--- name: "proto" section: "4freebsd" platform: "linux" package: "freebsd-manpages" version: "12.2-2" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/proto/4freebsd" --- # proto(4freebsd) Generic prototyping and diagnostics driver ## 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)](/loader.conf/5.md): ``` 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)](/lseek/2.md), [read(2)](/read/2.md), [write(2)](/write/2.md) and [ioctl(2)](/ioctl/2.md) operations to be performed on them. The [read(2)](/read/2.md) and [write(2)](/write/2.md) 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)](/lseek/2.md) 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)](/ioctl/2.md) 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)](/mmap/2.md). Reads and writes to the memory address returned by [mmap(2)](/mmap/2.md) go directly to the hardware. As such the use of [read(2)](/read/2.md) and [write(2)](/write/2.md) 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)](/ioctl/2.md) and only for the PROTO\_IOC\_BUSDMA request. This device special file does not support [read(2)](/read/2.md) nor [write(2)](/write/2.md). 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)](/bus_dma_tag_create/9.md) 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)](/bus_dmamem_alloc/9.md) 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)](/bus_dmamap_sync/9.md) function. ### PCI configuration space Access to PCI configuration space is possible through the *pcicfg* device special file. The device special file supports [lseek(2)](/lseek/2.md), [read(2)](/read/2.md) and [write(2)](/write/2.md). 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\:\:\:\* with *pci\:\:\:\* representing the location of the PCI device in the PCI hierarchy. A PCI location includes: - \ The PCI domain number - \ The PCI bus number - \ The PCI slot or device number - \ 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:\* 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)](/ioctl/2.md), [lseek(2)](/lseek/2.md), [mmap(2)](/mmap/2.md), [read(2)](/read/2.md), [write(2)](/write/2.md), [bus\_dma\_tag\_create(9)](/bus_dma_tag_create/9.md), [bus\_dmamap\_sync(9)](/bus_dmamap_sync/9.md), [bus\_dmamem\_alloc(9)](/bus_dmamem_alloc/9.md) ## 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.