[PATCH v4 0/4] spi: amlogic: meson-spicc: Use pinctrl to drive CLK line when idle

[Amjad Ouled-Ameur]

Between SPI transactions, all SPI pins are in HiZ state. When using the SS
signal from the SPICC controller it's not an issue because when the
transaction resumes all pins come back to the right state at the same time
as SS.

The problem is when we use CS as a GPIO. In fact, between the GPIO CS
state change and SPI pins state change from idle, you can have a missing or
spurious clock transition.

Set a bias on the clock depending on the clock polarity requested before CS
goes active, by passing a special "idle-low" and "idle-high" pinctrl state
and setting the right state at a start of a message.

Signed-off-by: Amjad Ouled-Ameur <aouledameur at baylibre.com>
---
Changes in v4:
- Fixed documentation by defining pinctrl-x.
- Link to v3: https://lore.kernel.org/r/20221004-up-aml-fix-spi-v3-0-89de126fd163@baylibre.com

Changes in v3:
- Fixed documentation by removing pinctrl states as they are not mandatory.
- Link to v2: https://lore.kernel.org/r/20221004-up-aml-fix-spi-v2-0-3e8ae91a1925@baylibre.com

---
Amjad Ouled-Ameur (4):
      spi: dt-bindings: amlogic, meson-gx-spicc: Add pinctrl names for SPI signal states
      spi: meson-spicc: Use pinctrl to drive CLK line when idle
      arm64: dts: meson-gxl: add SPI pinctrl nodes for CLK
      arm64: dts: meson-gxbb: add SPI pinctrl nodes for CLK

 .../bindings/spi/amlogic,meson-gx-spicc.yaml       | 75 ++++++++++++++--------
 arch/arm64/boot/dts/amlogic/meson-gxbb.dtsi        | 14 ++++
 arch/arm64/boot/dts/amlogic/meson-gxl.dtsi         | 14 ++++
 drivers/spi/spi-meson-spicc.c                      | 39 ++++++++++-
 4 files changed, 113 insertions(+), 29 deletions(-)
---
base-commit: e35184f321518acadb681928a016da21a9a20c13
change-id: 20221004-up-aml-fix-spi-c2bb7e78e603

Best regards,
-- 
Amjad Ouled-Ameur <aouledameur at baylibre.com>