PCI设备驱动解析

首先我想引用一下官方的源代码中的文档，对设备驱动的工作做一个概括性的叙述：

1 首先是调用 pci_register_driver()函数，对设备进行注册。 2.Once the driver knows about a PCI device and takes ownership, the driver generally needs to perform the following initialization: Enable the device Request MMIO/IOP resources Set the DMA mask size (for both coherent and streaming DMA) Allocate and initialize shared control data (pci_allocate_coherent()) Access device configuration space (if needed) Register IRQ handler (request_irq()) Initialize non-PCI (i.e. LAN/SCSI/etc parts of the chip) Enable DMA/processing engines When done using the device, and perhaps the module needs to be unloaded, the driver needs to take the follow steps: Disable the device from generating IRQs Release the IRQ (free_irq()) Stop all DMA activity Release DMA buffers (both streaming and coherent) Unregister from other subsystems (e.g. scsi or netdev) Release MMIO/IOP resources Disable the device 

1. pci_register_driver()

首先我们需要注册PCI设备驱动，废话少说，直接看代码

/*/ /* Module management functions */ /*/ static int __init bt878_init_module(void) { 
    bt878_num = 0; printk(KERN_INFO "bt878: AUDIO driver version %d.%d.%d loaded\n", (BT878_VERSION_CODE >> 16) & 0xff, (BT878_VERSION_CODE >> 8) & 0xff, BT878_VERSION_CODE & 0xff); return pci_register_driver(&bt878_pci_driver); } static void __exit bt878_cleanup_module(void) { 
    pci_unregister_driver(&bt878_pci_driver); } module_init(bt878_init_module); module_exit(bt878_cleanup_module); 

下面我们看pci_register_driver(&bt878_pci_driver);

/* * pci_register_driver must be a macro so that KBUILD_MODNAME can be expanded */ #define pci_register_driver(driver) \ __pci_register_driver(driver, THIS_MODULE, KBUILD_MODNAME) 

__pci_register_driver（）函数如下

/ * __pci_register_driver - register a new pci driver * @drv: the driver structure to register * @owner: owner module of drv * @mod_name: module name string * * Adds the driver structure to the list of registered drivers. * Returns a negative value on error, otherwise 0. * If no error occurred, the driver remains registered even if * no device was claimed during registration. */ int __pci_register_driver(struct pci_driver *drv, struct module *owner, const char *mod_name) { 
    /* initialize common driver fields */ drv->driver.name = drv->name; drv->driver.bus = &pci_bus_type; drv->driver.owner = owner; drv->driver.mod_name = mod_name; drv->driver.groups = drv->groups; spin_lock_init(&drv->dynids.lock); INIT_LIST_HEAD(&drv->dynids.list); /* register with core */ return driver_register(&drv->driver); } EXPORT_SYMBOL(__pci_register_driver); 

driver_register(）函数如下

/ * driver_register - register driver with bus * @drv: driver to register * * We pass off most of the work to the bus_add_driver() call, * since most of the things we have to do deal with the bus * structures. */ int driver_register(struct device_driver *drv) { 
    int ret; struct device_driver *other; BUG_ON(!drv->bus->p); if ((drv->bus->probe && drv->probe) || (drv->bus->remove && drv->remove) || (drv->bus->shutdown && drv->shutdown)) printk(KERN_WARNING "Driver '%s' needs updating - please use " "bus_type methods\n", drv->name); other = driver_find(drv->name, drv->bus); if (other) { 
    printk(KERN_ERR "Error: Driver '%s' is already registered, " "aborting...\n", drv->name); return -EBUSY; } ret = bus_add_driver(drv); if (ret) return ret; ret = driver_add_groups(drv, drv->groups); if (ret) { 
    bus_remove_driver(drv); return ret; } kobject_uevent(&drv->p->kobj, KOBJ_ADD); return ret; } EXPORT_SYMBOL_GPL(driver_register); 

2.设备初始化

2.1 probe（）函数

static struct pci_driver bt878_pci_driver = { 
    .name = "bt878", .id_table = bt878_pci_tbl, .probe = bt878_probe, .remove = bt878_remove, }; 

再看bt878_probe函数的定义：

/*/ /* PCI device handling */ /*/ static int bt878_probe(struct pci_dev *dev, const struct pci_device_id *pci_id) { 
    int result = 0; unsigned char lat; struct bt878 *bt; unsigned int cardid; printk(KERN_INFO "bt878: Bt878 AUDIO function found (%d).\n", bt878_num); if (bt878_num >= BT878_MAX) { 
    printk(KERN_ERR "bt878: Too many devices inserted\n"); return -ENOMEM; } if (pci_enable_device(dev)) return -EIO; cardid = dev->subsystem_device << 16; cardid |= dev->subsystem_vendor; printk(KERN_INFO "%s: card id=[0x%x],[ %s ] has DVB functions.\n", __func__, cardid, card_name(pci_id)); bt = &bt878[bt878_num]; bt->dev = dev; bt->nr = bt878_num; bt->shutdown = 0; bt->id = dev->device; bt->irq = dev->irq; bt->bt878_adr = pci_resource_start(dev, 0); if (!request_mem_region(pci_resource_start(dev, 0), pci_resource_len(dev, 0), "bt878")) { 
    result = -EBUSY; goto fail0; } bt->revision = dev->revision; pci_read_config_byte(dev, PCI_LATENCY_TIMER, &lat); printk(KERN_INFO "bt878(%d): Bt%x (rev %d) at %02x:%02x.%x, ", bt878_num, bt->id, bt->revision, dev->bus->number, PCI_SLOT(dev->devfn), PCI_FUNC(dev->devfn)); printk("irq: %d, latency: %d, memory: 0x%lx\n", bt->irq, lat, bt->bt878_adr); #ifdef __sparc__ bt->bt878_mem = (unsigned char *) bt->bt878_adr; #else bt->bt878_mem = ioremap(bt->bt878_adr, 0x1000); #endif /* clear interrupt mask */ btwrite(0, BT848_INT_MASK); result = request_irq(bt->irq, bt878_irq, IRQF_SHARED, "bt878", (void *) bt); if (result == -EINVAL) { 
    printk(KERN_ERR "bt878(%d): Bad irq number or handler\n", bt878_num); goto fail1; } if (result == -EBUSY) { 
    printk(KERN_ERR "bt878(%d): IRQ %d busy, change your PnP config in BIOS\n", bt878_num, bt->irq); goto fail1; } if (result < 0) goto fail1; pci_set_master(dev); pci_set_drvdata(dev, bt); if ((result = bt878_mem_alloc(bt))) { 
    printk(KERN_ERR "bt878: failed to allocate memory!\n"); goto fail2; } bt878_make_risc(bt); btwrite(0, BT878_AINT_MASK); bt878_num++; return 0; fail2: free_irq(bt->irq, bt); fail1: release_mem_region(pci_resource_start(bt->dev, 0), pci_resource_len(bt->dev, 0)); fail0: pci_disable_device(dev); return result; } 

在这里我们重要讲解probe()的几个重要函数。

2.2 使能PCI设备

 if (pci_enable_device(dev)) return -EIO; 

那么这个函数主要是做什么呢，在这里摘录一段源代码中自带的文档中的说明：

Before touching any device registers, the driver needs to enable the PCI device by calling pci_enable_device(). This will: o wake up the device if it was in suspended state, o allocate I/O and memory regions of the device (if BIOS did not), o allocate an IRQ (if BIOS did not). 

翻译过来其实就是，唤醒设备，分配I/O和memory region,分配IRQ，好了我们接下来继续跟踪这个函数

/ * pci_enable_device - Initialize device before it's used by a driver. * @dev: PCI device to be initialized * * Initialize device before it's used by a driver. Ask low-level code * to enable I/O and memory. Wake up the device if it was suspended. * Beware, this function can fail. * * Note we don't actually enable the device many times if we call * this function repeatedly (we just increment the count). */ int pci_enable_device(struct pci_dev *dev) { 
    return pci_enable_device_flags(dev, IORESOURCE_MEM | IORESOURCE_IO); } EXPORT_SYMBOL(pci_enable_device); 

继续看pci_enable_device_flags（）函数

static int pci_enable_device_flags(struct pci_dev *dev, unsigned long flags) { 
    struct pci_dev *bridge; int err; int i, bars = 0; /* * Power state could be unknown at this point, either due to a fresh * boot or a device removal call. So get the current power state * so that things like MSI message writing will behave as expected * (e.g. if the device really is in D0 at enable time). */ if (dev->pm_cap) { 
    u16 pmcsr; pci_read_config_word(dev, dev->pm_cap + PCI_PM_CTRL, &pmcsr); dev->current_state = (pmcsr & PCI_PM_CTRL_STATE_MASK); } if (atomic_inc_return(&dev->enable_cnt) > 1) return 0; /* already enabled */ bridge = pci_upstream_bridge(dev); if (bridge) pci_enable_bridge(bridge); /* only skip sriov related */ for (i = 0; i <= PCI_ROM_RESOURCE; i++) if (dev->resource[i].flags & flags) bars |= (1 << i); for (i = PCI_BRIDGE_RESOURCES; i < DEVICE_COUNT_RESOURCE; i++) if (dev->resource[i].flags & flags) bars |= (1 << i); err = do_pci_enable_device(dev, bars); if (err < 0) atomic_dec(&dev->enable_cnt); return err; } 

重点看函数do_pci_enable_device()

 static int do_pci_enable_device(struct pci_dev *dev, int bars) { 
    int err; struct pci_dev *bridge; u16 cmd; u8 pin; err = pci_set_power_state(dev, PCI_D0); if (err < 0 && err != -EIO) return err; bridge = pci_upstream_bridge(dev); if (bridge) pcie_aspm_powersave_config_link(bridge); err = pcibios_enable_device(dev, bars); if (err < 0) return err; pci_fixup_device(pci_fixup_enable, dev); if (dev->msi_enabled || dev->msix_enabled) return 0; pci_read_config_byte(dev, PCI_INTERRUPT_PIN, &pin); if (pin) { 
    pci_read_config_word(dev, PCI_COMMAND, &cmd); if (cmd & PCI_COMMAND_INTX_DISABLE) pci_write_config_word(dev, PCI_COMMAND, cmd & ~PCI_COMMAND_INTX_DISABLE); } return 0; } 

看函数pci_set_power_state(dev, PCI_D0);

/ * pci_load_and_free_saved_state - Reload the save state pointed to by state, * and free the memory allocated for it. * @dev: PCI device that we're dealing with * 0 if the transition is to D1 or D2 but D1 and D2 are not supported. * 0 if device already is in the requested state. * 0 if the transition is to D3 but D3 is not supported. * 0 if device's power state has been successfully changed. */ int pci_set_power_state(struct pci_dev *dev, pci_power_t state) { 
    int error; /* bound the state we're entering */ if (state > PCI_D3cold) state = PCI_D3cold; else if (state < PCI_D0) state = PCI_D0; else if ((state == PCI_D1 || state == PCI_D2) && pci_no_d1d2(dev)) /* * If the device or the parent bridge do not support PCI PM, * ignore the request if we're doing anything other than putting * it into D0 (which would only happen on boot). */ return 0; /* Check if we're already there */ if (dev->current_state == state) return 0; __pci_start_power_transition(dev, state); /* This device is quirked not to be put into D3, so don't put it in D3 */ if (state >= PCI_D3hot && (dev->dev_flags & PCI_DEV_FLAGS_NO_D3)) return 0; /* * To put device in D3cold, we put device into D3hot in native * way, then put device into D3cold with platform ops */ error = pci_raw_set_power_state(dev, state > PCI_D3hot ? PCI_D3hot : state); if (!__pci_complete_power_transition(dev, state)) error = 0; return error; } EXPORT_SYMBOL(pci_set_power_state); 

err = pcibios_enable_device(dev, bars); if (err < 0) return err; 

 pci_read_config_byte(dev, PCI_INTERRUPT_PIN, &pin); if (pin) { 
    pci_read_config_word(dev, PCI_COMMAND, &cmd); if (cmd & PCI_COMMAND_INTX_DISABLE) pci_write_config_word(dev, PCI_COMMAND, cmd & ~PCI_COMMAND_INTX_DISABLE); } 

接下来我们讲另外一个函数

2.3 申请 MMIO/IOP 资源

我们看request_mem_region(pci_resource_start(dev, 0),pci_resource_len(dev, 0), “bt878”) 函数

/* these helpers provide future and backwards compatibility * for accessing popular PCI BAR info */ #define pci_resource_start(dev, bar) ((dev)->resource[(bar)].start) #define pci_resource_end(dev, bar) ((dev)->resource[(bar)].end) #define pci_resource_flags(dev, bar) ((dev)->resource[(bar)].flags) #define pci_resource_len(dev,bar) \ ((pci_resource_start((dev), (bar)) == 0 && \ pci_resource_end((dev), (bar)) == \ pci_resource_start((dev), (bar))) ? 0 : \ \ (pci_resource_end((dev), (bar)) - \ pci_resource_start((dev), (bar)) + 1)) 

其中 request_mem_region(）定义如下

#define request_mem_region(start,n,name) __request_region(&iomem_resource, (start), (n), (name), 0) 

接下来我们接着追函数

/ * @flags: IO resource flags */ struct resource * __request_region(struct resource *parent, resource_size_t start, resource_size_t n, const char *name, int flags) { 
    DECLARE_WAITQUEUE(wait, current); struct resource *res = alloc_resource(GFP_KERNEL); if (!res) return NULL; res->name = name; res->start = start; res->end = start + n - 1; write_lock(&resource_lock); for (;;) { 
    struct resource *conflict; res->flags = resource_type(parent) | resource_ext_type(parent); res->flags |= IORESOURCE_BUSY | flags; res->desc = parent->desc; conflict = __request_resource(parent, res); if (!conflict) break; if (conflict != parent) { 
    if (!(conflict->flags & IORESOURCE_BUSY)) { 
    parent = conflict; continue; } } if (conflict->flags & flags & IORESOURCE_MUXED) { 
    add_wait_queue(&muxed_resource_wait, &wait); write_unlock(&resource_lock); set_current_state(TASK_UNINTERRUPTIBLE); schedule(); remove_wait_queue(&muxed_resource_wait, &wait); write_lock(&resource_lock); continue; } /* Uhhuh, that didn't work out.. */ free_resource(res); res = NULL; break; } write_unlock(&resource_lock); return res; } EXPORT_SYMBOL(__request_region); 

2.4 申请注册中断函数

看函数

result = request_irq(bt->irq, bt878_irq, IRQF_SHARED, "bt878", (void *) bt); 

bt878_irq函数定义如下：

/*/ /* Interrupt service routine */ /*/ static irqreturn_t bt878_irq(int irq, void *dev_id) { 
    u32 stat, astat, mask; int count; struct bt878 *bt; bt = (struct bt878 *) dev_id; count = 0; while (1) { 
    stat = btread(BT878_AINT_STAT); mask = btread(BT878_AINT_MASK); if (!(astat = (stat & mask))) return IRQ_NONE; /* this interrupt is not for me */ /* dprintk("bt878(%d) debug: irq count %d, stat 0x%8.8x, mask 0x%8.8x\n",bt->nr,count,stat,mask); */ btwrite(astat, BT878_AINT_STAT); /* try to clear interrupt condition */ if (astat & (BT878_ASCERR | BT878_AOCERR)) { 
    if (bt878_verbose) { 
    printk(KERN_INFO "bt878(%d): irq%s%s risc_pc=%08x\n", bt->nr, (astat & BT878_ASCERR) ? " SCERR" : "", (astat & BT878_AOCERR) ? " OCERR" : "", btread(BT878_ARISC_PC)); } } if (astat & (BT878_APABORT | BT878_ARIPERR | BT878_APPERR)) { 
    if (bt878_verbose) { 
    printk(KERN_INFO "bt878(%d): irq%s%s%s risc_pc=%08x\n", bt->nr, (astat & BT878_APABORT) ? " PABORT" : "", (astat & BT878_ARIPERR) ? " RIPERR" : "", (astat & BT878_APPERR) ? " PPERR" : "", btread(BT878_ARISC_PC)); } } if (astat & (BT878_AFDSR | BT878_AFTRGT | BT878_AFBUS)) { 
    if (bt878_verbose) { 
    printk(KERN_INFO "bt878(%d): irq%s%s%s risc_pc=%08x\n", bt->nr, (astat & BT878_AFDSR) ? " FDSR" : "", (astat & BT878_AFTRGT) ? " FTRGT" : "", (astat & BT878_AFBUS) ? " FBUS" : "", btread(BT878_ARISC_PC)); } } if (astat & BT878_ARISCI) { 
    bt->finished_block = (stat & BT878_ARISCS) >> 28; tasklet_schedule(&bt->tasklet); break; } count++; if (count > 20) { 
    btwrite(0, BT878_AINT_MASK); printk(KERN_ERR "bt878(%d): IRQ lockup, cleared int mask\n", bt->nr); break; } } return IRQ_HANDLED; } 

2.5 使能DMA

看函数pci_set_master(dev);，官方说明如下

pci_set_master() will enable DMA by setting the bus master bit in the PCI_COMMAND register. It also fixes the latency timer value if it's set to something bogus by the BIOS. pci_clear_master() will disable DMA by clearing the bus master bit. 

跟踪代码如下：

/ * pci_set_master - enables bus-mastering for device dev * @dev: the PCI device to enable * * Enables bus-mastering on the device and calls pcibios_set_master() * to do the needed arch specific settings. */ void pci_set_master(struct pci_dev *dev) { 
    __pci_set_master(dev, true); pcibios_set_master(dev); } EXPORT_SYMBOL(pci_set_master); 

我们看函数__pci_set_master(dev, true);

 static void __pci_set_master(struct pci_dev *dev, bool enable) { 
    u16 old_cmd, cmd; pci_read_config_word(dev, PCI_COMMAND, &old_cmd); if (enable) cmd = old_cmd | PCI_COMMAND_MASTER; else cmd = old_cmd & ~PCI_COMMAND_MASTER; if (cmd != old_cmd) { 
    dev_dbg(&dev->dev, "%s bus mastering\n", enable ? "enabling" : "disabling"); pci_write_config_word(dev, PCI_COMMAND, cmd); } dev->is_busmaster = enable; } 

/ * pcibios_set_master - enable PCI bus-mastering for device dev * @dev: the PCI device to enable * * Enables PCI bus-mastering for the device. This is the default * implementation. Architecture specific implementations can override * this if necessary. */ void __weak pcibios_set_master(struct pci_dev *dev) { 
    u8 lat; /* The latency timer doesn't apply to PCIe (either Type 0 or Type 1) */ if (pci_is_pcie(dev)) return; pci_read_config_byte(dev, PCI_LATENCY_TIMER, &lat); if (lat < 16) lat = (64 <= pcibios_max_latency) ? 64 : pcibios_max_latency; else if (lat > pcibios_max_latency) lat = pcibios_max_latency; else return; pci_write_config_byte(dev, PCI_LATENCY_TIMER, lat); } 

这里有对latency timer value的处理。

2.6 分配 “consistent” 内存

看函数

 if ((result = bt878_mem_alloc(bt))) { 
    printk(KERN_ERR "bt878: failed to allocate memory!\n"); goto fail2; } 

我们看一下bt878_mem_alloc(struct bt878 *bt)函数

 static int bt878_mem_alloc(struct bt878 *bt) { 
    if (!bt->buf_cpu) { 
    bt->buf_size = 128 * 1024; bt->buf_cpu = pci_zalloc_consistent(bt->dev, bt->buf_size, &bt->buf_dma); if (!bt->buf_cpu) return -ENOMEM; } if (!bt->risc_cpu) { 
    bt->risc_size = PAGE_SIZE; bt->risc_cpu = pci_zalloc_consistent(bt->dev, bt->risc_size, &bt->risc_dma); if (!bt->risc_cpu) { 
    bt878_mem_free(bt); return -ENOMEM; } } return 0; } 

继续看函数pci_zalloc_consistent(）

static inline void * pci_zalloc_consistent(struct pci_dev *hwdev, size_t size, dma_addr_t *dma_handle) { 
    return dma_zalloc_coherent(hwdev == NULL ? NULL : &hwdev->dev, size, dma_handle, GFP_ATOMIC); } 

我们看函数继续看函数pci_zalloc_coherent(）函数

static inline void *dma_zalloc_coherent(struct device *dev, size_t size, dma_addr_t *dma_handle, gfp_t flag) { 
    void *ret = dma_alloc_coherent(dev, size, dma_handle, flag | __GFP_ZERO); return ret; } 

这样就分配好了

3 释放资源

我们看bt878_remove函数

static void bt878_remove(struct pci_dev *pci_dev) { 
    u8 command; struct bt878 *bt = pci_get_drvdata(pci_dev); if (bt878_verbose) printk(KERN_INFO "bt878(%d): unloading\n", bt->nr); /* turn off all capturing, DMA and IRQs */ btand(~0x13, BT878_AGPIO_DMA_CTL); /* first disable interrupts before unmapping the memory! */ btwrite(0, BT878_AINT_MASK); btwrite(~0U, BT878_AINT_STAT); /* disable PCI bus-mastering */ pci_read_config_byte(bt->dev, PCI_COMMAND, &command); /* Should this be &=~ ?? */ command &= ~PCI_COMMAND_MASTER; pci_write_config_byte(bt->dev, PCI_COMMAND, command); free_irq(bt->irq, bt); printk(KERN_DEBUG "bt878_mem: 0x%p.\n", bt->bt878_mem); if (bt->bt878_mem) iounmap(bt->bt878_mem); release_mem_region(pci_resource_start(bt->dev, 0), pci_resource_len(bt->dev, 0)); /* wake up any waiting processes because shutdown flag is set, no new processes (in this queue) are expected */ bt->shutdown = 1; bt878_mem_free(bt); pci_disable_device(pci_dev); return; }