Hello Ed !
Thanks for the feedback. 

Please read my coments (doubts actually) below:

quoted

4 - INPCK flag: What's the purpose of this flag. What's the 
diference in 
relation to IGNPAR;

     If INPCK is set, input parity checking  is  enabled.      If
     INPCK is  not  set, input parity checking is disabled.  This
     allows output parity generation without input parity errors.
     Note  that  whether input parity checking is enabled or dis-
     abled is independent of whether parity detection is  enabled
     or disabled. If parity detection is enabled but input parity
     checking is disabled, the hardware to which the terminal  is
     connected  will  recognize  the parity bit, but the terminal
     special file will not check whether this is set correctly or
     not.

     If IGNPAR is set, a  byte  with  framing  or  parity  errors
     (other than break) is ignored. This means that the data byte
     with the error is thrown away  by the  driver as if the byte
     had never been received. 

In short,
If INPCK is _not_ set, then all received data bytes will be delivered 
to the user level, regardless of parity errors.
If IGNPAR is set, then only received data bytes that do not have 
parity errors will be delivered to the user level.
If PARENB is _not_ set, then the receiver hardware will not detect 
bad parity, so all received data bytes are considered free of errors. 
Since there are no data bytes with associated error indications, 
setting IGNPAR would have no effect. All of the data are considered 
error free.

Your explanation makes sense to me. With this information I built the
table:
   IGNPAR    INPCK         ACTION:
     0         0           Deliver all data to the user-level
     0         1           Check parity. Discard erroneous bytes
     1         0           ????
     1         1           Check parity. Discard erroneous bytes 

What goes on ????   ?

quoted

5 - If the TTY knows the data status (PARITY, FRAMING, 
OVERRUN, NORMAL), 
why the driver has to deal with the flag IGNPAR. Shouldn't 
the TTY being 
doing it ?

Not sure I understand the question. Received data does not carry any
information about errors with it after it leaves the driver, unless 
PARMRK is set. 

When the driver copy the data from the controler to the flip buffer it
copies the data to the buffer tty->flip.char_buf_ptr and it set a flag
(TTY_NORMAL, TTY_PARITY, TTY_FRAME, etc) on the buffer
tty->flip.flag_buf_ptr telling the TTY how this byte was received. So
the TTY knows if certain byte was problematic or not. Did you understand
my doubt know ?

Thanks for your patience
Henrique