Re: [PATCH 2/5] i2c: Add driver for the RTL9300 I2C controller

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Hi Andy,

On 19/09/24 08:27, Andi Shyti wrote:
Hi Chris,

On Wed, Sep 18, 2024 at 11:29:29AM GMT, Chris Packham wrote:
Add support for the I2C controller on the RTL9300 SoC. This is based on
the openwrt implementation[1] but cleaned up to make use of the regmap
APIs.
Can you please add a few more words to describe the device?

Sure will do.

[1] - https://git.openwrt.org/?p=openwrt/openwrt.git;a=blob;f=target/linux/realtek/files-5.15/drivers/i2c/busses/i2c-rtl9300.c

Signed-off-by: Chris Packham <chris.packham@xxxxxxxxxxxxxxxxxxx>
...

+#define I2C_MST_CTRL1		0x0
+#define  MEM_ADDR_OFS		8
+#define  MEM_ADDR_MASK		0xffffff
+#define  SDA_OUT_SEL_OFS	4
+#define  SDA_OUT_SEL_MASK	0x7
+#define  GPIO_SCL_SEL		BIT(3)
+#define  RWOP			BIT(2)
+#define  I2C_FAIL		BIT(1)
+#define  I2C_TRIG		BIT(0)
+#define I2C_MST_CTRL2		0x4
+#define  RD_MODE		BIT(15)
+#define  DEV_ADDR_OFS		8
+#define  DEV_ADDR_MASK		0x7f
+#define  DATA_WIDTH_OFS		4
+#define  DATA_WIDTH_MASK	0xf
+#define  MEM_ADDR_WIDTH_OFS	2
+#define  MEM_ADDR_WIDTH_MASK	0x3
can we have these masked already shifted? You could use
GENMASK().

I'll take a look.

+#define  SCL_FREQ_OFS		0
+#define  SCL_FREQ_MASK		0x3
+#define I2C_MST_DATA_WORD0	0x8
+#define I2C_MST_DATA_WORD1	0xc
+#define I2C_MST_DATA_WORD2	0x10
+#define I2C_MST_DATA_WORD3	0x14
Can we use a prefix for all these defines?

Yes will add "RTL9300_".

I assume for the bit values too? So something like "MEM_ADDR_OFS" becomes "RTL9300_I2C_MST_CTRL1_MEM_ADDR_OFS" is that OK or too verbose?

+
+#define RTL9300_I2C_STD_FREQ		0
+#define RTL9300_I2C_FAST_FREQ		1
This can also be an enum.
Ack

+
+DEFINE_MUTEX(i2c_lock);
...

+static int rtl9300_i2c_write(struct rtl9300_i2c *i2c, u8 *buf, int len)
+{
+	u32 vals[4] = {};
+	int i, ret;
+
+	if (len > 16)
+		return -EIO;
+
+	for (i = 0; i < len; i++) {
+		if (i % 4 == 0)
+			vals[i/4] = 0;
+		vals[i/4] <<= 8;
+		vals[i/4] |= buf[i];
+	}
+
+	ret = regmap_bulk_write(i2c->regmap, i2c->i2c_mst_ofs + I2C_MST_DATA_WORD0,
+				vals, ARRAY_SIZE(vals));
+	if (ret)
+		return ret;
+
+	return len;
why returning "len"? And in any case this is ignored.
I copied that behaviour from the openwrt driver. I think making it the same as the other functions would make more sense.

+}
+
+static int rtl9300_i2c_writel(struct rtl9300_i2c *i2c, u32 data)
+{
+	int ret;
+
+	ret = regmap_write(i2c->regmap, i2c->i2c_mst_ofs + I2C_MST_DATA_WORD0, data);
+	if (ret)
+		return ret;
+
+	return 0;
return regmap_write(...) ?

In any case, the returned value of these functions is completely
ignored, not even printed. Should we either:

  - condier the return value in the _xfer() functions
  or
  - make all these functions void?

I suppose it's a bit academic. Under the hood it's mmio so it's not as if it can really fail (famous last words). That said, this switch chip can be run in a core disabled mode and you could then in theory be doing I2C over SPI from an external SoC. If someone were just naively updating a hardware design to add the external SoC they might neglect to move the I2C connections. It's also just good practice so I'll propagate the returns up to the _xfer().

+}
+
+static int rtl9300_i2c_execute_xfer(struct rtl9300_i2c *i2c, char read_write,
+				int size, union i2c_smbus_data *data, int len)
+{
+	u32 val, mask;
+	int ret;
+
+	if (read_write == I2C_SMBUS_READ)
+		val = 0;
+	else
+		val = RWOP;
+	mask = RWOP;
+
+	val |= I2C_TRIG;
+	mask |= I2C_TRIG;
how about "mask = RWOP | I2C_TRIG" to make it in one line?

Also val can be simplified as:

	val = I2C_TRIG;
	if (read_write == I2C_SMBUS_WRITE)
		val |= RWOP;

Not a binding commeent, as you wish.

I'll take a look. I kind of did like the pairing of val and mask for each thing being set.

+
+	ret = regmap_update_bits(i2c->regmap, i2c->i2c_mst_ofs + I2C_MST_CTRL1, mask, val);
+	if (ret)
+		return ret;
+
+	ret = regmap_read_poll_timeout(i2c->regmap, i2c->i2c_mst_ofs + I2C_MST_CTRL1,
+				       val, !(val & I2C_TRIG), 100, 2000);
+	if (ret)
+		return ret;
+
+	if (val & I2C_FAIL)
where is val taking taking this bit?
In the regmap_read_poll_timeout().

+		return -EIO;
+
...

+	switch (size) {
+	case I2C_SMBUS_QUICK:
...
+	case I2C_SMBUS_BYTE:
...
+	case I2C_SMBUS_BYTE_DATA:
...
+	case I2C_SMBUS_WORD_DATA:
...
+	case I2C_SMBUS_BLOCK_DATA:
...
+	default:
+		dev_warn(&adap->dev, "Unsupported transaction %d\n", size);
dev_err() ?
Ack.
+		ret = -EOPNOTSUPP;
+		goto out_unlock;
+	}
...

+	switch (clock_freq) {
+	case I2C_MAX_STANDARD_MODE_FREQ:
...
+	case I2C_MAX_FAST_MODE_FREQ:
...
+	default:
+		dev_warn(i2c->dev, "clock-frequency %d not supported\n", clock_freq);
+		return -EINVAL;
If we are returning an error we should print an error, let's make
it a "return dev_err_probe()"

But, I was thinking that by default we can assign
I2C_MAX_STANDARD_MODE_FREQ and if the DTS defines a different
frequency we could just print an error and stick to the default
value. Makes sense?

I don't have a strong opinion. Failing the probe just because something in the dts is wrong where we can have a sane default does seem overly harsh. On the other hand I've had hardware QA folks complain when the I2C bus is running at 98khz instead of 100khz.


+	}
...

+	return i2c_add_adapter(adap);
return devm_i2c_add_adapter(adap);

and the remove function is not needed.

OK thanks. I did look for a devm variant but obviously not hard enough.

+}
+
+static void rtl9300_i2c_remove(struct platform_device *pdev)
+{
+	struct rtl9300_i2c *i2c = platform_get_drvdata(pdev);
+
+	i2c_del_adapter(&i2c->adap);
+}
+
+static const struct of_device_id i2c_rtl9300_dt_ids[] = {
+	{ .compatible = "realtek,rtl9300-i2c" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, i2c_rtl9300_dt_ids);
+
+static struct platform_driver rtl9300_i2c_driver = {
+	.probe = rtl9300_i2c_probe,
+	.remove = rtl9300_i2c_remove,
+	.driver = {
+		.name = "i2c-rtl9300",
+		.of_match_table = i2c_rtl9300_dt_ids,
+	},
+};
+
+module_platform_driver(rtl9300_i2c_driver);
+
+MODULE_DESCRIPTION("RTL9300 I2C controller driver");
+MODULE_LICENSE("GPL");
+
Just a trailing blank line here.
Ack.

Thanks,
Andi






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