• 最近做了一個 spi 設備驅動從板級設備驅動升級到設備樹設備驅動，這其中要了解 spi 設備樹代碼的解析。

• 設備樹配置如下：

  503 &spi0 {
  504     status = "okay";
  505     pinctrl-name = "default";
  506     pinctrl-0 = <&spi0_pins>;
  507     ti,pindir-d0-out-d1-in;
  508
  509     wk2124A {
  510         compatible = "wk2124A";    //  匹配字符串
   
  
  511         reg = <0>;                    // cs 
  512         # spi-cpha = <1>;              // 配置 spi  的模式
  513         # spi-tx-bus-width = <1>;   // 這是是 spi-tx 的總線寬度
  514         # spi-rx-bus-width = <1>;
  515         spi-max-frequency = <10000000>;        // spi 最大速率配置
  516     };
  517 };
   
  

• 代碼跟蹤

  // drivers/spi/spi.c
  2772 postcore_initcall(spi_init);
  
  2733 static int __init spi_init(void)
  2734 {
  2735     int status;
  2736
  2737     buf = kmalloc(SPI_BUFSIZ, GFP_KERNEL);
  2738     if (!buf) {
  2739         status = -ENOMEM;
  2740         goto err0;
  2741     }
  2742
  2743     status = bus_register(&spi_bus_type);
  2744
   
       if (status < 0)
  2745         goto err1;
  2746
  2747     status = class_register(&spi_master_class);
  2748     if (status < 0)
  2749         goto err2;
  2750
  2751     if (IS_ENABLED(CONFIG_OF_DYNAMIC))
  2752         WARN_ON(of_reconfig_notifier_register(&spi_of_notifier));
  2753
  2754     return 0;
  2755
  2756 err2:
  2757     bus_unregister(&spi_bus_type);
  2758 err1:
  2759     kfree(buf);
  2760     buf = NULL;
  2761 err0:
  2762     return status;
  2763 }
  
  2726 static struct notifier_block spi_of_notifier = {
  2727     .notifier_call = of_spi_notify,
  2728 };
  
  2686 static int of_spi_notify(struct notifier_block *nb, unsigned long action,
  2687              void *arg)
  2688 {
  2689     struct of_reconfig_data *rd = arg;
  2690     struct spi_master *master;
  2691     struct spi_device *spi;
  2692
  2693     switch (of_reconfig_get_state_change(action, arg)) {
  2694     case OF_RECONFIG_CHANGE_ADD:
  2695         master = of_find_spi_master_by_node(rd->dn->parent);
  2696         if (master == NULL)
  2697             return NOTIFY_OK;   /* not for us */
  2698
  2699         spi = of_register_spi_device(master, rd->dn);   // ---> 註冊設備
  2700         put_device(&master->dev);
                  // ... ... 
  2722
  2723     return NOTIFY_OK;
  2724 }
  
  1428 #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;
  1435
  1436     /* Alloc an spi_device */
  1437     spi = spi_alloc_device(master);
  1438     if (!spi) {
  1439         dev_err(&master->dev, "spi_device alloc error for %s\n",
  1440             nc->full_name);
  1441         rc = -ENOMEM;
  1442         goto err_out;
  1443     }
  1444
  1445     /* Select device driver */
  1446     rc = of_modalias_node(nc, spi->modalias,
  1447                 sizeof(spi->modalias));
  1448     if (rc < 0) {
  1449         dev_err(&master->dev, "cannot find modalias for %s\n",
  1450             nc->full_name);
  1451         goto err_out;
  1452     }
  1453
  1454     /* Device address */
  1455     rc = of_property_read_u32(nc, "reg", &value);
  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     }
  1461     spi->chip_select = value;
  1462
  1463     /* Mode (clock phase/polarity/etc.) */
  1464     if (of_find_property(nc, "spi-cpha", NULL))
  1465         spi->mode |= SPI_CPHA;
  1466     if (of_find_property(nc, "spi-cpol", NULL))
  1467         spi->mode |= SPI_CPOL;
  1468     if (of_find_property(nc, "spi-cs-high", NULL))
  1469         spi->mode |= SPI_CS_HIGH;
  1470     if (of_find_property(nc, "spi-3wire", NULL))
  1471         spi->mode |= SPI_3WIRE;
  1472     if (of_find_property(nc, "spi-lsb-first", NULL))
  1473         spi->mode |= SPI_LSB_FIRST;
  1474
  1475     /* Device DUAL/QUAD mode */
  1476     if (!of_property_read_u32(nc, "spi-tx-bus-width", &value)) {
  1477         switch (value) {
  1478         case 1:
  1479             break;
  1480         case 2:
  1481             spi->mode |= SPI_TX_DUAL;
  1482             break;
  1483         case 4:
  1484             spi->mode |= SPI_TX_QUAD;
  1485             break;
  1486         default:
  1487             dev_warn(&master->dev,
  1488                 "spi-tx-bus-width %d not supported\n",
  1489                 value);
  1490             break;
  1491         }
  1492     }
  1493
  1494     if (!of_property_read_u32(nc, "spi-rx-bus-width", &value)) {
  1495         switch (value) {
  1496         case 1:
  1497             break;
  1498         case 2:
  1499             spi->mode |= SPI_RX_DUAL;
  1500             break;
  1501         case 4:
  1502             spi->mode |= SPI_RX_QUAD;
  1503             break;
  1504         default:
  1505             dev_warn(&master->dev,
  1506                 "spi-rx-bus-width %d not supported\n",
  1507                 value);
  1508             break;
  1509         }
  1510     }
  1511
  1512     /* Device speed */
  1513     rc = of_property_read_u32(nc, "spi-max-frequency", &value);
  1514     if (rc) {
  1515         dev_err(&master->dev, "%s has no valid 'spi-max-frequency' property      (%d)\n",
  1516             nc->full_name, rc);
  1517         goto err_out;
  1518     }
  1519     spi->max_speed_hz = value;
  1520
  1521     /* Store a pointer to the node in the device structure */
  1522     of_node_get(nc);
  1523     spi->dev.of_node = nc;
  1524
  1525     /* Register the new device */
  1526     rc = spi_add_device(spi);
  1527     if (rc) {
  1528         dev_err(&master->dev, "spi_device register error %s\n",
  1529             nc->full_name);
  1530         goto err_out;
  1531     }
  1532
  1533     return spi;
  1534
  1535 err_out:
  1536     spi_dev_put(spi);
  1537     return ERR_PTR(rc);
  1538 }    

Linux kernel 有關 spi 設備樹參數解析