On Tue, Feb 28, 2017 at 12:51:24PM +0000, Ian Abbott wrote:
> If a BM type chip has iSerialNumber set to 0 in its EEPROM, an incorrect
> value is read from the bcdDevice field of the USB descriptor, making it
> look like an AM type chip. Attempt to correct this in
> ftdi_determine_type() by attempting to read the latency timer for an AM
> type chip. If that succeeds, assume it is a BM type chip.
>
> Currently, read_latency_timer() bails out without reading the latency
> timer for an AM type chip, so factor out the guts of
> read_latency_timer() into a new function _read_latency_timer() that
> attempts to read the latency timer regardless of chip type, and returns
> either the latency timer value or a negative error number.
>
> Signed-off-by: Ian Abbott <abbo...@mev.co.uk>
> ---
> drivers/usb/serial/ftdi_sio.c | 38 ++++++++++++++++++++++++++++++--------
> 1 file changed, 30 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
> index 72314734dfd0..a1b90f4184a7 100644
> --- a/drivers/usb/serial/ftdi_sio.c
> +++ b/drivers/usb/serial/ftdi_sio.c
> @@ -1609,9 +1623,17 @@ static void ftdi_determine_type(struct usb_serial_port
> *port)
> priv->baud_base = 12000000 / 16;
> } else if (version < 0x400) {
> /* Assume it's an FT8U232AM (or FT8U245AM) */
> - /* (It might be a BM because of the iSerialNumber bug,
> - * but it will still work as an AM device.) */
> priv->chip_type = FT8U232AM;
> + /*
> + * It might be a BM type because of the iSerialNumber bug.
> + * If the latency timer is readable, assume it is BM type.
> + */
> + if (_read_latency_timer(port) >= 0) {
Would it be possible to only try to read the latency timer when
iSerialNumber is 0?
> + dev_dbg(&port->dev,
> + "%s: has latency timer so not an AM type\n",
> + __func__);
> + priv->chip_type = FT232BM;
> + }
> } else if (version < 0x600) {
> /* Assume it's an FT232BM (or FT245BM) */
> priv->chip_type = FT232BM;
Thanks,
Johan
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