man/man4/proto.4

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.Dd August 7, 2015
.Dt PROTO 4
.Os
.\"
.Sh NAME
.Nm proto
.Nd Generic prototyping and diagnostics driver
.\"
.Sh SYNOPSIS
To compile this driver into the kernel,
place the following line in your
kernel configuration file:
.Bd -ragged -offset indent
.Cd "device proto"
.Ed
.Pp
Alternatively, to load the driver as a
module at boot time, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
proto_load="YES"
.Ed
.Pp
To have the driver attach to a device instead of its regular driver,
mention it in the list of devices assigned to the following loader variable:
.Bd -ragged -offset indent
hw.proto.attach="desc[,desc]"
.Ed
.\"
.Sh DESCRIPTION
The
.Nm
device driver attaches to PCI or ISA devices when no other device drivers
are present for those devices and it creates device special files for all
resources associated with the device.
The driver itself has no knowledge of the device it attaches to.
Programs can open these device special files and perform register-level
reads and writes.
As such, the
.Nm
device driver is nothing but a conduit or gateway between user space
programs and the hardware device.
.Pp
Examples for why this is useful include hardware diagnostics and prototyping.
In both these use cases, it is far more convenient to develop and run the
logic in user space.
Especially hardware diagnostics requires a somewhat user-friendly interface
and adequate reporting.
Neither is done easily as kernel code.
.Ss I/O port resources
Device special files created for I/O port resources allow
.Xr lseek 2 ,
.Xr read 2 ,
.Xr write 2
and
.Xr ioctl 2
operations to be performed on them.
The
.Xr read 2
and
.Xr write 2
system calls are used to perform input and output (resp.) on the port.
The amount of data that can be read or written at any single time is either
1, 2 or 4 bytes.
While the
.Nm
driver does not prevent reading or writing 8 bytes at a time for some
architectures, it should not be assumed that such actually produces
correct results.
The
.Xr lseek 2
system call is used to select the port number, relative to the I/O port
region being represented by the device special file.
If, for example, the device special file corresponds to an I/O port region
from 0x3f8 to 0x3ff inclusive, then an offset of 4 given to lseek with a
whence value of SEEK_SET will target port 0x3fc on the next read or write
operation.
The
.Xr ioctl 2
system call can be used for the
.Dv PROTO_IOC_REGION
request.
This ioctl request returns the extend of the resource covered by this
device special file.
The extend is returned in the following structure:
.Bd -literal
struct proto_ioc_region {
        unsigned long   address;
        unsigned long   size;
};
.Ed
.Ss Memory mapped I/O resources
The device special files created for memory mapped I/O resources behave
in the same way as those created for I/O port resources.
Additionally, device special files for memory mapped I/O resources allow
the memory to be mapped into the process' address space using
.Xr mmap 2 .
Reads and writes to the memory address returned by
.Xr mmap 2
go directly to the hardware.
As such the use of
.Xr read 2
and
.Xr write 2
can be avoided, reducing the access overhead significantly.
Alignment and access width constraints put forth by the underlying device
apply.
Also, make sure the compiler does not optimize memory accesses away or has
them coalesced into bigger accesses.
.Ss DMA pseudo resource
A device special file named
.Pa busdma
is created for the purpose of doing DMA.
It only supports
.Xr ioctl 2
and only for the
.Dv PROTO_IOC_BUSDMA
request.
This device special file does not support
.Xr read 2
nor
.Xr write 2 .
The
.Dv PROTO_IOC_BUSDMA
request has an argument that is both in and out and is defined as
follows:
.Bd -literal
struct proto_ioc_busdma {
        unsigned int    request;
        unsigned long   key;
        union {
                struct {
                        unsigned long   align;
                        unsigned long   bndry;
                        unsigned long   maxaddr;
                        unsigned long   maxsz;
                        unsigned long   maxsegsz;
                        unsigned int    nsegs;
                        unsigned int    datarate;
                        unsigned int    flags;
                } tag;
                struct {
                        unsigned long   tag;
                        unsigned int    flags;
                        unsigned long   virt_addr;
                        unsigned long   virt_size;
                        unsigned int    phys_nsegs;
                        unsigned long   phys_addr;
                        unsigned long   bus_addr;
                        unsigned int    bus_nsegs;
                } md;
                struct {
                        unsigned int    op;
                        unsigned long   base;
                        unsigned long   size;
                } sync;
        } u;
        unsigned long   result;
};
.Ed
The
.Va request
field is used to specify which DMA operation is to be performed.
The
.Va key
field is used to specify which object the operation applies to.
An object is either a tag or a memory descriptor (md).
The following DMA operations are defined:
.Bl -tag -width XXXX
.It PROTO_IOC_BUSDMA_TAG_CREATE
Create a root tag.
The
.Va result
field is set on output with the key of the DMA tag.
The tag is created with the constraints given by the
.Va tag
sub-structure.
These constraints correspond roughly to those that can be given to the
.Xr bus_dma_tag_create 9
function.
.It PROTO_IOC_BUSDMA_TAG_DERIVE
Create a derived tag.
The
.Va key
field is used to identify the parent tag from which to derive the new tag.
The key of the derived tag is returned in the
.Va result
field.
The derived tag combines the constraints of the parent tag with those
given by the
.Va tag
sub-structure.
The combined constraints are written back to the
.Va tag
sub-structure on return.
.It PROTO_IOC_BUSDMA_TAG_DESTROY
Destroy a root or derived tag previously created.
The
.Va key
field specifies the tag to destroy.
A tag can only be destroyed when not referenced anymore.
This means that derived tags that have this tag as a parent and memory
descriptors created from this tag must be destroyed first.
.It PROTO_IOC_BUSDMA_MEM_ALLOC
Allocate memory that satisfies the constraints put forth by the tag
given in the
.Va tag
field of the
.Va md
sub-structure.
The key of the memory descriptor for this memory is returned in the
.Va result
field.
The
.Va md
sub-structure is filled on return with details of the allocation.
The kernel virtual address and the size of the allocated memory are returned
in the
.Va virt_addr
and
.Va virt_size
fields.
The number of contiguous physical memory segments and the address of the first
segment are returned in the
.Va phys_nsegs
and
.Va phys_addr
fields.
Allocated memory is automatically loaded and thus mapped into bus space.
The number of bus segments and the address of the first segment are returned
in the
.Va bus_nsegs
and
.Va bus_addr
fields.
The behaviour of this operation banks heavily on how
.Xr bus_dmamem_alloc 9
is implemented, which means that memory is currently always allocated as a
single contiguous region of physical memory.
In practice this also tends to give a single contiguous region in bus space.
This may change over time.
.It PROTO_IOC_BUSDMA_MEM_FREE
Free previously allocated memory and destroy the memory descriptor.
The
.Nm
driver is not in a position to track whether the memory has been mapped in
the process' address space, so the application is responsible for unmapping
the memory before it is freed.
The
.Nm
driver also cannot protect against the hardware writing to or reading from
the memory, even after it has been freed.
When the memory is reused for other purposes it can be corrupted or cause
the hardware to behave in unpredictable ways when DMA has not stopped
completely before freeing.
.It PROTO_IOC_BUSDMA_MD_CREATE
Create an empty memory descriptor with the tag specified in the
.Va tag
field of the
.Va md
sub-structure.
The key of the memory descriptor is returned in the
.Va result
field.
.It PROTO_IOC_BUSDMA_MD_DESTROY
Destroy the previously created memory descriptor specified by the
.Va key
field.
When the memory descriptor is still loaded, it is unloaded first.
.It PROTO_IOC_BUSDMA_MD_LOAD
Load a contiguous region of memory in the memory descriptor specified by the
.Va key
field.
The size and address in the process' virtual address space are specified
by the
.Va virt_size
and
.Va virt_addr
fields.
On return, the
.Va md
sub-structure contains the result of the operation.
The number of physical segments and the address of the first segment is
returned in the
.Va phys_nsegs
and
.Va phys_addr
fields.
The number of bus space segments and the address of the first segment in
bus space is returned in the
.Va bus_nsegs
and
.Va bus_addr
fields.
.It PROTO_IOC_BUSDMA_MD_UNLOAD
Unload the memory descriptor specified by the
.Va key
field.
.It PROTO_IOC_BUSDMA_SYNC
Guarantee that all hardware components have a coherent view of the memory
tracked by the memory descriptor, specified by the
.Va key
field.
A sub-section of the memory can be targeted by specifying the relative
offset and size of the memory to make coherent.
The offset and size are given by the
.Va base
and
.Va size
fields of the
.Va sync
sub-structure.
The
.Va op
field holds the sync operation to be performed.
This is similar to the
.Xr bus_dmamap_sync 9
function.
.El
.Ss PCI configuration space
Access to PCI configuration space is possible through the
.Pa pcicfg
device special file.
The device special file supports
.Xr lseek 2 ,
.Xr read 2
and
.Xr write 2 .
Usage is the asme as for I/O port resources.
.Sh FILES
All device special files corresponding to a PCI device are located under
.Pa /dev/proto/pci<d>:<b>:<s>:<f>
with
.Pa pci<d>:<b>:<s>:<f>
representing the location of the PCI device in the PCI hierarchy.
A PCI location includes:
.Pp
.Bl -tag -width XXXXXX -compact -offset indent
.It <d>
The PCI domain number
.It <b>
The PCI bus number
.It <s>
The PCI slot or device number
.It <f>
The PCI function number
.El
.Pp
Every PCI device has a device special file called
.Pa pcicfg .
This device special file gives access to the PCI configuration space.
A device special file called
.Pa busdma
is also created.
This device special file provides the interfaces needed for doing DMA.
For each valid base address register (BAR), a device special file is created
that contains the BAR offset and the resource type.
A resource type can be either
.Pa io
or
.Pa mem
representing I/O port or memory mapped I/O space (resp.)
.Pp
ISA devices do not have a location.
Instead, they are identified by the
first I/O port address or first memory mapped I/O address.
Consequently, all device special files corresponding to an ISA device are
located under
.Pa /dev/proto/isa:<addr>
with
.Pa addr
the address in hexadecimal notation.
For each I/O port or memory mapped I/O address, a device special file is
created that contains the resource identification used by the kernel and
the resource type.
The resource type can be either
.Pa io
or
.Pa mem
representing I/O port or memory mapped I/O space (resp.)
When the device has a DMA channel assigned to it, a device special file
with the name
.Pa busdma
is created as well.
This device special file provides the interfaces needed for doing DMA.
.Pp
If the ISA device is not a Plug-and-Play device nor present in the ACPI
device tree, it must have the appropriate hints so that the kernel can
reserve the resources for it.
.\"
.Sh EXAMPLES
A single function PCI device in domain 0, on bus 1, in slot 2 and having a
single memory mapped I/O region will have the following device special files:
.Pp
.Bl -tag -width XXXXXX -compact -offset indent
.It Pa /dev/proto/pci0:1:2:0/10.mem
.It Pa /dev/proto/pci0:1:2:0/pcicfg
.El
.Pp
A legacy floppy controller will have the following device files:
.Pp
.Bl -tag -width XXXXXX -compact -offset indent
.It Pa /dev/proto/isa:0x3f0/00.io
.It Pa /dev/proto/isa:0x3f0/01.io
.It Pa /dev/proto/isa:0x3f0/busdma
.El
.\"
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr lseek 2 ,
.Xr mmap 2 ,
.Xr read 2 ,
.Xr write 2 ,
.Xr bus_dma_tag_create 9 ,
.Xr bus_dmamap_sync 9 ,
.Xr bus_dmamem_alloc 9
.\"
.Sh AUTHORS
The
.Nm
device driver and this manual page were written by
.An Marcel Moolenaar Aq Mt marcel@xcllnt.net .
.Sh SECURITY CONSIDERATIONS
Because programs have direct access to the hardware, the
.Nm
driver is inherently insecure.
It is not advisable to use this driver on a production machine.
.\"
.Sh MISSING FUNCTIONALITY
The
.Nm
driver does not fully support memory descriptors that need multiple
physical memory segments or multiple bus space segments.
At the very least, an operation is needed on the DMA pseudo resource
for the application to obtain all segments.
.Pp
The
.Nm
driver does not yet support interrupts.
Since interrupts cannot be handled by the driver itself, they must be
converted into signals and delivered to the program that has registered
for interrupts.
A satisfactory mechanism for keeping the interrupt masked during the
signal handling is still being worked out.
.Pp
DMA support for devices other than busmaster devices is not present yet.
The details of how a program is to interact with the DMA controller still
need to be fleshed out.