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NAME
proto — Generic prototyping and diagnostics driver
SYNOPSIS
To compile this driver into the kernel, place the following line in your kernel
configuration file:
device proto
Alternatively, to load the driver as a module at boot time, place the following line in
loader.conf(5):
proto_load="YES"
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:
hw.proto.attach="desc[,desc]"
DESCRIPTION
The proto 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 proto device driver is nothing but a conduit or gateway between user space programs and
the hardware device.
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.
I/O port resources
Device special files created for I/O port resources allow lseek(2), read(2), write(2) and
ioctl(2) operations to be performed on them. The read(2) and 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 proto 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 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 ioctl(2) system
call can be used for the 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:
struct proto_ioc_region {
unsigned long address;
unsigned long size;
};
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 mmap(2).
Reads and writes to the memory address returned by mmap(2) go directly to the hardware. As
such the use of read(2) and 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.
DMA pseudo resource
A device special file named busdma is created for the purpose of doing DMA. It only
supports ioctl(2) and only for the PROTO_IOC_BUSDMA request. This device special file does
not support read(2) nor write(2). The PROTO_IOC_BUSDMA request has an argument that is both
in and out and is defined as follows:
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;
};
The request field is used to specify which DMA operation is to be performed. The 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:
PROTO_IOC_BUSDMA_TAG_CREATE
Create a root tag. The result field is set on output with the key of the DMA tag.
The tag is created with the constraints given by the tag sub-structure. These
constraints correspond roughly to those that can be given to the bus_dma_tag_create(9)
function.
PROTO_IOC_BUSDMA_TAG_DERIVE
Create a derived tag. The 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 result field. The
derived tag combines the constraints of the parent tag with those given by the tag
sub-structure. The combined constraints are written back to the tag sub-structure on
return.
PROTO_IOC_BUSDMA_TAG_DESTROY
Destroy a root or derived tag previously created. The 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.
PROTO_IOC_BUSDMA_MEM_ALLOC
Allocate memory that satisfies the constraints put forth by the tag given in the tag
field of the md sub-structure. The key of the memory descriptor for this memory is
returned in the result field. The 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 virt_addr and virt_size fields. The number of contigous physical
memory segments and the address of the first segment are returned in the phys_nsegs
and 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 bus_nsegs and bus_addr fields. The behaviour of this operation banks
heavily on how bus_dmamem_alloc(9) is implemented, which means that memory is
currently always allocated as a single contigous region of physical memory. In
practice this also tends to give a single contigous region in bus space. This may
change over time.
PROTO_IOC_BUSDMA_MEM_FREE
Free previously allocated memory and destroy the memory desciptor. The proto 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 proto 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.
PROTO_IOC_BUSDMA_MD_CREATE
Create an empty memory descriptor with the tag specified in the tag field of the md
sub-structure. The key of the memory descriptor is returned in the result field.
PROTO_IOC_BUSDMA_MD_DESTROY
Destroy the previously created memory descriptor specified by the key field. When the
memory descriptor is still loaded, it is unloaded first.
PROTO_IOC_BUSDMA_MD_LOAD
Load a contigous region of memory in the memory descriptor specified by the key field.
The size and address in the process' virtual address space are specified by the
virt_size and virt_addr fields. On return, the 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 phys_nsegs and phys_addr fields. The number of bus space
segments and the address of the first segment in bus space is returned in the
bus_nsegs and bus_addr fields.
PROTO_IOC_BUSDMA_MD_UNLOAD
Unload the memory descriptor specified by the key field.
PROTO_IOC_BUSDMA_SYNC
Guarantee that all hardware components have a coherent view of the memory tracked by
the memory descriptor, specified by the 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 base and size fields of the sync sub-structure.
The op field holds the sync operation to be performed. This is similar to the
bus_dmamap_sync(9) function.
PCI configuration space
Access to PCI configuration space is possible through the pcicfg device special file. The
device special file supports lseek(2), read(2) and write(2). Usage is the asme as for I/O
port resources.
FILES
All device special files corresponding to a PCI device are located under
/dev/proto/pci<d>:<b>:<s>:<f> with pci<d>:<b>:<s>:<f> representing the location of the PCI
device in the PCI hierarchy. A PCI location includes:
<d> The PCI domain number
<b> The PCI bus number
<s> The PCI slot or device number
<f> The PCI function number
Every PCI device has a device special file called pcicfg. This device special file gives
access to the PCI configuration space. A device special file called 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 io or mem representing I/O port or memory
mapped I/O space (resp.)
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 /dev/proto/isa:<addr> with 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 io or 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 busdma is created as well. This device special file provides the
interfaces needed for doing DMA.
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.
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:
/dev/proto/pci0:1:2:0/10.mem
/dev/proto/pci0:1:2:0/pcicfg
A legacy floppy controller will have the following device files:
/dev/proto/isa:0x3f0/00.io
/dev/proto/isa:0x3f0/01.io
/dev/proto/isa:0x3f0/busdma
SEE ALSO
ioctl(2), lseek(2), mmap(2), read(2), write(2), bus_dma_tag_create(9), bus_dmamap_sync(9),
bus_dmamem_alloc(9)
AUTHORS
The proto device driver and this manual page were written by Marcel Moolenaar
<marcel@xcllnt.net>.
SECURITY CONSIDERATIONS
Because programs have direct access to the hardware, the proto driver is inherently
insecure. It is not advisable to use this driver on a production machine.
MISSING FUNCTIONALITY
The proto 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.
The proto 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.
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.