1Rockchip SRAM for IO Voltage Domains:
2-------------------------------------
3
4IO domain voltages on some Rockchip SoCs are variable but need to be
5kept in sync between the regulators and the SoC using a special
6register.
7
8A specific example using rk3288:
9- If the regulator hooked up to a pin like SDMMC0_VDD is 3.3V then
10  bit 7 of GRF_IO_VSEL needs to be 0.  If the regulator hooked up to
11  that same pin is 1.8V then bit 7 of GRF_IO_VSEL needs to be 1.
12
13Said another way, this driver simply handles keeping bits in the SoC's
14general register file (GRF) in sync with the actual value of a voltage
15hooked up to the pins.
16
17Note that this driver specifically doesn't include:
18- any logic for deciding what voltage we should set regulators to
19- any logic for deciding whether regulators (or internal SoC blocks)
20  should have power or not have power
21
22If there were some other software that had the smarts of making
23decisions about regulators, it would work in conjunction with this
24driver.  When that other software adjusted a regulator's voltage then
25this driver would handle telling the SoC about it.  A good example is
26vqmmc for SD.  In that case the dw_mmc driver simply is told about a
27regulator.  It changes the regulator between 3.3V and 1.8V at the
28right time.  This driver notices the change and makes sure that the
29SoC is on the same page.
30
31
32Required properties:
33- compatible: should be one of:
34  - "rockchip,rk3188-io-voltage-domain" for rk3188
35  - "rockchip,rk3288-io-voltage-domain" for rk3288
36- rockchip,grf: phandle to the syscon managing the "general register files"
37
38
39You specify supplies using the standard regulator bindings by including
40a phandle the relevant regulator.  All specified supplies must be able
41to report their voltage.  The IO Voltage Domain for any non-specified
42supplies will be not be touched.
43
44Possible supplies for rk3188:
45- ap0-supply:    The supply connected to AP0_VCC.
46- ap1-supply:    The supply connected to AP1_VCC.
47- cif-supply:    The supply connected to CIF_VCC.
48- flash-supply:  The supply connected to FLASH_VCC.
49- lcdc0-supply:  The supply connected to LCD0_VCC.
50- lcdc1-supply:  The supply connected to LCD1_VCC.
51- vccio0-supply: The supply connected to VCCIO0.
52- vccio1-supply: The supply connected to VCCIO1.
53                 Sometimes also labeled VCCIO1 and VCCIO2.
54
55Possible supplies for rk3288:
56- audio-supply:  The supply connected to APIO4_VDD.
57- bb-supply:     The supply connected to APIO5_VDD.
58- dvp-supply:    The supply connected to DVPIO_VDD.
59- flash0-supply: The supply connected to FLASH0_VDD.  Typically for eMMC
60- flash1-supply: The supply connected to FLASH1_VDD.  Also known as SDIO1.
61- gpio30-supply: The supply connected to APIO1_VDD.
62- gpio1830       The supply connected to APIO2_VDD.
63- lcdc-supply:   The supply connected to LCDC_VDD.
64- sdcard-supply: The supply connected to SDMMC0_VDD.
65- wifi-supply:   The supply connected to APIO3_VDD.  Also known as SDIO0.
66
67
68Example:
69
70	io-domains {
71		compatible = "rockchip,rk3288-io-voltage-domain";
72		rockchip,grf = <&grf>;
73
74		audio-supply = <&vcc18_codec>;
75		bb-supply = <&vcc33_io>;
76		dvp-supply = <&vcc_18>;
77		flash0-supply = <&vcc18_flashio>;
78		gpio1830-supply = <&vcc33_io>;
79		gpio30-supply = <&vcc33_pmuio>;
80		lcdc-supply = <&vcc33_lcd>;
81		sdcard-supply = <&vccio_sd>;
82		wifi-supply = <&vcc18_wl>;
83	};
84