.\" .\" Copyright (c) 2014, 2015 Marcel Moolenaar .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. .\" .\" $FreeBSD$ .\" .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 contigous 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 contigous region of physical memory. In practice this also tends to give a single contigous region in bus space. This may change over time. .It PROTO_IOC_BUSDMA_MEM_FREE Free previously allocated memory and destroy the memory desciptor. 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 contigous 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::: with .Pa pci::: representing the location of the PCI device in the PCI hierarchy. A PCI location includes: .Pp .Bl -tag -width XXXXXX -compact -offset indent .It The PCI domain number .It The PCI bus number .It The PCI slot or device number .It 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: 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.