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Diffstat (limited to 'dts/Bindings/spi/spi-controller.yaml')
| -rw-r--r-- | dts/Bindings/spi/spi-controller.yaml | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/dts/Bindings/spi/spi-controller.yaml b/dts/Bindings/spi/spi-controller.yaml index 1b56d5e40f..5f50581010 100644 --- a/dts/Bindings/spi/spi-controller.yaml +++ b/dts/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: |