Architecture

The SDIO host driver follows Linux MMC subsystem. The architecture is shown in following figure.

../../_images/mmc_arch.svg — MMC architecture

The MMC framework is divided into 3 layers: MMC host driver, MMC core and MMC card driver. The MMC card driver registers the MMC subsystem as a block device, and the upper layer can access MMC subsystem through the block device with file system.

The MMC core implements the core logic of bus and MMC/SD/SDIO protocols. MMC host driver is implemented to connect host controller with MMC core, and SDIO driver is implemented on this layer.

Implementation

The SDIO host driver is implemented as following files:

Driver location	Introduction
<linux>/drivers/rtkdrivers/mmc/Kconfig	SDIO host driver Kconfig
<linux>/drivers/rtkdrivers/mmc/Makefile	SDIO host driver Makefile
<linux>/drivers/rtkdrivers/mmc/rtk-mmc.c	SDIO host driver.
<linux>/drivers/rtkdrivers/mmc/rtk-mmc.h	SDIO host driver head file.

Configuration

DTS Configuration

The DTS node is defined in <dts>/rtl8730e-ocp.dtsi.

sdioh: sdioh@400D0000 {
   compatible = "realtek,ameba-sdiohost";
   reg = <0x400D0000 0x8000>;
   interrupts = <GIC_SPI 38 IRQ_TYPE_LEVEL_HIGH>;
   clocks = <&rcc RTK_CKE_SDH>;
   status = "okay";
};

The following table is property description:

Property	Description	Configurable?
compatible	ID to match the driver and device	No
reg	Register resource	No
interrupts	SPI interrupt	No
clocks	SDIO clock node	No
status	SDIOH inyrttupt status	No

DTS nodes of pinctrl are defined in <dts>/rtl8730e-pinctrl.dtsi.

sdioh_pins: sdioh@0 {
   pins {
      pinmux = <REALTEK_PINMUX('B', 27, SDIO)>, // SD_CMD
               <REALTEK_PINMUX('B', 28, SDIO)>, // SD_CLK
               <REALTEK_PINMUX('C', 0, SDIO)>, // SD_CD
               <REALTEK_PINMUX('B', 29, SDIO)>, // SD_D0
               <REALTEK_PINMUX('B', 25, SDIO)>, // SD_D1
               <REALTEK_PINMUX('B', 26, SDIO)>, // SD_D2
               <REALTEK_PINMUX('B', 30, SDIO)>; // SD_D3
               bias-pull-up;
               slew-rate = <0>;
               drive-strength = <0>;
   };
};

The following table is pinmux description:

Property	Description	Configurable?
pinmux	Pin definition of SDIO host	Yes
bias-pull-up	Pin pull status	Yes
slew-rate	Pin voltage slew rate	No
drive-strength	Pin drive strength	No

备注

Configure the pin according to the actual condition. If using 1-bit mode, SD_D1, SD_D2, SD_D3 can be annotated. If card detect and card protect function are not used, SD_CD, SD_WP can be annotated.

Build Configuration

Select Device Drivers > Drivers for Realtek > SDIO host driver:

APIs

APIs for User Space

The MMC subsystem provides user space interfaces:

dev/mmcblk0
dev/mmcblk0p1

User should mount the interface to a directory so that SDIO device can be accessed directly through the directory.

备注

Interfaces could be changed according to the actual conditions.

Take SD card as example. Once SD card plug into cable, MMC subsystem will response soon and create 2 device node – /dev/mmcblk0 and /dev/mmcblk0p1. User should mount it to file system if system does not do this automatically.

Mount SD card to file system:
```
mount /dev/mmcblk0pN /mnt/sdcard
```
Locate to SD card directory:
```
cd /mnt/sdcard
```
Create a directory in SD card:
```
mkdir  test_dir
```
Create a file in SD card directory test_dir:
```
touch test.txt
```
Write contents to the file test.txt
```
echo helloworld > test.txt
```
Read the file test.txt
```
cat test.txt
```

Refer to demo code to get more details. SDIO host demo is located at <test>/sdioh.

APIs for Kernel Space

None.