Re: [PATCH 2/2] usb: misc: usb5744: Add support for USB hub controller

Hi Andrew,

On 2/10/21 3:52 AM, Andrew Lunn wrote:

On Tue, Feb 09, 2021 at 10:53:20AM +0100, Michal Simek wrote:

quoted

+static int usb5744_i2c_probe(struct i2c_client *client,
+			     const struct i2c_device_id *id)
+{
+	struct device *dev = &client->dev;
+	int ret;
+
+	/* Trigger gpio reset to the hub. */
+	ret = usb5744_init_hw(dev);
+	if (ret)
+		return ret;
+
+	/* Send SMBus command to boot hub. */
+	ret = i2c_smbus_write_word_data(client, 0xAA, swab16(0x5600));

Hi Michal

This is not my area of the kernel. But that swab16() stood out, and
made me wonder about endianness. Will this work correctly on big and
little endian hosts?

thanks for bringing this up. I didn't test it on BE system.

I have grepped the kernel

[linux](xnext/usb5744)$ git grep i2c_smbus_write_word_data | grep swab
drivers/media/i2c/uda1342.c:17:	i2c_smbus_write_word_data(client, reg,
swab16(value));
drivers/media/i2c/vpx3220.c:97:	if (i2c_smbus_write_word_data(client,
0x27, swab16(fpaddr)) == -1) {
drivers/media/i2c/vpx3220.c:106:	if (i2c_smbus_write_word_data(client,
0x28, swab16(data)) == -1) {
drivers/media/i2c/vpx3220.c:120:	if (i2c_smbus_write_word_data(client,
0x26, swab16(fpaddr)) == -1) {
drivers/usb/misc/usb5744.c:50:	ret = i2c_smbus_write_word_data(client,
0xAA, swab16(0x5600));
include/linux/i2c.h:168:	return i2c_smbus_write_word_data(client,
command, swab16(value));

And last one is interesting

 164 static inline s32
 165 i2c_smbus_write_word_swapped(const struct i2c_client *client,
 166                              u8 command, u16 value)
 167 {
 168         return i2c_smbus_write_word_data(client, command,
swab16(value));
 169 }

And this function is also used

[linux](xnext/usb5744)$ git grep i2c_smbus_write_word_swapped | wc -l
76

I think it would be the best to test it and see if this code works on BE
but I need to prepare it first.
And current code is aligned with others but it doesn't mean that it is
correct.

Thanks,
Michal