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 it has iSerialNumber set to 0. 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 <abbotti@xxxxxxxxx>
---
v2:
- As suggested by Johan Hovold, only attempt to read latency timer for
AM type chip if iSerialNumber is 0 (indicating that it might be a BM
type chip with iSerialNumber bug).
---
drivers/usb/serial/ftdi_sio.c | 40 ++++++++++++++++++++++++++++++++--------
1 file changed, 32 insertions(+), 8 deletions(-)
diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index 72314734dfd0..be2c77380320 100644
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -1425,16 +1425,13 @@ static int write_latency_timer(struct usb_serial_port *port)
return rv;
}
-static int read_latency_timer(struct usb_serial_port *port)
+static int _read_latency_timer(struct usb_serial_port *port)
{
struct ftdi_private *priv = usb_get_serial_port_data(port);
struct usb_device *udev = port->serial->dev;
unsigned char *buf;
int rv;
- if (priv->chip_type == SIO || priv->chip_type == FT8U232AM)
- return -EINVAL;
-
buf = kmalloc(1, GFP_KERNEL);
if (!buf)
return -ENOMEM;
@@ -1446,11 +1443,10 @@ static int read_latency_timer(struct usb_serial_port *port)
0, priv->interface,
buf, 1, WDR_TIMEOUT);
if (rv < 1) {
- dev_err(&port->dev, "Unable to read latency timer: %i\n", rv);
if (rv >= 0)
rv = -EIO;
} else {
- priv->latency = buf[0];
+ rv = buf[0];
}
kfree(buf);
@@ -1458,6 +1454,24 @@ static int read_latency_timer(struct usb_serial_port *port)
return rv;
}
+static int read_latency_timer(struct usb_serial_port *port)
+{
+ struct ftdi_private *priv = usb_get_serial_port_data(port);
+ int rv;
+
+ if (priv->chip_type == SIO || priv->chip_type == FT8U232AM)
+ return -EINVAL;
+
+ rv = _read_latency_timer(port);
+ if (rv < 0) {
+ dev_err(&port->dev, "Unable to read latency timer: %i\n", rv);
+ return rv;
+ }
+
+ priv->latency = rv;
+ return 0;
+}
+
static int get_serial_info(struct usb_serial_port *port,
struct serial_struct __user *retinfo)
{
@@ -1609,9 +1623,19 @@ 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 iSerialNumber==0 and the latency timer is readable,
+ * assume it is BM type.
+ */
+ if (udev->descriptor.iSerialNumber == 0 &&
+ _read_latency_timer(port) >= 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;
--
2.11.0
--
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