SPI子系统分析之四:驱动模块

内核版本:3.9.5

SPI控制器层(平台相关)

上一节讲了SPI核心层的注册和匹配函数,它是平台无关的.正是在核心层抽象了SPI控制器层的相同部分然后提供了统一的API给SPI设备层来使用.我们这一节就能看到,一个SPI控制器以platform_device的形式注册进内核,并且调用spi_register_board_info函数注册了spi_board_info结构.我们前面说过,struct spi_board_info结构是对spi_device的描述,其中的内从最终是要用来初始化struct spi_device实例的.

哎!闲话少说了,越说越糊涂.我们以davinci的dm365平台为例,来看看SPI控制器的相关内容.在arch/arm/mach-davinci/board-dm365-evm.c中有:

 1 static struct spi_board_info dm365_evm_spi_info[] __initconst = {
 2     {
 3         .modalias    = "at25",
 4         .platform_data    = &at25640,
 5         .max_speed_hz    = 10 * 1000 * 1000,
 6         .bus_num    = 0,
 7         .chip_select    = 0,
 8         .mode        = SPI_MODE_0,
 9     },
10 };
11 
12 static __init void dm365_evm_init(void)
13 {
14     ……
15     dm365_init_spi0(BIT(0), dm365_evm_spi_info,
16             ARRAY_SIZE(dm365_evm_spi_info));
17 }

dm365_evm_init这个函数是dm365平台初始化函数,我略去了和SPI无关的部分.可以看到其中调用了dm365_init_spi0函数,并且将一个struct spi_board_info这个结构类型的数组作为参数传了进去.那么来看看dm365_init_spi0函数,在arch/arm/mach-davinci/dm365.c中:

 1 static u64 dm365_spi0_dma_mask = DMA_BIT_MASK(32);
 2 
 3 static struct davinci_spi_platform_data dm365_spi0_pdata = {
 4     .version     = SPI_VERSION_1,
 5     .num_chipselect = 2,
 6     .dma_event_q    = EVENTQ_3,
 7 };
 8 
 9 static struct resource dm365_spi0_resources[] = {
10     {
11         .start = 0x01c66000,
12         .end   = 0x01c667ff,
13         .flags = IORESOURCE_MEM,
14     },
15     {
16         .start = IRQ_DM365_SPIINT0_0,
17         .flags = IORESOURCE_IRQ,
18     },
19     {
20         .start = 17,
21         .flags = IORESOURCE_DMA,
22     },
23     {
24         .start = 16,
25         .flags = IORESOURCE_DMA,
26     },
27 };
28 
29 static struct platform_device dm365_spi0_device = {
30     .name = "spi_davinci",/*这个是和platform_driver匹配的依据,具体到davinci的板子就是davinci_spi_driver*/
31     .id = 0,/*对于SPI,这个值最后会在初始化spi_master的时候用来初始化master->bus_num*/
32     .dev = {
33         .dma_mask = &dm365_spi0_dma_mask,
34         .coherent_dma_mask = DMA_BIT_MASK(32),
35         .platform_data = &dm365_spi0_pdata,
36     },
37     .num_resources = ARRAY_SIZE(dm365_spi0_resources),
38     .resource = dm365_spi0_resources,
39 };
40 
41 void __init dm365_init_spi0(unsigned chipselect_mask,
42         const struct spi_board_info *info, unsigned len)
43 {
44     davinci_cfg_reg(DM365_SPI0_SCLK);
45     davinci_cfg_reg(DM365_SPI0_SDI);
46     davinci_cfg_reg(DM365_SPI0_SDO);
47 
48     /* not all slaves will be wired up */
49     if (chipselect_mask & BIT(0))
50         davinci_cfg_reg(DM365_SPI0_SDENA0);
51     if (chipselect_mask & BIT(1))
52         davinci_cfg_reg(DM365_SPI0_SDENA1);
53 
54     spi_register_board_info(info, len);
55 
56     platform_device_register(&dm365_spi0_device);
57 }

第54行注册了struct spi_board_info实例,就是我们传进来的dm365_evm_spi_info.在设备移植时填充结构体spi_board_info是移植的重要工作.我们来看看这个函数的实现,在drivers/spi/spi.c中:

 1 int spi_register_board_info(struct spi_board_info const *info, unsigned n)
 2 {
 3     struct boardinfo *bi;
 4     int i;
 5 
 6     bi = kzalloc(n * sizeof(*bi), GFP_KERNEL);/*为结构体boardinfo分配内存空间*/
 7     if (!bi)
 8         return -ENOMEM;
 9 
10     for (i = 0; i < n; i++, bi++, info++) {
11         struct spi_master *master;
12 
13         memcpy(&bi->board_info, info, sizeof(*info));
14         mutex_lock(&board_lock);
15         list_add_tail(&bi->list, &board_list);/*添加到板级描述符链表*/
16         list_for_each_entry(master, &spi_master_list, list)/*将SPI主机控制类链表所有的节点匹配板级信息的设备初始化*/
17             spi_match_master_to_boardinfo(master, &bi->board_info);
18         mutex_unlock(&board_lock);
19     }
20 
21     return 0;
22 }

这里又看到了一个结构struct boardinfo,其实它简单的就像没穿裤子的女人,我们来看,在同文件中:

 1 struct boardinfo {
 2     struct list_head    list;
 3     struct spi_board_info    board_info;
 4 };
 5 
 6 static LIST_HEAD(board_list);
 7 static LIST_HEAD(spi_master_list);
 8 
 9 /*
10  * Used to protect add/del opertion for board_info list and
11  * spi_master list, and their matching process
12  */
13 /*boardinfo链表操作锁*/
14 static DEFINE_MUTEX(board_lock);

这个结构是一个板级相关信息链表,就是说它是一些描述spi_device的信息的集合.结构体boardinfo管理多个结构体spi_board_info,结构体spi_board_info中挂在SPI总线上的设备的平台信息.一个结构体spi_board_info对应着一个SPI设备spi_device.
同时我们也看到了,函数中出现的board_list和spi_master_list都是全局的链表,她们分别记录了系统中所有的boardinfo和所有的spi_master.至于spi_match_master_to_boardinfo函数是什么意思,我们后面还会遇到,到时候再讲.
dm365_init_spi0函数中第56行注册平台设备.我们看到这个platform_device的的name是"spi_davinci",那么就必然还存在一个名为"spi_davinci"的platform_driver.那好办了,搜一下发现在drivers/spi/spi_davinci.c中:

 1 static struct platform_driver davinci_spi_driver = {
 2     .driver = {
 3         .name = "spi_davinci",
 4         .owner = THIS_MODULE,
 5         .of_match_table = davinci_spi_of_match,
 6     },
 7     .probe = davinci_spi_probe,
 8     .remove = davinci_spi_remove,
 9 };
10 module_platform_driver(davinci_spi_driver);

Linux设备模型常识告诉我们,当系统中注册了一个名为"spi_davinci"的platform_device时,同时又住了一个名为"spi_davinci"的platform_driver.那么就会执行这里的probe回调.这里我们来看davinci_spi_probe函数.

  1 static int davinci_spi_probe(struct platform_device *pdev)
  2 {
  3     struct spi_master *master;
  4     struct davinci_spi *dspi;/*davinci_spi这个结构用来描述具体的davinci平台上的spi控制器,等于说是对spi_master的一个封装*/
  5     struct davinci_spi_platform_data *pdata;
  6     struct resource *r, *mem;
  7     resource_size_t dma_rx_chan = SPI_NO_RESOURCE;
  8     resource_size_t    dma_tx_chan = SPI_NO_RESOURCE;
  9     int i = 0, ret = 0;
 10     u32 spipc0;
 11 
 12     /*分配master结构体,其中包括davinci_spi结构的内存空间,使用master.dev.driver_data指向它*/
 13     master = spi_alloc_master(&pdev->dev, sizeof(struct davinci_spi));
 14     if (master == NULL) {
 15         ret = -ENOMEM;
 16         goto err;
 17     }
 18 
 19     dev_set_drvdata(&pdev->dev, master);/*pdev->dev.device_private->driver_data = master*/
 20 
 21     dspi = spi_master_get_devdata(master);/*就是获取上文master.dev.driver_data指向的对象地址,其实就是davinci_spi结构对象的空间地址,将
 22     其赋给dspi*/
 23     if (dspi == NULL) {/*dspi不能为空哦*/
 24         ret = -ENOENT;
 25         goto free_master;
 26     }
 27 
 28     /*下面这几行就是填充dspi的pdata字段*/
 29     if (pdev->dev.platform_data) {
 30         pdata = pdev->dev.platform_data;/*具体到对于dm365来说就是dm365_spi0_pdata*/
 31         dspi->pdata = *pdata;
 32     } else {
 33         /* update dspi pdata with that from the DT */
 34         ret = spi_davinci_get_pdata(pdev, dspi);
 35         if (ret < 0)
 36             goto free_master;
 37     }
 38 
 39     /* pdata in dspi is now updated and point pdata to that */
 40     pdata = &dspi->pdata;/*pdata指针再指向dspi->pdata*/
 41 
 42     r = platform_get_resource(pdev, IORESOURCE_MEM, 0);/*获取IO资源*/
 43     if (r == NULL) {
 44         ret = -ENOENT;
 45         goto free_master;
 46     }
 47 
 48     dspi->pbase = r->start;
 49 
 50     mem = request_mem_region(r->start, resource_size(r), pdev->name);/*申请IO内存*/
 51     if (mem == NULL) {
 52         ret = -EBUSY;
 53         goto free_master;
 54     }
 55 
 56     dspi->base = ioremap(r->start, resource_size(r));/*建立内存映射*/
 57     if (dspi->base == NULL) {
 58         ret = -ENOMEM;
 59         goto release_region;
 60     }
 61 
 62     dspi->irq = platform_get_irq(pdev, 0);/*获取irq号*/
 63     if (dspi->irq <= 0) {
 64         ret = -EINVAL;
 65         goto unmap_io;
 66     }
 67 
 68     ret = request_threaded_irq(dspi->irq, davinci_spi_irq, dummy_thread_fn,
 69                  0, dev_name(&pdev->dev), dspi);/*申请spi中断,中断处理函数为davinci_spi_irq*/
 70     if (ret)
 71         goto unmap_io;
 72 
 73     /*设置bitbang的所属master*/
 74     dspi->bitbang.master = spi_master_get(master);
 75     if (dspi->bitbang.master == NULL) {
 76         ret = -ENODEV;
 77         goto irq_free;
 78     }
 79 
 80     dspi->clk = clk_get(&pdev->dev, NULL);/*获取spi时钟*/
 81     if (IS_ERR(dspi->clk)) {
 82         ret = -ENODEV;
 83         goto put_master;
 84     }
 85     clk_prepare_enable(dspi->clk);
 86 
 87     master->dev.of_node = pdev->dev.of_node;
 88     master->bus_num = pdev->id;/*bus_num*/
 89     master->num_chipselect = pdata->num_chipselect;/*保存SPI主机控制器支持的片选数量.具体到dm365可以看到dm365_spi0_pdata中将其定义为2*/
 90     master->setup = davinci_spi_setup;
 91 
 92     /*设置bitbang控制传输的相关函数*/
 93     dspi->bitbang.chipselect = davinci_spi_chipselect;
 94     dspi->bitbang.setup_transfer = davinci_spi_setup_transfer;
 95 
 96     dspi->version = pdata->version;/*具体到dm365可以看到dm365_spi0_pdata中将其定义为0*/
 97 
 98     dspi->bitbang.flags = SPI_NO_CS | SPI_LSB_FIRST | SPI_LOOP;
 99     if (dspi->version == SPI_VERSION_2)
100         dspi->bitbang.flags |= SPI_READY;
101 
102     r = platform_get_resource(pdev, IORESOURCE_DMA, 0);/*获取DMA资源,这作为输入缓冲*/
103     if (r)
104         dma_rx_chan = r->start;
105     r = platform_get_resource(pdev, IORESOURCE_DMA, 1);/*由参数就能知道davinci的DMA资源定义了两个,这里就获取第二个.这作为输出缓冲*/
106     if (r)
107         dma_tx_chan = r->start;
108 
109     dspi->bitbang.txrx_bufs = davinci_spi_bufs;/*传输数据最终要调用的函数*/
110     if (dma_rx_chan != SPI_NO_RESOURCE &&
111         dma_tx_chan != SPI_NO_RESOURCE) {
112         dspi->dma_rx_chnum = dma_rx_chan;
113         dspi->dma_tx_chnum = dma_tx_chan;
114 
115         ret = davinci_spi_request_dma(dspi);
116         if (ret)
117             goto free_clk;
118 
119         dev_info(&pdev->dev, "DMA: supported\n");
120         dev_info(&pdev->dev, "DMA: RX channel: %d, TX channel: %d, "
121                 "event queue: %d\n", dma_rx_chan, dma_tx_chan,
122                 pdata->dma_event_q);
123     }
124 
125     dspi->get_rx = davinci_spi_rx_buf_u8;
126     dspi->get_tx = davinci_spi_tx_buf_u8;
127 
128     init_completion(&dspi->done);/*初始化completion,用于实现同步I/O*/
129 
130     /* Reset In/OUT SPI module */
131     iowrite32(0, dspi->base + SPIGCR0);
132     udelay(100);
133     iowrite32(1, dspi->base + SPIGCR0);
134 
135     /* Set up SPIPC0.  CS and ENA init is done in davinci_spi_setup */
136     spipc0 = SPIPC0_DIFUN_MASK | SPIPC0_DOFUN_MASK | SPIPC0_CLKFUN_MASK;
137     iowrite32(spipc0, dspi->base + SPIPC0);
138 
139     /* initialize chip selects */
140     if (pdata->chip_sel) {/*davinci的pdata中chip_sel字段并没有设置,这里为空,因此不会进来*/
141         for (i = 0; i < pdata->num_chipselect; i++) {
142             if (pdata->chip_sel[i] != SPI_INTERN_CS)
143                 gpio_direction_output(pdata->chip_sel[i], 1);
144         }
145     }
146 
147     if (pdata->intr_line)/*dm365这个字段为空*/
148         iowrite32(SPI_INTLVL_1, dspi->base + SPILVL);
149     else
150         iowrite32(SPI_INTLVL_0, dspi->base + SPILVL);
151 
152     iowrite32(CS_DEFAULT, dspi->base + SPIDEF);
153 
154     /* master mode default */
155     set_io_bits(dspi->base + SPIGCR1, SPIGCR1_CLKMOD_MASK);
156     set_io_bits(dspi->base + SPIGCR1, SPIGCR1_MASTER_MASK);/*默认设置SPI主控制器工作在master方式*/
157     set_io_bits(dspi->base + SPIGCR1, SPIGCR1_POWERDOWN_MASK);
158 
159     ret = spi_bitbang_start(&dspi->bitbang);/*注册我们的主机SPI控制器*/
160     if (ret)
161         goto free_dma;
162 
163     dev_info(&pdev->dev, "Controller at 0x%p\n", dspi->base);
164 
165     return ret;
166 
167 free_dma:
168     dma_release_channel(dspi->dma_rx);
169     dma_release_channel(dspi->dma_tx);
170 free_clk:
171     clk_disable_unprepare(dspi->clk);
172     clk_put(dspi->clk);
173 put_master:
174     spi_master_put(master);/*减少引用计数*/
175 irq_free:
176     free_irq(dspi->irq, dspi);
177 unmap_io:
178     iounmap(dspi->base);
179 release_region:
180     release_mem_region(dspi->pbase, resource_size(r));
181 free_master:
182     kfree(master);
183 err:
184     return ret;
185 }

该函数首先为spi_master结构体以及davinci_spi结构体分配了空间,同时,spi_master.dev.driver_data指向了davinci_spi.接着执行了该条语句:

pdata = pdev->dev.platform_data;/*具体到对于dm365来说就是dm365_spi0_pdata*/

dspi->pdata = *pdata;

NOTE:在这里获取platform_device.dev.platform_data,也就是平台设备的相关数据,这是平台设备移植最需要关注的地方.

随后,为master定义了setup方法,为bitbang定义了3个方法.之后获取了一系列的资源,同时注册了中断服务程序.接着再初始化了completion,这个东东将用于实现同步I/O,他的伟大之处后面会体现出来的.最后调用spi_bitbang_start注册主机控制器.我们来看这个函数,在drivers/spi/spi_bitbang.c中:

 1 int spi_bitbang_start(struct spi_bitbang *bitbang)
 2 {
 3     struct spi_master *master = bitbang->master;
 4     int status;
 5 
 6     if (!master || !bitbang->chipselect)
 7         return -EINVAL;
 8 
 9     INIT_WORK(&bitbang->work, bitbang_work);/*初始化一个struct work,处理函数为bitbang_work*/
10     spin_lock_init(&bitbang->lock);/*初始化自旋锁*/
11     INIT_LIST_HEAD(&bitbang->queue);/*初始化链表头,链表为双向循环链表*/
12 
13     if (!master->mode_bits)
14         master->mode_bits = SPI_CPOL | SPI_CPHA | bitbang->flags;
15 
16     /*检测bitbang中的函数是否都定义了,如果没定义,则默认使用spi_bitbang_xxx*/
17     if (!master->transfer)/*master的transfer方法没有定义过*/
18         master->transfer = spi_bitbang_transfer;/*使用默认的spi_bitbang_transfe方法*/
19     if (!bitbang->txrx_bufs) {/*如果bitbang没有txrx_bufs方法,其实对于davinci在davinci_spi_probe函数中定义过该方法*/
20         bitbang->use_dma = 0;
21         bitbang->txrx_bufs = spi_bitbang_bufs;
22         if (!master->setup) {
23             if (!bitbang->setup_transfer)
24                 bitbang->setup_transfer =
25                      spi_bitbang_setup_transfer;
26             master->setup = spi_bitbang_setup;
27             master->cleanup = spi_bitbang_cleanup;
28         }
29     } else if (!master->setup)/*对于davinci在davinci_spi_probe函数中定义过该方法*/
30         return -EINVAL;
31     if (master->transfer == spi_bitbang_transfer &&
32             !bitbang->setup_transfer)
33         return -EINVAL;
34 
35     /* this task is the only thing to touch the SPI bits */
36     bitbang->busy = 0;
37     bitbang->workqueue = create_singlethread_workqueue(
38             dev_name(master->dev.parent));/*创建bitbang的工作队列*/
39     if (bitbang->workqueue == NULL) {
40         status = -EBUSY;
41         goto err1;
42     }
43 
44     /* driver may get busy before register() returns, especially
45      * if someone registered boardinfo for devices
46      */
47     status = spi_register_master(master);/*注册spi控制器*/
48     if (status < 0)
49         goto err2;
50 
51     return status;
52 
53 err2:
54     destroy_workqueue(bitbang->workqueue);
55 err1:
56     return status;
57 }
58 EXPORT_SYMBOL_GPL(spi_bitbang_start);

定义了控制器的transfer方法为spi_bitbang_transfer.创建了一个工作队列和一个工作bitbang_work,同时创建了一个链表.这些东东后面都会看到.最后,调用了spi_register_master函数,该函数将完成SPI控制器的注册,其中还牵涉到spi_device的注册.我们来看看这个函数.下列函数位于drivers/spi/spi.c:

 1 int spi_register_master(struct spi_master *master)
 2 {
 3     static atomic_t        dyn_bus_id = ATOMIC_INIT((1<<15) - 1);
 4     struct device        *dev = master->dev.parent;
 5     struct boardinfo    *bi;
 6     int            status = -ENODEV;
 7     int            dynamic = 0;
 8 
 9     if (!dev)
10         return -ENODEV;
11 
12     status = of_spi_register_master(master);
13     if (status)
14         return status;
15 
16     /* even if it's just one always-selected device, there must
17      * be at least one chipselect
18      */
19     if (master->num_chipselect == 0)/*SPI主控制器支持的片选数当然不能为0,否则还怎么挂接从设备啊.一个接口对应一个master,一个master对应
20     一条SPI总线,一条总线上可能挂有多个设备,num_chipselect就表示该总线上的设备数*/
21         return -EINVAL;
22 
23     if ((master->bus_num < 0) && master->dev.of_node)
24         master->bus_num = of_alias_get_id(master->dev.of_node, "spi");
25 
26     /* convention:  dynamically assigned bus IDs count down from the max */
27     if (master->bus_num < 0) {/*总线号从最大开始减*/
28         /* FIXME switch to an IDR based scheme, something like
29          * I2C now uses, so we can't run out of "dynamic" IDs
30          */
31         master->bus_num = atomic_dec_return(&dyn_bus_id);
32         dynamic = 1;
33     }
34 
35     spin_lock_init(&master->bus_lock_spinlock);
36     mutex_init(&master->bus_lock_mutex);
37     master->bus_lock_flag = 0;/*这个标志指示SPI总线是否被锁*/
38 
39     /* register the device, then userspace will see it.
40      * registration fails if the bus ID is in use.
41      */
42     dev_set_name(&master->dev, "spi%u", master->bus_num);
43     status = device_add(&master->dev);/*向内核注册设备*/
44     if (status < 0)
45         goto done;
46     dev_dbg(dev, "registered master %s%s\n", dev_name(&master->dev),
47             dynamic ? " (dynamic)" : "");
48 
49     /* If we're using a queued driver, start the queue */
50     if (master->transfer)/*对于具体到davinci,此字段在spi_bitbang_start中被初始化为spi_bitbang_transfer*/
51         dev_info(dev, "master is unqueued, this is deprecated\n");
52     else {
53         status = spi_master_initialize_queue(master);
54         if (status) {
55             device_unregister(&master->dev);
56             goto done;
57         }
58     }
59 
60     mutex_lock(&board_lock);
61     list_add_tail(&master->list, &spi_master_list);/*把这个SPI主机控制器添加进全局的spi_master_list链表*/
62     list_for_each_entry(bi, &board_list, list)/*遍历全局的board_list链表,为每一个boardinfo结构节点查找其中的指向的spi_board_info结构,通过
63     对spi_board_info的bus_bum和SPI主机控制器(spi_master)的bus_num进行匹配,来确定SPI从设备是否由此SPI主机控制器来控制.如果匹配,则通
64     过调用spi_new_device函数创建spi_device从设备,并且将其注册进内核*/
65         spi_match_master_to_boardinfo(master, &bi->board_info);
66     mutex_unlock(&board_lock);
67 
68     /* Register devices from the device tree and ACPI */
69     of_register_spi_devices(master);
70     acpi_register_spi_devices(master);
71 done:
72     return status;
73 }
74 EXPORT_SYMBOL_GPL(spi_register_master);

该函数注释一目了然,我们来看看spi_match_master_to_boardinfo这个函数吧.在同文件中有:

 1 /*使用SPI主控制类和板级信息匹配则添加一个新设备*/
 2 static void spi_match_master_to_boardinfo(struct spi_master *master,
 3                 struct spi_board_info *bi)
 4 {
 5     struct spi_device *dev;
 6 
 7     if (master->bus_num != bi->bus_num)/*通过bus_num对spi设备和master进行匹配*/
 8         return;
 9 
10     dev = spi_new_device(master, bi);/*执行到此,表示匹配完成,SPI设备由该SPI接口来控制,开始创建spi_device*/
11     if (!dev)
12         dev_err(master->dev.parent, "can't create new device for %s\n",
13             bi->modalias);
14 }

地球人都知道这段代码什么意思,好了继续看spi_new_device函数.在同文件中:

 1 struct spi_device *spi_new_device(struct spi_master *master,
 2                   struct spi_board_info *chip)
 3 {
 4     struct spi_device    *proxy;
 5     int            status;
 6 
 7     /* NOTE:  caller did any chip->bus_num checks necessary.
 8      *
 9      * Also, unless we change the return value convention to use
10      * error-or-pointer (not NULL-or-pointer), troubleshootability
11      * suggests syslogged diagnostics are best here (ugh).
12      */
13 
14     proxy = spi_alloc_device(master);/*分配spi_device结构,并初始化一些字段*/
15     if (!proxy)
16         return NULL;
17 
18     WARN_ON(strlen(chip->modalias) >= sizeof(proxy->modalias));
19 
20     /*从spi_board_info获取SPI从设备的参数*/
21     proxy->chip_select = chip->chip_select;
22     proxy->max_speed_hz = chip->max_speed_hz;
23     proxy->mode = chip->mode;
24     proxy->irq = chip->irq;
25     strlcpy(proxy->modalias, chip->modalias, sizeof(proxy->modalias));
26     proxy->dev.platform_data = (void *) chip->platform_data;
27     proxy->controller_data = chip->controller_data;
28     proxy->controller_state = NULL;
29 
30     status = spi_add_device(proxy);/*将新设备添加进内核*/
31     if (status < 0) {
32         spi_dev_put(proxy);/*从内核模块中撤销这个SPI(从)设备,但是这貌似并没有释放spi_alloc_device开辟的内存.实质上这个函数只是减少
33     了SPI(从)设备的引用计数*/
34         return NULL;
35     }
36 
37     return proxy;
38 }
39 EXPORT_SYMBOL_GPL(spi_new_device);

这个函数首先创建了spi_device结构,让后通过板级信息spi_board_info将SPI从设备的相关信息复制给spi_device结构,从而完成了spi_device结构的定义,最后调用spi_add_device,完成spi_device的注册.其中struct spi_board_info *chip这就是我们当初arch/arm/mach-davinci/board-dm365-evm.c中定义的dm365_evm_spi_info数组中的结构实例.

第25行我们就知道,这里注册的spi_device的modalias字段就被初始化为"at25".那么与其对应的spi_driver的device_driver中的name字段肯定为"at25".只有这样才能在SPI核心层的spi_match_device函数中匹配.搜了一遍内核,看到在drivers/msic/eeprom/at25.c中有:

 1 static struct spi_driver at25_driver = {
 2     .driver = {
 3         .name        = "at25",
 4         .owner        = THIS_MODULE,
 5     },
 6     .probe        = at25_probe,/*与相应的SPI(从)设备spi_device匹配成功后,则调用这里的probe函数*/
 7     .remove        = at25_remove,
 8 };
 9 
10 module_spi_driver(at25_driver);

第10行这个宏是SPI架构专门定义的,在include/linux/spi/spi.h中,我们来看:

1 #define module_spi_driver(__spi_driver) \
2     module_driver(__spi_driver, spi_register_driver, \
3             spi_unregister_driver)

让暴风雨来的更猛烈些吧,研究内核的孩纸都伤不起啊,我们只有硬着头皮往下看,在include/linux/device.h中:

 1 #define module_driver(__driver, __register, __unregister, ...) \
 2 static int __init __driver##_init(void) \
 3 { \
 4     return __register(&(__driver) , ##__VA_ARGS__); \
 5 } \
 6 module_init(__driver##_init); \
 7 static void __exit __driver##_exit(void) \
 8 { \
 9     __unregister(&(__driver) , ##__VA_ARGS__); \
10 } \
11 module_exit(__driver##_exit);

山重水复疑无路,柳暗花明又一村.这东东你让我说啥~没说的.相信大家也不想在听我唠叨.但是这里为什么多此一举写了这么一个叫宏,而不是像其他的linux模块那样直接写两个module_xxx呢?这是因为这个设备eeprom本身是不可插拔的,也就不需要什么加载卸载的过程,系统上电运行直接就注册了.
那么我们知道了,现在因为SPI子系统核心层我们已经注册了一条SPI总线,就是spi_bus_type.它里面的match回调函数我们已经看过了,就是spi_match_device.就是在这个函数中将完成这个spi_device和spi_driver的匹配,匹配成功就会去执行spi_driver的probe回调了.我们来看,at25_probe函数在drivers/msic/eeprom/at25.c中:

  1 static int at25_probe(struct spi_device *spi)
  2 {
  3     struct at25_data    *at25 = NULL;/*这个结构其实就是对spi_device的封装,我们可以像理解面向对象那样将这个结构理解为对spi_device的实例*/
  4     struct spi_eeprom    chip;/*此结构用来作为记录一个SPI EEPROMS的句柄,它保存了platform_data的数据*/
  5     struct device_node    *np = spi->dev.of_node;
  6     int            err;
  7     int            sr;
  8     int            addrlen;
  9 
 10     /* Chip description */
 11     if (!spi->dev.platform_data) {/*具体到dm365平台,此platform_data就是arch/arm/mach-davinci/board-ddm365-evm.c中定义的的at25640*/
 12         if (np) {
 13             err = at25_np_to_chip(&spi->dev, np, &chip);
 14             if (err)
 15                 goto fail;
 16         } else {
 17             dev_err(&spi->dev, "Error: no chip description\n");
 18             err = -ENODEV;
 19             goto fail;
 20         }
 21     } else
 22         chip = *(struct spi_eeprom *)spi->dev.platform_data;
 23 
 24     /* For now we only support 8/16/24 bit addressing */
 25     if (chip.flags & EE_ADDR1)/*flags用来标志eeprom的位宽和读写模式,具体到dm365平台此flags为EE_ADDR2*/
 26         addrlen = 1;
 27     else if (chip.flags & EE_ADDR2)
 28         addrlen = 2;
 29     else if (chip.flags & EE_ADDR3)
 30         addrlen = 3;
 31     else {
 32         dev_dbg(&spi->dev, "unsupported address type\n");
 33         err = -EINVAL;
 34         goto fail;
 35     }
 36 
 37     /* Ping the chip ... the status register is pretty portable,
 38      * unlike probing manufacturer IDs.  We do expect that system
 39      * firmware didn't write it in the past few milliseconds!
 40      */
 41     /*ping一下芯片,状态寄存器是很容易被检测的,不像制造商ID那样麻烦.我们期待系统固件之前没有写入它.*/
 42     sr = spi_w8r8(spi, AT25_RDSR);/*同步的读取状态寄存器的值,返回的八位数据保存在sr中.spi_w8r8这个函数有可能会睡眠*/
 43     if (sr < 0 || sr & AT25_SR_nRDY) {
 44         dev_dbg(&spi->dev, "rdsr --> %d (%02x)\n", sr, sr);
 45         err = -ENXIO;
 46         goto fail;
 47     }
 48 
 49     if (!(at25 = kzalloc(sizeof *at25, GFP_KERNEL))) {/*以kmalloc分配内存,并清0*/
 50         err = -ENOMEM;
 51         goto fail;
 52     }
 53 
 54     mutex_init(&at25->lock);/*初始化互斥体*/
 55     at25->chip = chip;/*记录下spi_eeprom*/
 56     at25->spi = spi_dev_get(spi);/*记录下这个片子对应的spi_device*/
 57     dev_set_drvdata(&spi->dev, at25);/*spi->dev.device_private->driver_data = at25*/
 58     at25->addrlen = addrlen;/*我觉得应该可以理解为这个片子使用的位宽是多少个字节.那根据上文分析,此处值为2*/
 59 
 60     /* Export the EEPROM bytes through sysfs, since that's convenient.
 61      * And maybe to other kernel code; it might hold a board's Ethernet
 62      * address, or board-specific calibration data generated on the
 63      * manufacturing floor.
 64      *
 65      * Default to root-only access to the data; EEPROMs often hold data
 66      * that's sensitive for read and/or write, like ethernet addresses,
 67      * security codes, board-specific manufacturing calibrations, etc.
 68      */
 69     /*通过sysfs文件系统导出EEPROM的字节,因为这是很方便的.也许其他内核代码也是这样做的:比如保存板子的以太网地址,或者是生产商的特定板的校验数据.
 70     默认只有root用户能够访问的数据.EEPROMs经常保存一些敏感的读或写的数据,像是以太网地址,安全码,特定板的校准数据等*/
 71     sysfs_bin_attr_init(&at25->bin);/*初始化一个动态分配的bin_attribute属性*/
 72     at25->bin.attr.name = "eeprom";/*属性的名字*/
 73     at25->bin.attr.mode = S_IRUSR;/*属性的模式(用户可读)*/
 74     at25->bin.read = at25_bin_read;/*属性的读方法*/
 75     at25->mem.read = at25_mem_read;/*片子的内存读函数*/
 76 
 77     at25->bin.size = at25->chip.byte_len;
 78     if (!(chip.flags & EE_READONLY)) {/*flags用来标志eeprom的位宽和读写模式,具体到dm365平台此flags为EE_ADDR2*/
 79         at25->bin.write = at25_bin_write;/*如果eeprom片子不是只读的话,那么就设置属性的写方法*/
 80         at25->bin.attr.mode |= S_IWUSR;/*增加属性的模式(用户可写)*/
 81         at25->mem.write = at25_mem_write;/*片子的内存写函数*/
 82     }
 83 
 84     err = sysfs_create_bin_file(&spi->dev.kobj, &at25->bin);/*创建一个二进制的属性文件*/
 85     if (err)
 86         goto fail;
 87 
 88     if (chip.setup)/*如果片子定义了setup函数,具体到dm365平台,此platform_data就是arch/arm/mach-davinci/board-ddm365-evm.c中定义的的at25640里并没有
 89     定义这个函数,因此为空*/
 90         chip.setup(&at25->mem, chip.context);/*使用片子的setup函数做一些初始化*/
 91 
 92     dev_info(&spi->dev, "%Zd %s %s eeprom%s, pagesize %u\n",
 93         (at25->bin.size < 1024)
 94             ? at25->bin.size
 95             : (at25->bin.size / 1024),
 96         (at25->bin.size < 1024) ? "Byte" : "KByte",
 97         at25->chip.name,
 98         (chip.flags & EE_READONLY) ? " (readonly)" : "",
 99         at25->chip.page_size);
100     return 0;
101 fail:
102     dev_dbg(&spi->dev, "probe err %d\n", err);
103     kfree(at25);
104     return err;
105 }

根据代码就能知道,这个spi_device实际上对应的是一个eeprom,而这里就是它的操作的一些初始化.也就是说,对于分析的这个davinci代码的实例,是dm365平台的,其开发板上应该是将eeprom通过spi总线挂接在了spi_master上.也就是挂接在了SOC上,因为我们的dm365片子本身就集成了spi_master.之后要访问eeprom其实回调最终的都是这里提供的一些接口.听起来有点黏糊,看个图吧:

哎,就写到这里,本人不会用visio,画个这图画了一下午~丢人啊!

posted on 2013-07-01 18:14 冷烟花阅读(12896) 评论(0) 编辑收藏举报