系列文章目录

Exynos4412 移植针对Samsung的Linux-6.1（一）下载、配置、编译Linux-6.1
Exynos4412 移植针对Samsung的Linux-6.1（二）SD卡驱动——解决无法挂载SD卡的根文件系统
Exynos4412 移植针对Samsung的Linux-6.1（三）SD卡驱动——解决mmc0: Timeout waiting for hardware interrupt.
Exynos4412 移植针对Samsung的Linux-6.1（四）NandFlash卡驱动
Exynos4412 移植针对Samsung的Linux-6.1（五）DM9000网卡驱动

Exynos4412 移植针对Samsung的Linux-6.1（二）SD卡驱动

系列文章目录
1、检查Linux内核的配置
2、修改设备树
3、解决无法挂载SD卡的根文件系统

Linux对于SD的支持是很全面的、很完善的。按道理来说，移植SD卡应该很简单。但是，我在移植SD卡驱动的时候，碰到了2个问题：

加载SDMMC驱动正常，但是无法发现SD卡
无法挂载SD卡上的根文件系统

解决以上问题仍然花费了很长时间解决问题。问题的解决，关键是对设备树的修改。现记录下来，供大家参考以避坑。

在这里插入图片描述
由电路图可以看出，SD卡用到了CLK、CMD、DATA和CD这4类引脚。WP引脚是写保护，电路上是接地的，根本就不起作用。我这次出问题，就出在CD这个引脚上。CD引脚是用来检测是否插入SD卡的，当SD卡插入时引脚电平会被拉低。
另外，开发板上是接到了SDMMC2控制器上。

1、检查Linux内核的配置

执行了make exynos_defconfig之后，默认是配置加载SDMMC驱动的。但是，还是检查一下为好。有2个地方，一是Device Drivers ；另一个是File systems,要想支持中文还得选上Simplified Chinese charset 。

Device Drivers —>
       <*> MMC/SD/SDIO card support —>
              < > ARM AMBA Multimedia Card Interface support
              <*> Secure Digital Host Controller Interface support
                     < > SDHCI platform and OF driver helper
                    <*> SDHCI support on Samsung S3C/S5P/Exynos SoC
              [*] DMA support on S3C SDHCI
              < > MMC/SD/SDIO over SPI
              <*> Synopsys DesignWare Memory Card Interface
File systems —>
       [ ] Validate filesystem parameter description
       <*> Second extended fs support
       [ ] Ext2 extended attributes
       < > The Extended 3 (ext3) filesystem
       <*> The Extended 4 (ext4) filesystem
       -*- Native language support —>
              <*> Simplified Chinese charset (CP936, GB2312)
              <*> NLS UTF-8

2、修改设备树

SDMMC设备树的写法，根据开发板的不同，有不同的写法。

例1：来自基于tiny4412的Linux内核移植 – SD卡驱动移植（五）。这篇博文中，目标板是tiny4412，作者碰到了问题：

[    2.245838] s3c-sdhci 12530000.sdhci: No vmmc regulator found
[    2.251358] s3c-sdhci 12530000.sdhci: No vqmmc regulator found

原因是设备树中没有为sdhc2设置vmmc或者vqmmc。这两个是关于regulator的。该作者采用的设备树如下：

        regulators {compatible = "simple-bus";#address-cells = <1>;#size-cells = <0>;mmc_reg: regulator@0 {compatible = "regulator-fixed";reg = <0>;regulator-name = "VMEM_VDD_2.8V";regulator-min-microvolt = <2800000>;regulator-max-microvolt = <2800000>;enable-active-high;};};&sdhci_2 {bus-width = <4>;pinctrl-0 = <&sd2_clk &sd2_cmd &sd2_cd &sd2_bus4>;pinctrl-names = "default";vmmc-supply = <&mmc_reg>;			status = "okay";//status = "disabled";
};

regulator与电源管理有关。但是，我的开发板上没有电源管理芯片，所以这样的写法复制到我的dts文件中，会语法错误，编译不通过。

例2：Documentation/devicetree/bindings/mmc/samsung,s3c6410-sdhci.yaml
帮助文档的示例如下：

 66     #include <dt-bindings/clock/exynos4.h>67     #include <dt-bindings/gpio/gpio.h>68     #include <dt-bindings/interrupt-controller/arm-gic.h>69 70     mmc@12510000 {71         compatible = "samsung,exynos4210-sdhci";72         reg = <0x12510000 0x100>;73         interrupts = <GIC_SPI 73 IRQ_TYPE_LEVEL_HIGH>;74         clocks = <&clock CLK_SDMMC0>, <&clock CLK_SCLK_MMC0>;75         clock-names = "hsmmc", "mmc_busclk.2";76         bus-width = <4>;77         cd-gpios = <&gpx3 4 GPIO_ACTIVE_LOW>;78         pinctrl-0 = <&sd2_clk &sd2_cmd &sd2_bus4 &sdhci2_cd>;79         pinctrl-names = "default";80         vmmc-supply = <&ldo21_reg>;81     };

以上第70 ~ 75行，在arch/arm/boot/dts/exynos4.dtsi中已经有了，只需要引用exynos4.dtsi就可以。可以看出，例子中添加了第77~80行的属性。
我按照上述属性修改我的设备树，如下：

 77 /* SD card deviceTree node78  * sdhci_2: sdhci@1253000079 */80 &sdhci_2 {81     pinctrl-0 = <&sd2_clk &sd2_cmd &sd2_bus4 &sd2_cd>;82     pinctrl-names = "default";83     samsung,bus-width = <4>;84     samsung,timing = <1 2 3>;85     cd-gpios = <&gpk2 2 0>;86     wp-gpios = <&gpx0 5 0>;87     status = "okay";88 };

虽然dts编译通过了，但是Linux启动时，显示加载了驱动，但是没有找到SD卡。

[    2.277294][    T9] of_get_named_gpiod_flags: parsed 'cd-gpios' property of node '/soc/mmc@12530000[0]' - status (0)
[    2.294318][    T9] s3c-sdhci 12530000.mmc: clock source 2: mmc_busclk.2 (20000000 Hz)
[    2.308484][    T9] s3c-sdhci 12530000.mmc: GPIO lookup for consumer cd
[    2.319385][    T9] s3c-sdhci 12530000.mmc: using device tree for GPIO lookup
[    2.326584][    T9] of_get_named_gpiod_flags: parsed 'cd-gpios' property of node '/soc/mmc@12530000[0]' - status (0)
[    2.342686][    T9] gpio_stub_drv gpiochip15: Persistence not supported for GPIO 2
[    2.354581][    T9] s3c-sdhci 12530000.mmc: Got CD GPIO
[    2.364380][    T9] s3c-sdhci 12530000.mmc: GPIO lookup for consumer wp
[    2.377609][    T9] s3c-sdhci 12530000.mmc: using device tree for GPIO lookup
[    2.390432][    T9] of_get_named_gpiod_flags: parsed 'wp-gpios' property of node '/soc/mmc@12530000[0]' - status (0)
[    2.400806][    T9] gpio_stub_drv gpiochip32: Persistence not supported for GPIO 5
[    2.416815][    T9] s3c-sdhci 12530000.mmc: Got WP GPIO
[    2.466252][    T9] mmc0: SDHCI controller on samsung-hsmmc [12530000.mmc] using ADMA

其中，有2行错误

[    2.342686][    T9] gpio_stub_drv gpiochip15: Persistence not supported for GPIO 2
[    2.400806][    T9] gpio_stub_drv gpiochip32: Persistence not supported for GPIO 5

第一行针对cd-gpios = <&gpk2 2 0>;，第二行针对wp-gpios = <&gpx0 5 0>;。查找Linux-6.1的源码，Persistence not supported代表的含义是pin的状态是睡眠或者控制器重置。

@PIN_CONFIG_PERSIST_STATE: retain pin state across sleep or controller reset

后来，我受到启发，想到可能是cd-gpios的属性设置不正确，于是把第85行cd-gpios属性注释掉，问题就解决了。CBT4412开发板的可行SDMMC设备树如下：

 77 /* SD card deviceTree node78  * sdhci_2: sdhci@1253000079 */80 &sdhci_2 {81     pinctrl-0 = <&sd2_clk &sd2_cmd &sd2_bus4 &sd2_cd>;82     pinctrl-names = "default";83     samsung,bus-width = <4>;84     samsung,timing = <1 2 3>;85     //  cd-gpios = <&gpk2 2 0>;86     wp-gpios = <&gpx0 5 0>;87     status = "okay";88 };

Linux启动结果：

[    2.465081][    T9] mmc0: SDHCI controller on samsung-hsmmc [12530000.mmc] using ADMA[    2.700852][   T35] mmc0: new high speed SD card at address 0002
[    2.732352][   T35] mmcblk0: mmc0:0002       968 MiB 
[    2.732992][    T1] /dev/root: Can't open blockdev
[    2.739237][    T1] VFS: Cannot open root device "mmcblk0p3" or unknown-block(0,0): error -6
[    2.742335][   T35]  mmcblk0: p1 p2 p3
[    2.880395][    T1]  driver: mmcblk
[    2.888522][    T1]   b301           10240 mmcblk0p1 c5a42637-01
[    2.888534][    T1] 
[    2.896680][    T1]   b302          614400 mmcblk0p2 c5a42637-02
[    2.896691][    T1] 
[    2.904839][    T1]   b303          363008 mmcblk0p3 c5a42637-03
[    2.904850][    T1] 
[    2.913065][    T1] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

3、解决无法挂载SD卡的根文件系统

此时，无法完全启动Linux，显示无法挂载SD卡上的根文件系统

Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

原因是挂载根文件系统太早了，此时SD卡还没有挂载完成。
解决方法也很简单，修改BootLoader的启动参数，增加rootwait就可以。如下：

setenv bootargs root=/dev/mmcblk0p3  rw rootfstype=ext4 init=/linuxrc console=ttySAC0,115200n8 rootwait

启动结果如下：

[    2.699872][   T35] mmc0: new high speed SD card at address 0002
[    2.729229][    T1] Waiting for root device /dev/mmcblk0p3...
[    2.730965][   T35] mmcblk0: mmc0:0002       968 MiB 
[    2.746932][   T35]  mmcblk0: p1 p2 p3
[    3.311368][    T1] EXT4-fs (mmcblk0p3): recovery complete
[    3.314494][    T1] EXT4-fs (mmcblk0p3): mounted filesystem with ordered data mode. Quota mode: disabled.
[    3.314748][    T1] VFS: Mounted root (ext4 filesystem) on device 179:3.
[    3.316175][    T1] devtmpfs: mounted
[    3.317624][    T1] Freeing unused kernel image (initmem) memory: 1024K
[    3.321581][    T1] Run /linuxrc as init process
[    3.325766][    T1]   with arguments:
[    3.329340][    T1]     /linuxrc
[    3.332590][    T1]   with environment:
[    3.336371][    T1]     HOME=/
[    3.339408][    T1]     TERM=linux
can't run '/etc/init.d/rcS': No such file or directoryPlease press Enter to activate this console. 
/ # ls
bin         etc.old     linuxrc     proc        tmp
dev         home        mk_mod_.sh  sbin        usr
etc         lib         mnt         sys         var
/ #