with 7.2.13 and 6.18.59: the driver probes, and
/dev/hwrng reads random data from the ATSHA204A. The mv64xxx controller
stops at the address NAK, so this test does not exercise the token size.

 drivers/crypto/atmel-i2c.c | 29 ++++++++++++++++++++---------
 1 file changed, 20 insertions(+), 9 deletions(-)

diff --git a/drivers/crypto/atmel-i2c.c b/drivers/crypto/atmel-i2c.c
index 24bded4..5ff7bf5 100644
--- a/drivers/crypto/atmel-i2c.c
+++ b/drivers/crypto/atmel-i2c.c
@@ -347,11 +347,28 @@ free_cmd:
 	return ret;
 }
 
+/*
+ * A device behind an I2C mux sits on a channel adapter. Try the adapter of
+ * the client first, as before, then its parents. Without the property,
+ * assume 100 kHz, the default of most I2C controller drivers.
+ */
+static u32 atmel_i2c_bus_speed(struct i2c_adapter *adap)
+{
+	u32 bus_clk_rate;
+
+	for (; adap; adap = i2c_parent_is_i2c_adapter(adap)) {
+		if (!device_property_read_u32(&adap->dev, "clock-frequency",
+					      &bus_clk_rate) && bus_clk_rate)
+			return bus_clk_rate;
+	}
+
+	return I2C_MAX_STANDARD_MODE_FREQ;
+}
+
 int atmel_i2c_probe(struct i2c_client *client)
 {
 	struct atmel_i2c_client_priv *i2c_priv;
 	struct device *dev = &client->dev;
-	int ret;
 	u32 bus_clk_rate;
 
 	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
@@ -360,14 +377,8 @@ int atmel_i2c_probe(struct i2c_client *client)
 	}
 
 	bus_clk_rate = i2c_acpi_find_bus_speed(&client->adapter->dev);
-	if (!bus_clk_rate) {
-		ret = device_property_read_u32(&client->adapter->dev,
-					       "clock-frequency", &bus_clk_rate);
-		if (ret) {
-			dev_err(dev, "failed to read clock-frequency property\n");
-			return ret;
-		}
-	}
+	if (!bus_clk_rate)
+		bus_clk_rate = atmel_i2c_bus_speed(client->adapter);
 
 	if (bus_clk_rate > I2C_MAX_FAST_MODE_PLUS_FREQ) {
 		dev_err(dev, "%u exceeds maximum supported clock frequency (1MHz)\n",
-- 
2.54.0 (Apple Git-157)