【轉】linux spi子系統驅動分析

原文網址 ： http://blog.chinaunix.net/u2/66039/showart_1686204.html

 

     2.6.18內核下已經添加了完整的spi子系統了，參考mtd的分析，將從下到上層，再從上到下層的對其進行分析。

     以下先從下到上的進行分析：

     driver/spi下有兩個底層相關的spi驅動程序：
     spi_s3c24xx.c和spi_s3c24xx_gpio.c
     其中spi_s3c24xx.c是基於s3c24xx下相應的spi接口的驅動程序，spi_s3c24xx_gpio.c允許用戶指定3個gpio口，分別充當spi_clk、spi_mosi和spi_miso接口，模擬標準的spi總線。
     s3c2410自帶了兩個spi接口(spi0和spi1)，在此我只研究基於s3c2410下spi接口的驅動程序spi_s3c24xx.c。
     首先從spi驅動的檢測函數進行分析：
static int s3c24xx_spi_probe(struct platform_device *pdev) { struct s3c24xx_spi *hw; struct spi_master *master; struct spi_board_info *bi; struct resource *res; int err = 0; int i; /* pi_alloc_master函數申請了struct spi_master+struct s3c24xx_spi大小的數據， * spi_master_get_devdata和pi_master_get分別取出struct s3c24xx_spi和struct spi_master結構指針 */ master = spi_alloc_master(&pdev->dev, sizeof(struct s3c24xx_spi)); if (master == NULL) { dev_err(&pdev->dev, "No memory for spi_master/n"); err = -ENOMEM; goto err_nomem; } /* 填充struct spi_master結構 */ hw = spi_master_get_devdata(master); memset(hw, 0, sizeof(struct s3c24xx_spi)); hw->master = spi_master_get(master); hw->pdata = pdev->dev.platform_data; hw->dev = &pdev->dev; if (hw->pdata == NULL) { dev_err(&pdev->dev, "No platform data supplied/n"); err = -ENOENT; goto err_no_pdata; } platform_set_drvdata(pdev, hw);//dev_set_drvdata(&pdev->dev, hw) init_completion(&hw->done); /* setup the state for the bitbang driver */ /* 填充hw->bitbang結構(hw->bitbang結構充當一箇中間層，相當與input system的input_handle struct) */ hw->bitbang.master = hw->master; hw->bitbang.setup_transfer = s3c24xx_spi_setupxfer; hw->bitbang.chipselect = s3c24xx_spi_chipsel; hw->bitbang.txrx_bufs = s3c24xx_spi_txrx; hw->bitbang.master->setup = s3c24xx_spi_setup; dev_dbg(hw->dev, "bitbang at %p/n", &hw->bitbang); /* find and map our resources */ /* 申請spi所用到的資源：io、irq、時鐘等 */ res = platform_get_resource(pdev, IORESOURCE_MEM, 0); if (res == NULL) { dev_err(&pdev->dev, "Cannot get IORESOURCE_MEM/n"); err = -ENOENT; goto err_no_iores; } hw->ioarea = request_mem_region(res->start, (res->end - res->start)+1, pdev->name); if (hw->ioarea == NULL) { dev_err(&pdev->dev, "Cannot reserve region/n"); err = -ENXIO; goto err_no_iores; } hw->regs = ioremap(res->start, (res->end - res->start)+1); if (hw->regs == NULL) { dev_err(&pdev->dev, "Cannot map IO/n"); err = -ENXIO; goto err_no_iomap; } hw->irq = platform_get_irq(pdev, 0); if (hw->irq < 0) { dev_err(&pdev->dev, "No IRQ specified/n"); err = -ENOENT; goto err_no_irq; } err = request_irq(hw->irq, s3c24xx_spi_irq, 0, pdev->name, hw); if (err) { dev_err(&pdev->dev, "Cannot claim IRQ/n"); goto err_no_irq; } hw->clk = clk_get(&pdev->dev, "spi"); if (IS_ERR(hw->clk)) { dev_err(&pdev->dev, "No clock for device/n"); err = PTR_ERR(hw->clk); goto err_no_clk; } /* for the moment, permanently enable the clock */ clk_enable(hw->clk); /* program defaults into the registers */ /* 初始化spi相關的寄存器 */ writeb(0xff, hw->regs + S3C2410_SPPRE); writeb(SPPIN_DEFAULT, hw->regs + S3C2410_SPPIN); writeb(SPCON_DEFAULT, hw->regs + S3C2410_SPCON); /* add by lfc */ s3c2410_gpio_setpin(S3C2410_GPE13, 0); s3c2410_gpio_setpin(S3C2410_GPE12, 0); s3c2410_gpio_cfgpin(S3C2410_GPE13, S3C2410_GPE13_SPICLK0); s3c2410_gpio_cfgpin(S3C2410_GPE12, S3C2410_GPE12_SPIMOSI0); s3c2410_gpio_cfgpin(S3C2410_GPE11, S3C2410_GPE11_SPIMISO0); /* end add */ /* setup any gpio we can */ /* 片選 */ if (!hw->pdata->set_cs) { s3c2410_gpio_setpin(hw->pdata->pin_cs, 1); s3c2410_gpio_cfgpin(hw->pdata->pin_cs, S3C2410_GPIO_OUTPUT); } /* register our spi controller */ /* 最終通過調用spi_register_master來註冊spi控制器(驅動) */ err = spi_bitbang_start(&hw->bitbang); if (err) { dev_err(&pdev->dev, "Failed to register SPI master/n"); goto err_register; } dev_dbg(hw->dev, "shutdown=%d/n", hw->bitbang.shutdown); /* register all the devices associated */ /* 註冊所用使用本spi驅動的設備 */ bi = &hw->pdata->board_info[0]; for (i = 0; i < hw->pdata->board_size; i++, bi++) { dev_info(hw->dev, "registering %s/n", bi->modalias); bi->controller_data = hw; spi_new_device(master, bi); } return 0; err_register: clk_disable(hw->clk); clk_put(hw->clk); err_no_clk: free_irq(hw->irq, hw); err_no_irq: iounmap(hw->regs); err_no_iomap: release_resource(hw->ioarea); kfree(hw->ioarea); err_no_iores: err_no_pdata: spi_master_put(hw->master);; err_nomem: return err; } /* * spi_alloc_master - allocate SPI master controller * @dev: the controller, possibly using the platform_bus * @size: how much driver-private data to preallocate; the pointer to this * memory is in the class_data field of the returned class_device, * accessible with spi_master_get_devdata(). * * This call is used only by SPI master controller drivers, which are the * only ones directly touching chip registers. It's how they allocate * an spi_master structure, prior to calling spi_register_master(). * * This must be called from context that can sleep. It returns the SPI * master structure on success, else NULL. * * The caller is responsible for assigning the bus number and initializing * the master's methods before calling spi_register_master(); and (after errors * adding the device) calling spi_master_put() to prevent a memory leak. */ /*註釋已經寫得很清楚了，本函數旨在分配spi_master struct *其中，device爲主控制設備，size爲需要預分配的設備私有數據大小 *該函數被spi主控制器驅動所調用，用於在調用spi_register_master註冊主控制器前 *分配spi_master struct，分配bus number和初始化主控制器的操作方法 *注意在分配spi_master struct的時候多分配了大小爲size的設備私有數據 *並通過spi_master_set_devdata函數把其放到class_data field裏，以後可以通過spi_master_get_devdata來訪問 */ struct spi_master * __init_or_module spi_alloc_master(struct device *dev, unsigned size) { struct spi_master *master; if (!dev) return NULL; master = kzalloc(size + sizeof *master, SLAB_KERNEL); if (!master) return NULL; class_device_initialize(&master->cdev); master->cdev.class = &spi_master_class; master->cdev.dev = get_device(dev); spi_master_set_devdata(master, &master[1]); return master; } /* * spi_bitbang_start - start up a polled/bitbanging SPI master driver * @bitbang: driver handle * * Caller should have zero-initialized all parts of the structure, and then * provided callbacks for chip selection and I/O loops. If the master has * a transfer method, its final step should call spi_bitbang_transfer; or, * that's the default if the transfer routine is not initialized. It should * also set up the bus number and number of chipselects. * * For i/o loops, provide callbacks either per-word (for bitbanging, or for * hardware that basically exposes a shift register) or per-spi_transfer * (which takes better advantage of hardware like fifos or DMA engines). * * Drivers using per-word I/O loops should use (or call) spi_bitbang_setup and * spi_bitbang_cleanup to handle those spi master methods. Those methods are * the defaults if the bitbang->txrx_bufs routine isn't initialized. * * This routine registers the spi_master, which will process requests in a * dedicated task, keeping IRQs unblocked most of the time. To stop * processing those requests, call spi_bitbang_stop(). */ int spi_bitbang_start(struct spi_bitbang *bitbang) { int status; if (!bitbang->master || !bitbang->chipselect) return -EINVAL; /*bitbang_work * 初始化a work，後面再create_singlethread_workqueue， * 等到有數據要傳輸的時候，在spi_bitbang_transfer函數中通過調用queue_work(bitbang->workqueue, &bitbang->work) * 把work扔進workqueue中調度運行 * 這是內核的一貫做法，在mmc/sd驅動中也是這樣處理的^_^ */ INIT_WORK(&bitbang->work, bitbang_work, bitbang); /* 初始化自旋鎖和鏈表頭，以後用到 */ spin_lock_init(&bitbang->lock); spi_new_device INIT_LIST_HEAD(&bitbang->queue); if (!bitbang->master->transfer) bitbang->master->transfer = spi_bitbang_transfer;//spi數據的傳輸就是通過調用這個方法來實現的 /* spi_s3c24xx.c驅動中有相應的txrx_bufs處理方法，在bitbang_work中被調用 */ if (!bitbang->txrx_bufs) { bitbang->use_dma = 0; bitbang->txrx_bufs = spi_bitbang_bufs; if (!bitbang->master->setup) { if (!bitbang->setup_transfer) bitbang->setup_transfer = spi_bitbang_setup_transfer; bitbang->master->setup = spi_bitbang_setup; bitbang->master->cleanup = spi_bitbang_cleanup; } /* spi_s3c24xx.c驅動中有相應的setup處理方法，在稍後的spi_new_device中被調用 */ } else if (!bitbang->master->setup) return -EINVAL; /* this task is the only thing to touch the SPI bits */ bitbang->busy = 0; /* 創建工作者進程 */ bitbang->workqueue = create_singlethread_workqueue( bitbang->master->cdev.dev->bus_id); if (bitbang->workqueue == NULL) { status = -EBUSY; goto err1; } /* driver may get busy before register() returns, especially * if someone registered boardinfo for devices */ status = spi_register_master(bitbang->master); if (status < 0) goto err2; return status; err2: destroy_workqueue(bitbang->workqueue); err1: return status; } /** * spi_register_master - register SPI master controller * @master: initialized master, originally from spi_alloc_master() * * SPI master controllers connect to their drivers using some non-SPI bus, * such as the platform bus. The final stage of probe() in that code * includes calling spi_register_master() to hook up to this SPI bus glue. * * SPI controllers use board specific (often SOC specific) bus numbers, * and board-specific addressing for SPI devices combines those numbers * with chip select numbers. Since SPI does not directly support dynamic * device identification, boards need configuration tables telling which * chip is at which address. * * This must be called from context that can sleep. It returns zero on * success, else a negative error code (dropping the master's refcount). * After a successful return, the caller is responsible for calling * spi_unregister_master(). */ int __init_or_module spi_register_master(struct spi_master *master) { static atomic_t dyn_bus_id = ATOMIC_INIT((1<<16) - 1); struct device *dev = master->cdev.dev; int status = -ENODEV; int dynamic = 0; if (!dev) return -ENODEV; /* convention: dynamically assigned bus IDs count down from the max */ if (master->bus_num < 0) { master->bus_num = atomic_dec_return(&dyn_bus_id); dynamic = 1; } /* register the device, then userspace will see it. * registration fails if the bus ID is in use. */ snprintf(master->cdev.class_id, sizeof master->cdev.class_id, "spi%u", master->bus_num); status = class_device_add(&master->cdev);//註冊設備 if (status < 0) goto done; dev_dbg(dev, "registered master %s%s/n", master->cdev.class_id, dynamic ? " (dynamic)" : ""); /* populate children from any spi device tables */ scan_boardinfo(master); status = 0; done: return status; } /* FIXME someone should add support for a __setup("spi", ...) that * creates board info from kernel command lines */ /* * scan board_list for spi_board_info which is registered by spi_register_board_info * 很可惜，s3c24xx的spi驅動中不支持spi_register_board_info這種標準方式註冊方式，而是直接調用spi_new_device內部函數 */ static void __init_or_module scan_boardinfo(struct spi_master *master) { struct boardinfo *bi; struct device *dev = master->cdev.dev; down(&board_lock); list_for_each_entry(bi, &board_list, list) { struct spi_board_info *chip = bi->board_info; unsigned n; for (n = bi->n_board_info; n > 0; n--, chip++) { if (chip->bus_num != master->bus_num) continue; /* some controllers only have one chip, so they * might not use chipselects. otherwise, the * chipselects are numbered 0..max. */ if (chip->chip_select >= master->num_chipselect && master->num_chipselect) { dev_dbg(dev, "cs%d > max %d/n", chip->chip_select, master->num_chipselect); continue; } (void) spi_new_device(master, chip); } } up(&board_lock); } /* * Board-specific early init code calls this (probably during arch_initcall) * with segments of the SPI device table. Any device nodes are created later, * after the relevant parent SPI controller (bus_num) is defined. We keep * this table of devices forever, so that reloading a controller driver will * not make Linux forget about these hard-wired devices. * * Other code can also call this, e.g. a particular add-on board might provide * SPI devices through its expansion connector, so code initializing that board * would naturally declare its SPI devices. * * The board info passed can safely be __initdata ... but be careful of * any embedded pointers (platform_data, etc), they're copied as-is. */ int __init spi_register_board_info(struct spi_board_info const *info, unsigned n) { struct boardinfo *bi; bi = kmalloc(sizeof(*bi) + n * sizeof *info, GFP_KERNEL); if (!bi) return -ENOMEM; bi->n_board_info = n; memcpy(bi->board_info, info, n * sizeof *info); down(&board_lock); list_add_tail(&bi->list, &board_list); up(&board_lock); return 0; } /* On typical mainboards, this is purely internal; and it's not needed * after board init creates the hard-wired devices. Some development * platforms may not be able to use spi_register_board_info though, and * this is exported so that for example a USB or parport based adapter * driver could add devices (which it would learn about out-of-band). */ struct spi_device *__init_or_module spi_new_device(struct spi_master *master, struct spi_board_info *chip) { struct spi_device *proxy;//這個結構很重要，以後就是通過這個結構來操作實際的spi設備的 struct device *dev = master->cdev.dev; int status; /* NOTE: caller did any chip->bus_num checks necessary */ if (!spi_master_get(master)) return NULL; proxy = kzalloc(sizeof *proxy, GFP_KERNEL); if (!proxy) { dev_err(dev, "can't alloc dev for cs%d/n", chip->chip_select); goto fail; } /* 初始化spi_device 結構各成員 */ proxy->master = master; proxy->chip_select = chip->chip_select; proxy->max_speed_hz = chip->max_speed_hz; proxy->mode = chip->mode; proxy->irq = chip->irq; proxy->modalias = chip->modalias; snprintf(proxy->dev.bus_id, sizeof proxy->dev.bus_id, "%s.%u", master->cdev.class_id, chip->chip_select); proxy->dev.parent = dev; proxy->dev.bus = &spi_bus_type; proxy->dev.platform_data = (void *) chip->platform_data; proxy->controller_data = chip->controller_data; proxy->controller_state = NULL; proxy->dev.release = spidev_release; /* drivers may modify this default i/o setup */ /* 調用master->setup(即s3c24xx_spi_setup)函數初始化spi設備 */ status = master->setup(proxy); if (status < 0) { dev_dbg(dev, "can't %s %s, status %d/n", "setup", proxy->dev.bus_id, status); goto fail; } /* driver core catches callers that misbehave by defining * devices that already exist. */ status = device_register(&proxy->dev);//真正註冊原始設備 if (status < 0) { dev_dbg(dev, "can't %s %s, status %d/n", "add", proxy->dev.bus_id, status); goto fail; } dev_dbg(dev, "registered child %s/n", proxy->dev.bus_id); return proxy; fail: spi_master_put(master); kfree(proxy); return NULL; } static int s3c24xx_spi_setup(struct spi_device *spi) { int ret; /* 進行一些檢查性操作 */ if (!spi->bits_per_word) spi->bits_per_word = 8; if ((spi->mode & SPI_LSB_FIRST) != 0) return -EINVAL; ret = s3c24xx_spi_setupxfer(spi, NULL); if (ret < 0) { dev_err(&spi->dev, "setupxfer returned %d/n", ret); return ret; } dev_dbg(&spi->dev, "%s: mode %d, %u bpw, %d hz/n", __FUNCTION__, spi->mode, spi->bits_per_word, spi->max_speed_hz); return 0; } static int s3c24xx_spi_setupxfer(struct spi_device *spi, struct spi_transfer *t) { struct s3c24xx_spi *hw = to_hw(spi); unsigned int bpw; unsigned int hz; unsigned int div; bpw = t ? t->bits_per_word : spi->bits_per_word; hz = t ? t->speed_hz : spi->max_speed_hz; if (bpw != 8) { dev_err(&spi->dev, "invalid bits-per-word (%d)/n", bpw); return -EINVAL; } div = clk_get_rate(hw->clk) / hz; /* is clk = pclk / (2 * (pre+1)), or is it * clk = (pclk * 2) / ( pre + 1) */ div = (div / 2) - 1;//求出預分頻值 if (div < 0) div = 1; if (div > 255) div = 255; dev_dbg(&spi->dev, "setting pre-scaler to %d (hz %d)/n", div, hz); writeb(div, hw->regs + S3C2410_SPPRE);//設置預分頻值 spin_lock(&hw->bitbang.lock); if (!hw->bitbang.busy) { hw->bitbang.chipselect(spi, BITBANG_CS_INACTIVE);//修改時鐘，先禁用spi /* need to ndelay for 0.5 clocktick ? */ } spin_unlock(&hw->bitbang.lock); return 0; } static void s3c24xx_spi_chipsel(struct spi_device *spi, int value) { struct s3c24xx_spi *hw = to_hw(spi); unsigned int cspol = spi->mode & SPI_CS_HIGH ? 1 : 0; unsigned int spcon; switch (value) { case BITBANG_CS_INACTIVE: /* 禁用spi(禁用片選) */ if (hw->pdata->set_cs) hw->pdata->set_cs(hw->pdata, value, cspol); else s3c2410_gpio_setpin(hw->pdata->pin_cs, cspol ^ 1); break; case BITBANG_CS_ACTIVE: /* * 啓用spi：根據需要設置寄存器並啓用使能片選 * (如果spi_board_info中沒有設置相應的mode選項的話，那就只能使用默認值SPPIN_DEFAULT和SPCON_DEFAULT了) */ spcon = readb(hw->regs + S3C2410_SPCON); if (spi->mode & SPI_CPHA) spcon |= S3C2410_SPCON_CPHA_FMTB; else spcon &= ~S3C2410_SPCON_CPHA_FMTB; if (spi->mode & SPI_CPOL) spcon |= S3C2410_SPCON_CPOL_HIGH; else spcon &= ~S3C2410_SPCON_CPOL_HIGH; spcon |= S3C2410_SPCON_ENSCK; /* write new configration */ writeb(spcon, hw->regs + S3C2410_SPCON); if (hw->pdata->set_cs) hw->pdata->set_cs(hw->pdata, value, cspol); else s3c2410_gpio_setpin(hw->pdata->pin_cs, cspol); break; } }

 

     好了，至此spi主控制器(驅動)和板上spi設備註冊完畢，以後要使用spi來傳輸數據的話，只要先獲得spi設備結構，然後就可以利用它來和spi驅動打交道了(就好像你要操作一個文件，先要獲取文件句柄一樣，明白吧^_^)