[0/4] SPI 3WIRE fixes and highz turnaround

Message

Linus Walleij Sept. 3, 2018, 9:50 p.m. UTC

During review of the TPO TPG110 driver[1] it was noted that the
protocol used is a variant of SPI 3WIRE[2] and the panel should
be a SPI child device.[3]

While trying to repurpose the driver to use the brand new
3WIRE support in SPI, I ran into a few rough edges (patches
1 & 2). If these are OK with Lorenzo they can probably be
applied as-is.

Then I had to add support for the special "high impedance
turn-around cycle" to the SPI core and the GPIO bit-banging
driver to be able to support the panel.

It is now working fine and I have patches to use the panel
as an SPI child device, but these patches are needed to
get it going.

References:
[1]:
https://lists.freedesktop.org/archives/dri-devel/2018-July/181848.html
[2]:
http://aitendo3.sakura.ne.jp/aitendo_data/product_img/lcd/tft/T43P00/TPG110%20Customer%20Spec_0.6.pdf
[3]:
https://lists.freedesktop.org/archives/dri-devel/2018-July/181993.html

Linus Walleij (4):
  spi: core: Allow both TX and RX transfers in 3WIRE
  spi: gpio: Fix reading for 3WIRE
  spi: Add a DT binding for high impedance turnaround
  spi: gpio: Support 3WIRE high impedance turn-around

 .../devicetree/bindings/spi/spi-bus.txt       |  4 ++
 drivers/spi/spi-gpio.c                        | 41 +++++++++++++++----
 drivers/spi/spi.c                             | 17 ++++++--
 include/linux/spi/spi.h                       |  1 +
 4 files changed, 52 insertions(+), 11 deletions(-)