dev-serial: add support for setting data_bits in QEMUSerialSetParams

Also implement the behaviour reported in Linux's ftdi_sio.c whereby if an invalid
data_bits value is provided then the hardware defaults to using 8.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20201027150456.24606-8-mark.cave-ayland@ilande.co.uk
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

hw/usb/dev-serial.c

@@ -308,6 +308,23 @@ static void usb_serial_handle_control(USBDevice *dev, USBPacket *p,
         break;
     }
     case VendorDeviceOutRequest | FTDI_SET_DATA:
+        switch (value & 0xff) {
+        case 7:
+            s->params.data_bits = 7;
+            break;
+        case 8:
+            s->params.data_bits = 8;
+            break;
+        default:
+            /*
+             * According to a comment in Linux's ftdi_sio.c original FTDI
+             * chips fall back to 8 data bits for unsupported data_bits
+             */
+            trace_usb_serial_unsupported_data_bits(bus->busnr, dev->addr,
+                                                   value & 0xff);
+            s->params.data_bits = 8;
+        }
+
         switch (value & FTDI_PARITY) {
         case 0:
             s->params.parity = 'N';

hw/usb/trace-events

@@ -327,6 +327,7 @@ usb_serial_handle_control(int bus, int addr, int request, int value) "dev %d:%u
 usb_serial_unsupported_parity(int bus, int addr, int value) "dev %d:%u unsupported parity %d"
 usb_serial_unsupported_stopbits(int bus, int addr, int value) "dev %d:%u unsupported stop bits %d"
 usb_serial_unsupported_control(int bus, int addr, int request, int value) "dev %d:%u got unsupported/bogus control 0x%x, value 0x%x"
+usb_serial_unsupported_data_bits(int bus, int addr, int value) "dev %d:%u unsupported data bits %d, falling back to 8"
 usb_serial_bad_token(int bus, int addr) "dev %d:%u bad token"
 usb_serial_set_baud(int bus, int addr, int baud) "dev %d:%u baud rate %d"
 usb_serial_set_data(int bus, int addr, int parity, int data, int stop) "dev %d:%u parity %c, data bits %d, stop bits %d"