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| author |  H. Nikolaus Schaller <hns@goldelico.com>
| 2020-12-09 10:57:44 +0100 |
|---|---|---|
| committer |  Mark Brown <broonie@kernel.org>
| 2020-12-11 13:23:09 +0000 |
| commit | 2fee9583198eb97b5351feda7bd825e0f778385c (patch) | |
| tree | 9ec7014d0d4949e9d6b94259fbf769a64b4d2a60 /Documentation/devicetree | |
| parent | Merge series "spi: spi-geni-qcom: Use gpio descriptors for CS" from Stephen B... (diff) | |
| download | linux-2fee9583198eb97b5351feda7bd825e0f778385c.tar.gz linux-2fee9583198eb97b5351feda7bd825e0f778385c.tar.bz2 linux-2fee9583198eb97b5351feda7bd825e0f778385c.zip | |
spi: dt-bindings: clarify CS behavior for spi-cs-high and gpio descriptors
Behavior of CS signal in combination of spi-cs-high and gpio descriptors
is not clearly defined and documented. So clarify the documentation
Cc: linus.walleij@linaro.org
Cc: linux-gpio@vger.kernel.org
Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/3bed61807fff6268789e7d411412fbc5cd6ffe2a.1607507863.git.hns@goldelico.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Diffstat (limited to 'Documentation/devicetree')
| -rw-r--r-- | Documentation/devicetree/bindings/spi/spi-controller.yaml | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/Documentation/devicetree/bindings/spi/spi-controller.yaml b/Documentation/devicetree/bindings/spi/spi-controller.yaml index 1b56d5e40f1f..5f505810104d 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: |