device tree 정리

DTS (Device Tree Source) file

arch/arm/boot/dts

.dts  : board-level definitions

.dtsi : SoC-level definitions 

device tree compiler

scripts/dts

device tree blob

produced by the compiler

passed by the bootloader and parseed at boot time

arch/arm/boot/dts/Makefile

lists which DTSs should be generated at build time

. bootloader의 일

bootload loads  (kernel image)

uImage

or

zImage

ATAGS 초기화

memory size, location 등의 정보를 지님

Linux command line 정보를 지님

kernel에게 

보드 정보 pass (via r1)

U-boot command

bootm <kernel img addr>

. device tree 이전

   ----------------------------

    | ATAGS   |    uImage   |

   ----------------------------

     r1 = <machine type>

     r2 = <pointer to ATAGS>

. device tree 이후

커널은 더이상 hardware description 정보를 지니지 않음

device tree blob이란 binary에 저장되어 있음

bootload는 다음의 2개를 load

1) uImage or zImage

2) DTB (located in arch/arm/boot/dts/) <- one per board

bootloader가 

DTB address를 r2로 전달

(memrory information으로 DTB가 조절될 수 있음)

U-boot command

bootm <kernel img addr> - <dtb addr>

    ----------------------------------

      | DTB |     | uImage          |

    ----------------------------------

r1 = don't care

r2 = pointer to DTB

. legacy device tree

CONFIG_ARM_APPENDED_DTB option

cat arch/arm/boot/zImage arch/arm/boot/dts/myboard.dtb > my-zImage

mkimage ... -d my-zImage my-uImage

CONFIG_ARM_ATAG_DTB_COMPAT 

커널이 ATAGS 정보를 읽고 DT를 update

. Device Tree Syntax

       +--- node name

       | +- unit address

       | |

/ {    v v

    node@0 {

        a-string-property = "A string";   <-- property name = value

        a-string-list-prop = "1" "2" "3";

        a-byte-data-prop = [0x01 0x02 0x03 0x04];

        child-node@0 {

            first-child-prop;

            second-child-prop = <1>;

            a-ref-to-something = <&node1>;    <- reference to another node

        };

        child-node@1 {

        };

    };

     +--- label

     |

     v

    node1: node@1 {

        an-empty-prop;

        a-cell-prop = <1 2 3 4>           <-- four cells (32 bits values)

        child-node@0 {

        };

    };

ex.

    auart0: serial@8006a000 {

           +--- id used by the OS

           |

           v

        compatible = "fsl,imx28-auart", "fsl,imx23-auart";

        reg = <0x8006a000 0x2000>;                          <- addr & length

        interrupts = <112>;                                 <- IRQ number

        dmas = <&dma_apbx 8>, <&dma_apbx 9>;                <- DMA engine and ch, with names

        dma-names = "rx", "tx";

        clocks = <&clks 45>                                 <- clk ref.

        status = "disabled";                                <- dev is not enabled

    };

static struct of_device_id mxs_ausrt_dt_ids[] = {

    {

        .compatible = "fsl,imx28-uart",

        .data = "mxs_auart_devtype[IMX28_AUART]

    }, 

    {

        .compatible = "fsl,imx23-uart",

        .data = "mxs_auart_devtype[IMX23_AUART]

    },

    {

        /* sentinel */

    }

};

MODULE_DEVICE_TABLE(of, mxs_auart_dt_ids);

[...]

static struct platform_driver mxs_auart_driver = {

    .probe = mxs_auart_probe,

    .remove = mxs_auart_remove,

    .driver = {

        .name = "mxs-auart",

        .of_match_table = mxs_auart_dt_ids,

    },

};

static int mxs_auart_probe(struct platform_device *pdev)

{

    const struct of_device_id *of_id = 

        of_match_device(mxs_auart_dt_ids, &pdev->dev);

    if (!of_id) {

        ....

        return....

    }

    /* use of_id->data here */

    s->clk = clk_get(&pdev->dev, NULL);

    // getting the I/O register resource

    r = platform_get_resource(pdev, IORESOURCE_MEM, 0);

    s->irq = platform_get_irq(pdev, 0);    // get IRQ nr

    s->rx_dma_chan = dma_request_slave_channel(s->dev, "rx");

    s->tx_dma_chan = dma_request_slave_channel(s->dev, "tx");

    // custom property

    struct device_node *np = pdev->dev.of_node;

    if (of_get_property(np, "fsl,uart-has-rtscts", NULL))

    ...

}

. device tree inclusion

여러 file로 구성 가능

.dtsi가 .dts file들을 includsion

보통

.dtsi가 SoC-level의 information을 contain

.dts file은 board-level information을 contain

. device tree binding

ref.

Documentation/devicetree/bindings

properties, values에 대한 명시

새로운 binding 추가 시, 

devicetree@vger.kernel.org에 post 하여 maintainer에 알려야 함

* Freescale MXS Application UART (AUART)

   Required properties:

    - compatible : Should be "fsl,<soc>-auart". The supported SoCs include

      imx23 and imx28.

    - reg : Address and length of the register set for the device

    - interrupts : Should contain the auart interrupt numbers

    - dmas: DMA specifier, consisting of a phandle to DMA controller node

      and AUART DMA channel ID.

      Refer to dma.txt and fsl-mxs-dma.txt for details.

    - dma-names: "rx" for RX channel, "tx" for TX channel.

    Example:

    auart0: serial@8006a000 {

        compatible = "fsl,imx28-auart", "fsl,imx23-auart";

        reg = <0x8006a000 0x2000>;

        interrupts = <112>;

        dmas = <&dma_apbx 8>, <&dma_apbx 9>;

        dma-names = "rx", "tx";

    };

    Note: Each auart port should have an alias correctly numbered in "aliases"

    node.

. device tree organization: top-level nodes

root 밑에는 보통, 

cpus ndoe

memory node

chosen node

aliases node

...

one or more nodes defining the buses in he SoC

one or more nodes defining on-board devices

    / {

        aliases { ... };

        cpus { ... };

        apb@80000000 {

            apbh@80000000 {

                /* Some devices */

            };

        apbx@80040000 {

            /* Some devices */

        };

    };

    ahb@80080000 {

        /* Some devices */

    };

};