* Exynos DWC_mobile_storage

The Exynos provides DWC_mobile_storage interface which supports
. Embedded Multimedia Cards (EMMC-version 4.5)
. Secure Digital memory (SD mem-version 2.0)
. Secure Digital I/O (SDIO-version 3.0)
. Consumer Electronics Advanced Transport Architecture (CE-ATA-version 1.1)

The Exynos DWC_mobile_storage provides four channels.
SOC specific and Board specific properties are channel specific.

Required SoC Specific Properties:

- compatible: should be
	- samsung,exynos4412-dw-mshc: for Exynos4 platforms
	- samsung,exynos-dwmmc: for Exynos5 platforms
	- samsung,exynos7-dw-mshc-smu: for Exynos7 platforms (with SMU block)

- reg: physical base address of the controller and length of memory mapped
	region.

- interrupts: The interrupt number to the cpu.

Required Board Specific Properties:

- #address-cells: should be 1.
- #size-cells: should be 0.
- bus-width: The width of the bus used to interface the devices
	supported by DWC_mobile_storage (SD-MMC/EMMC/SDIO).
	. Typically the bus width is 4 or 8.
- samsung,dw-mshc-ciu-div: The divider value for the card interface unit (ciu)
	clock (0..7).
- samsung,dw-mshc-sdr-timing: The timing values for single data rate (SDR) mode
	operation.
	. First value is CIU clock phase shift value for TX mode (0..7).
	. Second value is CIU clock phase shift value for RX mode (0..7).
- samsung,dw-mshc-ddr-timing: The timing values for double data rate (DDR) mode
	operation. If missing, values from samsung,dw-mshc-sdr-timing are used.
	. First value is CIU clock phase shift value for TX mode (0..7).
	. Second value is CIU clock phase shift value for RX mode (0..7).

Example:

mmc@12200000 {
	bus-width = <8>;
	non-removable;
	samsung,dw-mshc-ciu-div = <3>;
	samsung,dw-mshc-sdr-timing = <1 3>;
	samsung,dw-mshc-ddr-timing = <0 2>;
};

In the above example,
	. The bus width is 8
	. Divider value for CLKSEL register is 3. The CIU clock rate will be
	  calculated as SDCLKIN / (3 + 1).
	. SDR and DDR timings are comprised of 2 values as explained below
		1 - SelClk_sample
		3 - SelClk_drv
	. The 'non-removable' flag indicates whether the particular device
	  cannot be removed (always present) or it is a removable device.
		Flag is present - Indicates that the device cannot be removed.
		Flag is not present - Indicates that the device is removable.
