This chapter will talk about the FreeBSD mechanisms for writing a device driver for a device on a PCI bus. Information here about how the PCI bus code iterates through the unattached devices and see if a newly loaded kld will attach to any of them. /* * Simple KLD to play with the PCI functions. * * Murray Stokely */ #define MIN(a,b) (((a) < (b)) ? (a) : (b)) #include <sys/param.h> /* defines used in kernel.h */ #include <sys/module.h> #include <sys/systm.h> #include <sys/errno.h> #include <sys/kernel.h> /* types used in module initialization */ #include <sys/conf.h> /* cdevsw struct */ #include <sys/uio.h> /* uio struct */ #include <sys/malloc.h> #include <sys/bus.h> /* structs, prototypes for pci bus stuff */ #include <machine/bus.h> #include <sys/rman.h> #include <machine/resource.h> #include <dev/pci/pcivar.h> /* For get_pci macros! */ #include <dev/pci/pcireg.h> /* Function prototypes */ d_open_t mypci_open; d_close_t mypci_close; d_read_t mypci_read; d_write_t mypci_write; /* Character device entry points */ static struct cdevsw mypci_cdevsw = { .d_open = mypci_open, .d_close = mypci_close, .d_read = mypci_read, .d_write = mypci_write, .d_name = "mypci", }; /* vars */ static dev_t sdev; /* We're more interested in probe/attach than with open/close/read/write at this point */ int mypci_open(dev_t dev, int oflags, int devtype, d_thread_t *td) { int err = 0; printf("Opened device \"mypci\" successfully.\n"); return (err); } int mypci_close(dev_t dev, int fflag, int devtype, d_thread_t *td) { int err = 0; printf("Closing device \"mypci.\"\n"); return (err); } int mypci_read(dev_t dev, struct uio *uio, int ioflag) { int err = 0; printf("mypci read!\n"); return (err); } int mypci_write(dev_t dev, struct uio *uio, int ioflag) { int err = 0; printf("mypci write!\n"); return (err); } /* PCI Support Functions */ /* * Return identification string if this is device is ours. */ static int mypci_probe(device_t dev) { device_printf(dev, "MyPCI Probe\nVendor ID : 0x%x\nDevice ID : 0x%x\n", pci_get_vendor(dev), pci_get_device(dev)); if (pci_get_vendor(dev) == 0x11c1) { printf("We've got the Winmodem, probe successful!\n"); return (0); } return (ENXIO); } /* Attach function is only called if the probe is successful */ static int mypci_attach(device_t dev) { printf("MyPCI Attach for : deviceID : 0x%x\n",pci_get_vendor(dev)); sdev = make_dev(&mypci_cdevsw, 0, UID_ROOT, GID_WHEEL, 0600, "mypci"); printf("Mypci device loaded.\n"); return (ENXIO); } /* Detach device. */ static int mypci_detach(device_t dev) { printf("Mypci detach!\n"); return (0); } /* Called during system shutdown after sync. */ static int mypci_shutdown(device_t dev) { printf("Mypci shutdown!\n"); return (0); } /* * Device suspend routine. */ static int mypci_suspend(device_t dev) { printf("Mypci suspend!\n"); return (0); } /* * Device resume routine. */ static int mypci_resume(device_t dev) { printf("Mypci resume!\n"); return (0); } static device_method_t mypci_methods[] = { /* Device interface */ DEVMETHOD(device_probe, mypci_probe), DEVMETHOD(device_attach, mypci_attach), DEVMETHOD(device_detach, mypci_detach), DEVMETHOD(device_shutdown, mypci_shutdown), DEVMETHOD(device_suspend, mypci_suspend), DEVMETHOD(device_resume, mypci_resume), { 0, 0 } }; static driver_t mypci_driver = { "mypci", mypci_methods, 0, /* sizeof(struct mypci_softc), */ }; static devclass_t mypci_devclass; DRIVER_MODULE(mypci, pci, mypci_driver, mypci_devclass, 0, 0); Additional Resources PCI Special Interest Group PCI System Architecture, Fourth Edition by Tom Shanley, et al. FreeBSD provides an object-oriented mechanism for requesting resources from a parent bus. Almost all devices will be a child member of some sort of bus (PCI, ISA, USB, SCSI, etc) and these devices need to acquire resources from their parent bus (such as memory segments, interrupt lines, or DMA channels). To do anything particularly useful with a PCI device you will need to obtain the Base Address Registers (BARs) from the PCI Configuration space. The PCI-specific details of obtaining the BAR are abstracted in the bus_alloc_resource() function. For example, a typical driver might have something similar to this in the attach() function: sc->bar0id = PCIR_BAR(0); sc->bar0res = bus_alloc_resource(dev, SYS_RES_MEMORY, &(sc->bar0id), 0, ~0, 1, RF_ACTIVE); if (sc->bar0res == NULL) { printf("Memory allocation of PCI base register 0 failed!\n"); error = ENXIO; goto fail1; } sc->bar1id = PCIR_BAR(1); sc->bar1res = bus_alloc_resource(dev, SYS_RES_MEMORY, &(sc->bar1id), 0, ~0, 1, RF_ACTIVE); if (sc->bar1res == NULL) { printf("Memory allocation of PCI base register 1 failed!\n"); error = ENXIO; goto fail2; } sc->bar0_bt = rman_get_bustag(sc->bar0res); sc->bar0_bh = rman_get_bushandle(sc->bar0res); sc->bar1_bt = rman_get_bustag(sc->bar1res); sc->bar1_bh = rman_get_bushandle(sc->bar1res); Handles for each base address register are kept in the softc structure so that they can be used to write to the device later. These handles can then be used to read or write from the device registers with the bus_space_* functions. For example, a driver might contain a shorthand function to read from a board specific register like this: uint16_t board_read(struct ni_softc *sc, uint16_t address) { return bus_space_read_2(sc->bar1_bt, sc->bar1_bh, address); } Similarly, one could write to the registers with: void board_write(struct ni_softc *sc, uint16_t address, uint16_t value) { bus_space_write_2(sc->bar1_bt, sc->bar1_bh, address, value); } These functions exist in 8bit, 16bit, and 32bit versions and you should use bus_space_{read|write}_{1|2|4} accordingly. Interrupts are allocated from the object-oriented bus code in a way similar to the memory resources. First an IRQ resource must be allocated from the parent bus, and then the interrupt handler must be set up to deal with this IRQ. Again, a sample from a device attach() function says more than words. /* Get the IRQ resource */ sc->irqid = 0x0; sc->irqres = bus_alloc_resource(dev, SYS_RES_IRQ, &(sc->irqid), 0, ~0, 1, RF_SHAREABLE | RF_ACTIVE); if (sc->irqres == NULL) { printf("IRQ allocation failed!\n"); error = ENXIO; goto fail3; } /* Now we should set up the interrupt handler */ error = bus_setup_intr(dev, sc->irqres, INTR_TYPE_MISC, my_handler, sc, &(sc->handler)); if (error) { printf("Couldn't set up irq\n"); goto fail4; } sc->irq_bt = rman_get_bustag(sc->irqres); sc->irq_bh = rman_get_bushandle(sc->irqres); Some care must be taken in the detach routine of the driver. You must quiesce the device's interrupt stream, and remove the interrupt handler. Once bus_teardown_intr() has returned, you know that your interrupt handler will no longer be called and that all threads that might have been executing this interrupt handler have returned. Since this function can sleep, you must not hold any mutexes when calling this function. This section is obsolete, and present only for historical reasons. The proper methods for dealing with these issues is to use the bus_space_dma*() functions instead. This paragraph can be removed when this section is updated to reflect that usage. However, at the moment, the API is in a bit of flux, so once that settles down, it would be good to update this section to reflect that. On the PC, peripherals that want to do bus-mastering DMA must deal with physical addresses. This is a problem since FreeBSD uses virtual memory and deals almost exclusively with virtual addresses. Fortunately, there is a function, vtophys() to help. #include <vm/vm.h> #include <vm/pmap.h> #define vtophys(virtual_address) (...) The solution is a bit different on the alpha however, and what we really want is a function called vtobus(). #if defined(__alpha__) #define vtobus(va) alpha_XXX_dmamap((vm_offset_t)va) #else #define vtobus(va) vtophys(va) #endif It is very important to deallocate all of the resources that were allocated during attach(). Care must be taken to deallocate the correct stuff even on a failure condition so that the system will remain usable while your driver dies.