Genuine FTDI chips support only CS7/8. A previous fix in commit 8704211f65a2
enforced this limitation and reported it back to userspace.
However, certain types of smartcard readers depend on specific
driver behaviour that requests 0 data bits (not 5) to change into a
different operating mode if CS5 has been set.
This patch reenables this behaviour for all FTDI devices.
Tagged to be added to stable, because it affects a lot of users of
embedded systems which rely on these readers to work properly.
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Heinrich Siebmanns <H.Siebmanns@xxxxxxxxxxx>
Tested-by: Heinrich Siebmanns <H.Siebmanns@xxxxxxxxxxx>
Signed-off-by: Colin Leitner <colin.leitner@xxxxxxxxx>
--
diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index fb0d537..8c204a5 100644
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -2124,10 +2124,20 @@ static void ftdi_set_termios(struct tty_struct *tty,
}
/*
- * All FTDI UART chips are limited to CS7/8. We won't pretend to
+ * All FTDI UART chips are limited to CS7/8. We shouldn't pretend to
* support CS5/6 and revert the CSIZE setting instead.
+ *
+ * CS5 however is used to control some smartcard readers which abuse
+ * this limitation to switch modes. Original FTDI chips fall back to
+ * eight data bits.
+ *
+ * TODO: Implement a quirk to only allow this with mentioned
+ * readers. One I know of (Argolis Smartreader V1)
+ * returns "USB smartcard server" as iInterface string.
+ * The vendor didn't bother with a custom VID/PID of
+ * course.
*/
- if ((C_CSIZE(tty) != CS8) && (C_CSIZE(tty) != CS7)) {
+ if (C_CSIZE(tty) == CS6) {
dev_warn(ddev, "requested CSIZE setting not supported\n");
termios->c_cflag &= ~CSIZE;
@@ -2174,6 +2184,9 @@ no_skip:
urb_value |= FTDI_SIO_SET_DATA_PARITY_NONE;
}
switch (cflag & CSIZE) {
+ case CS5:
+ dev_dbg(ddev, "Setting CS5 quirk\n");
+ break;
case CS7:
urb_value |= 7;
dev_dbg(ddev, "Setting CS7\n");
--
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