On 10/09/2020 15.45, James Hilliard wrote:
+static int ftdi_write_eeprom(struct usb_serial_port *port, u8 addr, u16 data)
+{
+ struct usb_device *udev = port->serial->dev;
+ int rv;
+
+ rv = usb_control_msg(udev,
+ usb_sndctrlpipe(udev, 0),
+ FTDI_SIO_WRITE_EEPROM_REQUEST,
+ FTDI_SIO_WRITE_EEPROM_REQUEST_TYPE,
+ data, addr,
+ NULL, 0, WDR_TIMEOUT);
+ if (rv < 0)
+ dev_err(&port->dev, "Unable to write EEPROM: %i\n", rv);
You don't check for a "short write"?
From my understanding the hardware only accepts 2 byte writes, and
the non-counterfeits actually only commit writes on odd addresses
while they buffer writes on even(this difference is what FTDI's windows
driver exploits). So I guess this should be "if (rv < 2)"?
It's not "data" anyway, the data word gets sent in control message
headers. Unless I'm mistaken rv == 0 on success, so the code should be
correct as-is.
+ return rv;
+}
+
+static u16 ftdi_checksum(u16 *data, int n)
+{
+ u16 checksum;
+ int i;
+
+ checksum = 0xaaaa;
+ for (i = 0; i < n - 1; i++) {
+ checksum ^= be16_to_cpu(data[i]);
+ checksum = (checksum << 1) | (checksum >> 15);
+ }
What type of function is this, don't we have all of the needed checksum
functions in the kernel already?
Some custom crc16 style checksum I guess, I'm not seeing anything
in the kernel that's the same, although I might not be looking in the
right places.
This isn't a CRC, it's some random xor all the words thing with a
somewhat pointless rotation in the way. I'd be surprised if anything
elses uses this particular function. Pretty sure other drivers are
littered with stuff like this too, hardware manufacturers love to
reinvent checksums.
--
Hector Martin (hector@xxxxxxxxxxxxxx)
Public Key: https://mrcn.st/pub
