Document ioctl(2) operations of the agp(4) subsystem. The original patch

was obtained from [1], with heavy editing, and ammending text for some of
the ioctls.

All ioctls (in sys/agpio.h) are now documented.

PR: docs/50503
Original patch by: Alex Semenyaka <alexs@snark.ratmir.ru> [1]

Content approved by:

	- Eric Anholt <anholt@FreeBSD.ORG>
	- Matthew N. Dodd <mdodd@FreeBSD.ORG> (cursory review)

Approved and Reviewed by: des (mentor), re (scottl)

share/man/man4/agp.4

@@ -58,6 +58,105 @@ The most common application of
 is for running
 .Xr XFree86 1
 on the Intel i81x controllers.
+.Sh IOCTLS
+The following
+.Xr ioctl 2
+operations can be performed on
+.Pa /dev/agpgart ,
+which are defined in
+.Aq Pa sys/agpio.h :
+.Ss Dv AGPIOC_INFO
+Returns state of the
+.Nm
+system.
+The result is a pointer to the following structure:
+.Bd -literal
+typedef struct _agp_info {
+	agp_version version;  /* version of the driver        */
+	u_int32_t bridge_id;  /* bridge vendor/device         */
+	u_int32_t agp_mode;   /* mode info of bridge          */
+	off_t aper_base;      /* base of aperture             */
+	size_t aper_size;     /* size of aperture             */
+	size_t pg_total;      /* max pages (swap + system)    */
+	size_t pg_system;     /* max pages (system)           */
+	size_t pg_used;       /* current pages used           */
+} agp_info;
+.Ed
+.Ss Dv AGPIOC_ACQUIRE
+Acquire control of the AGP chipset for use by this client.
+Returns
+.Er EBUSY
+if the AGP chipset is already acquired by another client.
+.Ss Dv AGPIOC_RELEASE
+Release control of the AGP chipset.
+This does not unbind or free any allocated memory, which is the
+responsibility of the client to handle if necessary.
+.Ss Dv AGPIOC_SETUP
+Enable the AGP hardware with the relevant mode.
+This
+.Xr ioctl 2
+takes the following structure:
+.Bd -literal
+typedef struct _agp_setup {
+	u_int32_t agp_mode;   /* mode info of bridge */
+} agp_setup;
+.Ed
+.Pp
+The mode bits are defined in
+.Aq Pa sys/agpio.h .
+.Ss Dv AGPIOC_ALLOCATE
+Allocate physical memory suitable for mapping into the AGP aperture.
+This
+.Xr ioctl 2
+takes the following structure:
+.Bd -literal
+typedef struct _agp_allocate {
+	int key;              /* tag of allocation            */
+	size_t pg_count;      /* number of pages              */
+	u_int32_t type;       /* 0 == normal, other devspec   */
+	u_int32_t physical;   /* device specific (some devices  
+			       * need a phys address of the     
+			       * actual page behind the gatt
+			       * table)                       */
+} agp_allocate;
+.Ed
+.Pp
+Returns a handle to the allocated memory.
+.Ss Dv AGPIOC_DEALLOCATE
+Free the previously allocated memory associated with the handle passed.
+.Ss Dv AGPIOC_BIND
+Bind the allocated memory at given offset with the AGP aperture.
+Returns
+.Er EINVAL
+if the memory is already bound or the offset is not at AGP page boundary.
+This
+.Xr ioctl 2
+takes the following structure:
+.Bd -literal
+typedef struct _agp_bind {
+	int key;         /* tag of allocation            */
+	off_t pg_start;  /* starting page to populate    */
+} agp_bind;
+.Ed
+.Pp
+The
+.Sq tag of allocation ,
+is the handle returned by
+.Dv AGPIOC_ALLOCATE.
+.Ss Dv AGPIOC_UNBIND
+Unbind memory from the AGP aperture.
+Returns
+.Er EINVAL
+if the memory is not bound.
+This
+.Xr ioctl
+takes the following structure:
+.Bd -literal
+typedef struct _agp_unbind {
+	int key;                /* tag of allocation         */
+	u_int32_t priority;     /* priority for paging out   */
+} agp_unbind;
+.Ed
 .Sh FILES
 .Bl -tag -width ".Pa /dev/agpgart" -compact
 .It Pa /dev/agpgart