Re: [PATCH v2 25/31] i2c: fsi: Calculate clock divider from local bus frequency

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On 4/16/24 16:20, Guenter Roeck wrote:
On Tue, Apr 16, 2024 at 01:09:04PM -0500, Eddie James wrote:
On 4/15/24 17:11, Andi Shyti wrote:
Hi Eddie,

@@ -689,6 +692,20 @@ static int fsi_i2c_probe(struct device *dev)
   	mutex_init(&i2c->lock);
   	i2c->fsi = to_fsi_dev(dev);
   	INIT_LIST_HEAD(&i2c->ports);
+	i2c->clock_div = I2C_DEFAULT_CLK_DIV;
+
+	lbus = fsi_device_local_bus_frequency(i2c->fsi);
+	if (lbus) {
+		u32 clock = I2C_DEFAULT_CLK_RATE;
I don't see the need for initialization.

Does device_property_read_u32 set clock if the property isn't found? If not,
it needs to be initialized here. Or I can set it in an else statement from
device_property_read_u32.


+
+		if (!device_property_read_u32(dev, "clock-frequency", &clock)) {
+			if (!clock)
+				clock = I2C_DEFAULT_CLK_RATE;
+		}
		if (device_property_read_u32(dev, "clock-frequency", &clock) || !clock)
			clock = I2C_DEFAULT_CLK_RATE;


Nice one, thanks.



+
+		// i2c clock rate = local bus clock / (4 * (i2c clock div + 1))
You forgot to remove this.

I actually meant to leave that comment to explain how the clock rate is
calculated, as the reverse calculation in the code is a little more
confusing.

Partially that is because you implemented DIV_ROUND_UP() manually.


Thanks Guenter, good point.


Eddie


Andi

+		i2c->clock_div = (((lbus + (clock - 1)) / clock) / 4) - 1;
				= DIV_ROUND_UP(lbus, clock) / 4 - 1

Guenter




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