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[v2,0/2] Add support for components requiring trailing clock after transfer

Message ID cover.1646060734.git.christophe.leroy@csgroup.eu (mailing list archive)
Headers show
Series Add support for components requiring trailing clock after transfer | expand

Message

Christophe Leroy Feb. 28, 2022, 3:15 p.m. UTC 
Some components require a few clock cycles with chipselect off before
or/and after the data transfer done with CS on.

Typically IDT 801034 QUAD PCM CODEC datasheet states "Note *: CCLK
should have one cycle before CS goes low, and two cycles after
CS goes high".

The cycles "before" are implicitely provided by all previous activity
on the SPI bus. But the cycles "after" must be provided in order to
achieve the SPI transfer.

In order to use that kind of component, implement a new option for
SPI slaves in order to implement trailing clock of a given number of
bits with ChipSelect off at the end of the transfer.

This is based on a discussion we had a few years ago, see
https://lore.kernel.org/linux-spi/20160824112701.GE22076@sirena.org.uk/

IDT 801034 QUAD PCM CODEC datasheet can be found at
https://www.renesas.com/eu/en/document/dst/821034-data-sheet?language=en&r=24763

Changes in v2:
- Provide the number of wanted clock cycles instead of just a bool. 

Christophe Leroy (2):
  spi: Add optional number of additional clock cycles to be generated
  spi: fsl-spi: Implement trailing bits

 .../bindings/spi/spi-peripheral-props.yaml    |  5 +++++
 drivers/spi/spi-fsl-spi.c                     | 21 +++++++++++++++++--
 drivers/spi/spi.c                             |  7 +++++--
 include/linux/spi/spi.h                       |  1 +
 4 files changed, 30 insertions(+), 4 deletions(-)