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>The Linux 2.4 Parallel Port Subsystem</TH
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NAME="PORTDRIVERS"
></A
>Port drivers</H1
><P
> To recap, then:</P
><P
></P
><UL
COMPACT="COMPACT"
><LI
><P
> The device driver registers itself with <TT
CLASS="LITERAL"
>parport</TT
>.
</P
></LI
><LI
><P
> A low-level driver finds a parallel port and registers it with
<TT
CLASS="LITERAL"
>parport</TT
> (these first two things can happen
in either order). This registration creates a <SPAN
CLASS="STRUCTNAME"
>struct
parport</SPAN
> which is linked onto a list of known ports.
</P
></LI
><LI
><P
> <TT
CLASS="LITERAL"
>parport</TT
> calls the
<TT
CLASS="FUNCTION"
>attach</TT
> function of each registered device
driver, passing it the pointer to the new <SPAN
CLASS="STRUCTNAME"
>struct
parport</SPAN
>.
</P
></LI
><LI
><P
> The device driver gets a handle from
<TT
CLASS="LITERAL"
>parport</TT
>, for use with
<TT
CLASS="FUNCTION"
>parport_claim</TT
>/<TT
CLASS="FUNCTION"
>release</TT
>.
This handle takes the form of a pointer to a <SPAN
CLASS="STRUCTNAME"
>struct
pardevice</SPAN
>, representing a particular device on the
parallel port, and is acquired using
<TT
CLASS="FUNCTION"
>parport_register_device</TT
>.
</P
></LI
><LI
><P
> The device driver claims the port using
<TT
CLASS="FUNCTION"
>parport_claim</TT
> (or
<TT
CLASS="FUNCTION"
>function_claim_or_block</TT
>).
</P
></LI
><LI
><P
> Then it goes ahead and uses the port. When finished it releases
the port.
</P
></LI
></UL
><P
> The purpose of the low-level drivers, then, is to detect parallel
ports and provide methods of accessing them (i.e. implementing the
operations in <SPAN
CLASS="STRUCTNAME"
>struct
parport_operations</SPAN
>).
</P
><P
> A more complete description of which operation is supposed to do
what is available in
<TT
CLASS="FILENAME"
>Documentation/parport-lowlevel.txt</TT
>.
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