[Linux-parport] What is the purpose of PARPORT_MODE_PCSPP?

[Alex Henrie]

Dear kernel developers,

I've been looking at the Linux parport API and I have a question: What
is the purpose of PARPORT_MODE_PCSPP? According to the
documentation,[1] that flag means:

> IBM PC registers are available,
> i.e. functions that act on data,
> control and status registers are
> probably writing directly to the
> hardware.

That makes it sound like the flag indicates whether base (and base_hi
if ECP) in struct parport are valid. A flag like that would make sense
to me because base=0 might be valid on some architecture, and on top
of that, device drivers might need to account for extra latency from
indirect I/O. But, as far as I can tell, every parport driver just
sets the flag regardless of whether it writes directly to registers or
whether it sends writes over the USB bus, and a flag that is always on
doesn't mean much.

Phrased another way: Should PARPORT_MODE_PCSPP be removed from the
uss720 and mos7720 drivers, or am I just misunderstanding the purpose
of the flag?

-Alex

[1] https://docs.kernel.org/driver-api/parport-lowlevel.html