• 一、 尝试在 spi 驱动里边读取 设备树里面 节点的信息

    //  dts  里面的参数配置503 &spi0 {504     status = "okay";505     pinctrl-name = "default";506     pinctrl-0 = <&spi0_pins>;507     ti,pindir-d0-out-d1-in;508509     wk2124A {510         compatible = "wk2124A";511         reg = <0>;512         name = "chenfulin";513         // spi-cpha = <1>;514         // spi-tx-bus-width = <1>;515         // spi-rx-bus-width = <1>;516         spi-max-frequency = <10000000>;517     };518 };

• 二、 代码跟踪

    //  drivers/spi/spi.c1428 #if defined(CONFIG_OF)1429 static struct spi_device *1430 of_register_spi_device(struct spi_master *master, struct device_node *nc)·1431 {// ... 1454     /* Device address */1455     rc = of_property_read_u32(nc, "reg", &value);           // 看他是怎么找到 reg 的值的1456     if (rc) {1457         dev_err(&master->dev, "%s has no valid 'reg' property (%d)\n",1458             nc->full_name, rc);1459         goto err_out;1460     }  //  include/linux/of.h 857 static inline int of_property_read_u32(const struct device_node *np,858                        const char *propname,859                        u32 *out_value)860 {861     return of_property_read_u32_array(np, propname, out_value, 1);        // 从函数可以看出，找的是一个 u32的值862 }// drivers/of/base.c 1252 int of_property_read_u32_array(const struct device_node *np,1253                    const char *propname, u32 *out_values,1254                    size_t sz)1255 {1256     const __be32 *val = of_find_property_value_of_size(np, propname,            // 然后函数又封了一层1257                         (sz * sizeof(*out_values)));12581259     if (IS_ERR(val))1260         return PTR_ERR(val);12611262     while (sz--)1263         *out_values++ = be32_to_cpup(val++);1264     return 0;1265 }1266 EXPORT_SYMBOL_GPL(of_property_read_u32_array);1125 static void *of_find_property_value_of_size(const struct device_node *np,1126             const char *propname, u32 len)1127 {1128     struct property *prop = of_find_property(np, propname, NULL);               // 这里就是找到节点的函数，这个 property 的链表就是设备树节点1129q1130     if (!prop)1131         return ERR_PTR(-EINVAL);1132     if (!prop->value)1133         return ERR_PTR(-ENODATA);1134     if (len > prop->length)1135         return ERR_PTR(-EOVERFLOW);11361137     return prop->value;1138 }232 struct property *of_find_property(const struct device_node *np,233                   const char *name,234                   int *lenp)235 {236     struct property *pp;237     unsigned long flags;238239     raw_spin_lock_irqsave(&devtree_lock, flags);240     pp = __of_find_property(np, name, lenp);            //  加一个自旋锁 保证安全，然后继续匹配241     raw_spin_unlock_irqrestore(&devtree_lock, flags);242243     return pp;244 }245 EXPORT_SYMBOL(of_find_property);213 static struct property *__of_find_property(const struct device_node *np,214                        const char *name, int *lenp)215 {216     struct property *pp;217218     if (!np)219         return NULL;220221     for (pp = np->properties; pp; pp = pp->next) {222         if (of_prop_cmp(pp->name, name) == 0) {             // 如果找到了就直接返回 pp节点。223             if (lenp)224                 *lenp = pp->length;225             break;226         }227     }228229     return pp;230 }include/linux/of.h227 #define of_prop_cmp(s1, s2)     strcmp((s1), (s2))

• 三、 关联起来的过程如下

    // driver/spi/spi.c1428 #if defined(CONFIG_OF)1429 static struct spi_device *1430 of_register_spi_device(struct spi_master *master, struct device_node *nc)1431 {1432     struct spi_device *spi;1433     int rc;1434     u32 value;// ... ..1521     /* Store a pointer to the node in the device structure */1522     of_node_get(nc);1523     spi->dev.of_node = nc;// ... ... 这里直接把设备节点挂在了 spi-dev.of_node 下面，  上面的 np 就是节点//  struct property *pp == pp = np->properties    np 是一个链表。1538 } 

• 四、在 spi drrver 里面找出相关参数

    //  probe 函数里面1521 #if 11522     printk("wk2124A debug speed : %d\n", spi->max_speed_hz);15231524     for (pp = spi->dev.of_node->properties; pp; pp = pp->next)1525     {1526         printk("%s   \n", pp->name);1527         if (strcmp(pp->name, "name") == 0)1528             printk("name : %s\n", (char *)pp->value);1529     }1530     printk("\n");1531 #endif