linux/Documentation/devicetree/bindings/mmc/mmc.txt
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   1These properties are common to multiple MMC host controllers. Any host
   2that requires the respective functionality should implement them using
   3these definitions.
   4
   5Interpreted by the OF core:
   6- reg: Registers location and length.
   7- interrupts: Interrupts used by the MMC controller.
   8
   9Card detection:
  10If no property below is supplied, host native card detect is used.
  11Only one of the properties in this section should be supplied:
  12  - broken-cd: There is no card detection available; polling must be used.
  13  - cd-gpios: Specify GPIOs for card detection, see gpio binding
  14  - non-removable: non-removable slot (like eMMC); assume always present.
  15
  16Optional properties:
  17- bus-width: Number of data lines, can be <1>, <4>, or <8>.  The default
  18  will be <1> if the property is absent.
  19- wp-gpios: Specify GPIOs for write protection, see gpio binding
  20- cd-inverted: when present, polarity on the CD line is inverted. See the note
  21  below for the case, when a GPIO is used for the CD line
  22- wp-inverted: when present, polarity on the WP line is inverted. See the note
  23  below for the case, when a GPIO is used for the WP line
  24- max-frequency: maximum operating clock frequency
  25- no-1-8-v: when present, denotes that 1.8v card voltage is not supported on
  26  this system, even if the controller claims it is.
  27- cap-sd-highspeed: SD high-speed timing is supported
  28- cap-mmc-highspeed: MMC high-speed timing is supported
  29- cap-power-off-card: powering off the card is safe
  30- cap-sdio-irq: enable SDIO IRQ signalling on this interface
  31
  32*NOTE* on CD and WP polarity. To use common for all SD/MMC host controllers line
  33polarity properties, we have to fix the meaning of the "normal" and "inverted"
  34line levels. We choose to follow the SDHCI standard, which specifies both those
  35lines as "active low." Therefore, using the "cd-inverted" property means, that
  36the CD line is active high, i.e. it is high, when a card is inserted. Similar
  37logic applies to the "wp-inverted" property.
  38
  39CD and WP lines can be implemented on the hardware in one of two ways: as GPIOs,
  40specified in cd-gpios and wp-gpios properties, or as dedicated pins. Polarity of
  41dedicated pins can be specified, using *-inverted properties. GPIO polarity can
  42also be specified using the OF_GPIO_ACTIVE_LOW flag. This creates an ambiguity
  43in the latter case. We choose to use the XOR logic for GPIO CD and WP lines.
  44This means, the two properties are "superimposed," for example leaving the
  45OF_GPIO_ACTIVE_LOW flag clear and specifying the respective *-inverted
  46property results in a double-inversion and actually means the "normal" line
  47polarity is in effect.
  48
  49Optional SDIO properties:
  50- keep-power-in-suspend: Preserves card power during a suspend/resume cycle
  51- enable-sdio-wakeup: Enables wake up of host system on SDIO IRQ assertion
  52
  53Example:
  54
  55sdhci@ab000000 {
  56        compatible = "sdhci";
  57        reg = <0xab000000 0x200>;
  58        interrupts = <23>;
  59        bus-width = <4>;
  60        cd-gpios = <&gpio 69 0>;
  61        cd-inverted;
  62        wp-gpios = <&gpio 70 0>;
  63        max-frequency = <50000000>;
  64        keep-power-in-suspend;
  65        enable-sdio-wakeup;
  66}
  67