> -----Original Message----- > From: Laurent Pinchart > > On Monday 04 August 2008, Grant Edwards wrote: > > On 2008-08-04, Laurent Pinchart <laurentp@xxxxxxxxxxxxxxxxx> wrote: (...) > We already have 3 distinct modes for RTS/CTS (see my mail > from today 11:23:36 in this thread). If we add DSR/DTR > hardware support we can easily get 5 or 6 modes. We will run > out of bits in c_cflags. > The three modes which you identify are (A) bus direction (B) send data request (well... RTS=Request To Send :-)) which should be acknowledged by CTS (C) input flow control but, the RTS is widely used for (A)=bus direction BECAUSE it is the same behaviour than (B)=request to send... because RTS was initially made to set the "bus direction" in the attached modem. So the three modes are really 2. People require the (A+B) usage because is in the RS232 and also in V24 specs. But DTR+DSR handshake, really, it's not standardized in any way nor in broad use. I don't think this is a real need (my personal opinion). My company once had a card implementing DTR/DSR flow control, nobody used it and it has been dropped from newer cards. If we really want it we could resort to a setserial flag to say "RTS/CTS flow is implemented with DTR/DSR", but then, why not swapping the pin cabling on the connector then ? My conclusion: only one bit is needed in c_cflags. BUT: think of all the upper APIs (termio, termios, tcset/get... and people using directly TCSET/TCGET ioctls. I am afraid that changing a single bit in such a widely used API might break a lot of existing apps. (...) > > As the number of bits in c_cflags is not infinite we will > need an ioctl to configure the desired hardware handshake > mode (as most modes don't control the data flow I'd rather > talk about hardware handshake which is a more generic name). > We can either use one of the struct serial_struct reserved > fields with TIOCSSERIAL, or create another ioctl. > In the Linux CRIS architecture I've seen an IOCTL doing exactly this, with extra parameters to set the delays RTS-to-Tx and /Tx-to-/RTS. It sounds like a non intrusive way of adding the feature. This would definitely be my preferred way of doing (it's the one which I use in my 16C950 driver). JP Tosoni -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
