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Diffstat (limited to 'Documentation/devicetree/bindings/mmc/mmc.txt')
| -rw-r--r-- | Documentation/devicetree/bindings/mmc/mmc.txt | 34 |
1 files changed, 28 insertions, 6 deletions
diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt b/Documentation/devicetree/bindings/mmc/mmc.txt index a591c6741d75..85aada2263d5 100644 --- a/Documentation/devicetree/bindings/mmc/mmc.txt +++ b/Documentation/devicetree/bindings/mmc/mmc.txt @@ -6,23 +6,45 @@ Interpreted by the OF core: - reg: Registers location and length. - interrupts: Interrupts used by the MMC controller. -Required properties: -- bus-width: Number of data lines, can be <1>, <4>, or <8> - Card detection: -If no property below is supplied, standard SDHCI card detect is used. +If no property below is supplied, host native card detect is used. Only one of the properties in this section should be supplied: - broken-cd: There is no card detection available; polling must be used. - cd-gpios: Specify GPIOs for card detection, see gpio binding - non-removable: non-removable slot (like eMMC); assume always present. Optional properties: +- bus-width: Number of data lines, can be <1>, <4>, or <8>. The default + will be <1> if the property is absent. - wp-gpios: Specify GPIOs for write protection, see gpio binding -- cd-inverted: when present, polarity on the cd gpio line is inverted -- wp-inverted: when present, polarity on the wp gpio line is inverted +- cd-inverted: when present, polarity on the CD line is inverted. See the note + below for the case, when a GPIO is used for the CD line +- wp-inverted: when present, polarity on the WP line is inverted. See the note + below for the case, when a GPIO is used for the WP line - max-frequency: maximum operating clock frequency - no-1-8-v: when present, denotes that 1.8v card voltage is not supported on this system, even if the controller claims it is. +- cap-sd-highspeed: SD high-speed timing is supported +- cap-mmc-highspeed: MMC high-speed timing is supported +- cap-power-off-card: powering off the card is safe +- cap-sdio-irq: enable SDIO IRQ signalling on this interface + +*NOTE* on CD and WP polarity. To use common for all SD/MMC host controllers line +polarity properties, we have to fix the meaning of the "normal" and "inverted" +line levels. We choose to follow the SDHCI standard, which specifies both those +lines as "active low." Therefore, using the "cd-inverted" property means, that +the CD line is active high, i.e. it is high, when a card is inserted. Similar +logic applies to the "wp-inverted" property. + +CD and WP lines can be implemented on the hardware in one of two ways: as GPIOs, +specified in cd-gpios and wp-gpios properties, or as dedicated pins. Polarity of +dedicated pins can be specified, using *-inverted properties. GPIO polarity can +also be specified using the OF_GPIO_ACTIVE_LOW flag. This creates an ambiguity +in the latter case. We choose to use the XOR logic for GPIO CD and WP lines. +This means, the two properties are "superimposed," for example leaving the +OF_GPIO_ACTIVE_LOW flag clear and specifying the respective *-inverted +property results in a double-inversion and actually means the "normal" line +polarity is in effect. Optional SDIO properties: - keep-power-in-suspend: Preserves card power during a suspend/resume cycle |