diff options
Diffstat (limited to 'Documentation/devicetree/bindings/mmc/cavium-mmc.txt')
| -rw-r--r-- | Documentation/devicetree/bindings/mmc/cavium-mmc.txt | 58 |
1 files changed, 50 insertions, 8 deletions
diff --git a/Documentation/devicetree/bindings/mmc/cavium-mmc.txt b/Documentation/devicetree/bindings/mmc/cavium-mmc.txt index 1433e6201dff..21ed6d4fedcc 100644 --- a/Documentation/devicetree/bindings/mmc/cavium-mmc.txt +++ b/Documentation/devicetree/bindings/mmc/cavium-mmc.txt @@ -17,16 +17,56 @@ Required properties: - clocks : phandle Optional properties: - - for cd, bus-width and additional generic mmc parameters - please refer to mmc.txt within this directory + - for cd, bus-width, vmmc-supply, vqmmc-supply, and additional generic + mmc parameters please refer to mmc.txt within this directory - cavium,cmd-clk-skew : number of coprocessor clocks before sampling command - cavium,dat-clk-skew : number of coprocessor clocks before sampling data Deprecated properties: -- spi-max-frequency : use max-frequency instead -- cavium,bus-max-width : use bus-width instead -- power-gpios : use vmmc-supply instead -- cavium,octeon-6130-mmc-slot : use mmc-slot instead + - spi-max-frequency : use max-frequency instead + - cavium,bus-max-width : use bus-width instead + - power-gpios : use vmmc-supply instead + - cavium,octeon-6130-mmc-slot : use mmc-slot instead + +GPIO control via vmmc-supply & vqmmc-supply: + Two types of regulator object can be specified as mmc properties, + typically regulator-fixed controlled by GPIO pins. + + Octeon/OcteonTX chips commonly use GPIO8 as an MMC-reset pin. + In systems which may boot from MMC, it starts as input, and is gently + pulled up/down by board logic to indicate the active sense of the + signal. Chip reset then drives the signal in the opposite direction + to effect a reset of target devices. + Device tree should model this with a vmmc-supply regulator, gated by + GPIO8, so GPIO8 is driven in the non-reset direction when MMC devices + are probed, and held there until rmmod/shutdown/suspend. + This allows a warm reboot to reset the MMC devices. + + Octeon/OcteonTX MMC supports up to 3 mmc slots, but any + level-shifting to accommodate different signal voltages is + done by external hardware, under control of an optional + vqmmc regulator object, typically controlled by GPIO. + + If any mmc-slots have a vqmmc-supply property, it is taken as a warning + that we must switch carefully between slots (unless they have the same + vqmmc object), tri-stating MMC signals to avoid any transient states + as level-shifters are enabled/disabled. + + Even when so-called bi-directional level shifters are used, + this technique should be employed when using different bus-widths + on different slots, disabling level shifters to avoid presenting + non-uniform impedance across DATA0-7 & CMD when non-selected + 4-wide slots are left enabled, while accessing 8-wide targets. + + Note that it's not possible to specify multiple regulators + controlled by same GPIO pin, but with different active state. + If one GPIO line is require to switch voltage/routing between + different mmc-slots, specify a vqmmc-supply on one slot, but + not the other. The regulator_disable call on leaving that slot + will implicitly switch the state to support the unmarked slot. + + There's no need to list vqmmc-supply if all the mmc-slots on + a board run at same voltage, and have same width. Examples: mmc_1_4: mmc@1,4 { @@ -40,7 +80,8 @@ Examples: compatible = "mmc-slot"; reg = <0>; vmmc-supply = <&mmc_supply_3v3>; - max-frequency = <42000000>; + vqmmc-supply = <&vqmmc_3v3>; + max-frequency = <52000000>; bus-width = <4>; cap-sd-highspeed; }; @@ -49,7 +90,8 @@ Examples: compatible = "mmc-slot"; reg = <1>; vmmc-supply = <&mmc_supply_3v3>; - max-frequency = <42000000>; + vqmmc-supply = <&vqmmc_1v8>; + max-frequency = <100000000>; bus-width = <8>; cap-mmc-highspeed; non-removable; |