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freebsd-skq/share/man/man9/bus_map_resource.9
jhb b4b2ae5652 Add new bus methods for mapping resources. 
Add a pair of bus methods that can be used to "map" resources for direct
CPU access using bus_space(9).  bus_map_resource() creates a mapping and
bus_unmap_resource() releases a previously created mapping.  Mappings are
described by 'struct resource_map' object.  Pointers to these objects can
be passed as the first argument to the bus_space wrapper API used for bus
resources.

Drivers that wish to map all of a resource using default settings
(for example, using uncacheable memory attributes) do not need to change.
However, drivers that wish to use non-default settings can now do so
without jumping through hoops.

First, an RF_UNMAPPED flag is added to request that a resource is not
implicitly mapped with the default settings when it is activated.  This
permits other activation steps (such as enabling I/O or memory decoding
in a device's PCI command register) to be taken without creating a
mapping.  Right now the AGP drivers don't set RF_ACTIVE to avoid using
up a large amount of KVA to map the AGP aperture on 32-bit platforms.
Once RF_UNMAPPED is supported on all platforms that support AGP this
can be changed to using RF_UNMAPPED with RF_ACTIVE instead.

Second, bus_map_resource accepts an optional structure that defines
additional settings for a given mapping.

For example, a driver can now request to map only a subset of a resource
instead of the entire range.  The AGP driver could also use this to only
map the first page of the aperture (IIRC, it calls pmap_mapdev() directly
to map the first page currently).  I will also eventually change the
PCI-PCI bridge driver to request mappings of the subset of the I/O window
resource on its parent side to create mappings for child devices rather
than passing child resources directly up to nexus to be mapped.  This
also permits bridges that do address translation to request suitable
mappings from a resource on the "upper" side of the bus when mapping
resources on the "lower" side of the bus.

Another attribute that can be specified is an alternate memory attribute
for memory-mapped resources.  This can be used to request a
Write-Combining mapping of a PCI BAR in an MI fashion.  (Currently the
drivers that do this call pmap_change_attr() directly for x86 only.)

Note that this commit only adds the MI framework.  Each platform needs
to add support for handling RF_UNMAPPED and thew new
bus_map/unmap_resource methods.  Generally speaking, any drivers that
are calling rman_set_bustag() and rman_set_bushandle() need to be
updated.

Discussed on:	arch
Reviewed by:	cem
Differential Revision:	https://reviews.freebsd.org/D5237
2016-05-20 17:57:47 +00:00

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.\" -*- nroff -*-
.\"
.\" Copyright (c) 2016 John H. Baldwin <jhb@FreeBSD.org>
.\" All rights reserved.
.\"
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.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" $FreeBSD$
.\"
.Dd May 20, 2016
.Dt BUS_MAP_RESOURCE 9
.Os
.Sh NAME
.Nm bus_map_resource , bus_unmap_resource , resource_init_map_request
.Nd map or unmap an active resource
.Sh SYNOPSIS
.In sys/param.h
.In sys/bus.h
.Pp
.In machine/bus.h
.In sys/rman.h
.In machine/resource.h
.Ft int
.Fo bus_map_resource
.Fa "device_t dev" "int type" "struct resource *r"
.Fa "struct resource_map_request *args" "struct resource_map *map"
.Fc
.Ft int
.Fo bus_unmap_resource
.Fa "device_t dev" "int type" "struct resource *r" "struct resource_map *map"
.Fc
.Ft void
.Fn resource_init_map_request "struct resource_map_request *args"
.Sh DESCRIPTION
These functions create or destroy a mapping of a previously activated
resource.
Mappings permit CPU access to the resource via the
.Xr bus_space 9
API.
.Pp
The arguments are as follows:
.Bl -tag -width indent
.It Fa dev
The device that owns the resource.
.It Fa type
The type of resource to map.
It is one of:
.Pp
.Bl -tag -width ".Dv SYS_RES_MEMORY" -compact
.It Dv SYS_RES_IOPORT
for I/O ports
.It Dv SYS_RES_MEMORY
for I/O memory
.El
.It Fa r
A pointer to the
.Vt "struct resource"
returned by
.Xr bus_alloc_resource 9 .
.It Fa args
A set of optional properties to apply when creating a mapping.
This argument can be set to
.Dv NULL
to request a mapping of the entire resource with the default properties.
.It Fa map
The resource mapping to create or destroy.
.El
.Ss Resource Mappings
Resource mappings are described by a
.Vt "struct resource_map"
object.
This structure contains a
.Xr bus_space 9
tag and handle in the
.Va r_bustag
and
.Va r_bushandle
members that can be used for CPU access to the mapping.
The structure also contains a
.Va r_vaddr
member which contains the virtual address of the mapping if one exists.
.Pp
The wrapper API for
.Vt "struct resource"
objects described in
.Xr bus_activate_resource 9
can also be used with
.Vt "struct resource_map" .
For example,
a pointer to a mapping object can be passed as the first argument to
.Fn bus_read_4 .
This wrapper API is preferred over using the
.Va r_bustag
and
.Va r_bushandle
members directly.
.Ss Optional Mapping Properties
The
.Vt "struct resource_map_request"
object passed in
.Fa args
can be used to specify optional properties of a mapping.
The structure must be initialized by invoking
.Fn resource_init_map_request .
Properties are then specified by setting one or more of these members:
.Bl -tag -width indent
.It Va offset , length
These two members specify a region of the resource to map.
By default a mapping is created for the entire resource.
The
.Va offset
is relative to the start of the resource.
.It Va memattr
Specifies a memory attribute to use when mapping the resource.
By default memory mappings use the
.Dv VM_MEMATTR_UNCACHEABLE
attribute.
.El
.Sh EXAMPLES
This maps a PCI memory BAR with the write-combining memory attribute and
reads the first 32-bit word:
.Bd -literal
struct resource *r;
struct resource_map map;
struct resource_map_args args;
uint32_t val;
int rid;
rid = PCIR_BAR(0);
r = bus_alloc_resource_any(dev, SYS_RES_MEMORY, &rid, RF_ACTIVE |
RF_UNMAPPED);
resource_init_map_request(&args);
args.memattr = VM_MEMATTR_WRITE_COMBINING;
bus_map_resource(dev, SYS_RES_MEMORY, r, &args, &map);
val = bus_read_4(&map, 0);
.Ed
.Pp
.Sh RETURN VALUES
Zero is returned on success, otherwise an error is returned.
.Sh SEE ALSO
.Xr bus_activate_resource 9 ,
.Xr bus_alloc_resource 9 ,
.Xr bus_space 9 ,
.Xr device 9 ,
.Xr driver 9
.Sh AUTHORS
This manual page was written by
.An John Baldwin Aq Mt jhb@FreeBSD.org .
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