https://bugzilla.kernel.org/show_bug.cgi?id=210351 --- Comment #2 from Vladimir (svv75@xxxxxxx) --- Hello, Johan. Unfortunately, I don't have a device at hand right now. But I remember the lsusb output was showing FT-X type. And under Windows, all three chips I mentioned work correctly with all prescalers. I contacted FTDI tech support with this problem. They advised me to have such a patch for ftdi_sio.c and it solved the problem. Here's the patch: static int change_speed (struct tty_struct * tty, struct usb_serial_port * port) ... index_value = get_ftdi_divisor (tty, port); value = (u16) index_value; index = (u16) (index_value >> 16); if ((priv-> chip_type == FT2232C) || (priv-> chip_type == FT2232H) || (priv-> chip_type == FT4232H) || (priv-> chip_type == FT232H)) { / * Probably the BM type needs the MSB of the encoded fractional * divider also moved like for the chips above. Any infos? * / index = (u16) ((index << 8) | priv-> interface); } So, the high bit of the factional part is lost on the FT-X chips. To fix it in the kernel try: if ((priv-> chip_type == FT2232C) || (priv-> chip_type == FT2232H) || (priv-> chip_type == FT4232H) || (priv-> chip_type == FT232H) || (priv-> chip_type == FTX)) { / * Probably the BM type needs the MSB of the encoded fractional * divider also moved like for the chips above. Any infos? * / index = (u16) ((index << 8) | priv-> interface); } But I don't know why the most significant bit of the prescaler is masked by something. I have no information about the chip configuration registers. It looks like this is confidential information. But they could provide it to you as the driver developer. Vladimir -- You may reply to this email to add a comment. You are receiving this mail because: You are watching the assignee of the bug.
