Re: [PATCH 8/9] dev-serial: fix FTDI_GET_MDM_ST response

[Samuel Thibault <samuel.thibault@gnu.org>]

Mark Cave-Ayland, le lun. 26 oct. 2020 10:58:43 +0000, a ecrit:
> On 26/10/2020 09:54, Samuel Thibault wrote:
> > Mark Cave-Ayland, le lun. 26 oct. 2020 08:34:00 +0000, a ecrit:
> > > The FTDI_GET_MDM_ST response should only return a single byte indicating the
> > > modem status with bit 0 cleared (as documented in the Linux ftdi_sio.h header
> > > file).
> > > 
> > > Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
> > > ---
> > >   hw/usb/dev-serial.c | 5 ++---
> > >   1 file changed, 2 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/hw/usb/dev-serial.c b/hw/usb/dev-serial.c
> > > index 4c374d0790..fa734bcf54 100644
> > > --- a/hw/usb/dev-serial.c
> > > +++ b/hw/usb/dev-serial.c
> > > @@ -360,9 +360,8 @@ static void usb_serial_handle_control(USBDevice *dev, USBPacket *p,
> > >           /* TODO: TX ON/OFF */
> > >           break;
> > >       case VendorDeviceRequest | FTDI_GET_MDM_ST:
> > > -        data[0] = usb_get_modem_lines(s) | 1;
> > > -        data[1] = FTDI_THRE | FTDI_TEMT;
> > > -        p->actual_length = 2;
> > > +        data[0] = usb_get_modem_lines(s);
> > > +        p->actual_length = 1;
> > 
[...]
> A quick test shows my Chipi-X returns 0x1 0x60 with nothing attached in
> response to FTDI_SIO_GET_MODEM_STATUS_REQUEST: assuming the reply length
> should be 2 bytes, the comment about B0-B3 being zero and the response from
> my Chip-X above suggests that the "| 1" should still be dropped from the
> response.

Aurelien, you introduced the "| 1" in 

commit abb8a13918ecc1e8160aa78582de9d5224ea70df
Author: Aurelien Jarno <aurelien@aurel32.net>
Date:   Wed Aug 13 04:23:17 2008 +0000

    usb-serial: add support for modem lines

[...]
@@ -357,9 +393,9 @@ static int usb_serial_handle_control(USBDevice *dev, int request, int value,
         /* TODO: TX ON/OFF */
         break;
     case DeviceInVendor | FTDI_GET_MDM_ST:
-        /* TODO: return modem status */
-        data[0] = 0;
-        ret = 1;
+        data[0] = usb_get_modem_lines(s) | 1;
+        data[1] = 0;
+        ret = 2;
         break;

do you know exactly what it is for?

Samuel