diff options
Diffstat (limited to 'Documentation/devicetree/bindings/spi/spi-controller.yaml')
| -rw-r--r-- | Documentation/devicetree/bindings/spi/spi-controller.yaml | 33 |
1 files changed, 31 insertions, 2 deletions
diff --git a/Documentation/devicetree/bindings/spi/spi-controller.yaml b/Documentation/devicetree/bindings/spi/spi-controller.yaml index 1b56d5e40f1f..06786f1b43d2 100644 --- a/Documentation/devicetree/bindings/spi/spi-controller.yaml +++ b/Documentation/devicetree/bindings/spi/spi-controller.yaml @@ -42,6 +42,33 @@ properties: cs2 : &gpio1 1 0 cs3 : &gpio1 2 0 + The second flag of a gpio descriptor can be GPIO_ACTIVE_HIGH (0) + or GPIO_ACTIVE_LOW(1). Legacy device trees often use 0. + + There is a special rule set for combining the second flag of an + cs-gpio with the optional spi-cs-high flag for SPI slaves. + + Each table entry defines how the CS pin is to be physically + driven (not considering potential gpio inversions by pinmux): + + device node | cs-gpio | CS pin state active | Note + ================+===============+=====================+===== + spi-cs-high | - | H | + - | - | L | + spi-cs-high | ACTIVE_HIGH | H | + - | ACTIVE_HIGH | L | 1 + spi-cs-high | ACTIVE_LOW | H | 2 + - | ACTIVE_LOW | L | + + Notes: + 1) Should print a warning about polarity inversion. + Here it would be wise to avoid and define the gpio as + ACTIVE_LOW. + 2) Should print a warning about polarity inversion + because ACTIVE_LOW is overridden by spi-cs-high. + Should be generally avoided and be replaced by + spi-cs-high + ACTIVE_HIGH. + num-cs: $ref: /schemas/types.yaml#/definitions/uint32 description: @@ -125,8 +152,9 @@ patternProperties: spi-rx-bus-width: description: Bus width to the SPI bus used for read transfers. + If 0 is provided, then no RX will be possible on this device. $ref: /schemas/types.yaml#/definitions/uint32 - enum: [1, 2, 4, 8] + enum: [0, 1, 2, 4, 8] default: 1 spi-rx-delay-us: @@ -136,8 +164,9 @@ patternProperties: spi-tx-bus-width: description: Bus width to the SPI bus used for write transfers. + If 0 is provided, then no TX will be possible on this device. $ref: /schemas/types.yaml#/definitions/uint32 - enum: [1, 2, 4, 8] + enum: [0, 1, 2, 4, 8] default: 1 spi-tx-delay-us: |