[PATCH v2 0/2] spi: support devices with no wire in one direction

[Cole Munz <Munzzyy1@proton.me>]

The Flipper One display bus has no MISO wire. That pin is the
end-of-frame GPIO. The device tree says so with spi-rx-bus-width = <0>,
but the uclass dropped the value and the Rockchip driver clocked the
receive FIFO anyway, discarding every byte. Reported at
https://github.com/flipperdevices/u-boot/issues/33 from the boot log
there; Alexey has since confirmed the fix on the hardware.

Patch 1 maps bus width 0 to SPI_NO_TX/SPI_NO_RX, validates transfers
against the bits in dm_spi_xfer() and adds a sandbox test. Patch 2 has
the Rockchip driver pick its transfer mode from those bits, so the
unused FIFO stays out of the transfer.

Both went out on their own before:

https://lore.kernel.org/all/10e92a74c8a22cc2cd54f5dcccc31594016d4263.1787015208.git.Munzzyy1@proton.me/
https://lore.kernel.org/all/69c35eba7ee1a353107459b8f8032e92506a3fb1.1787045568.git.Munzzyy1@proton.me/

Rolled into one series now, since patch 1 has no user by itself. The
rk_spi mail had also gone out as a reply into the uclass thread, which
is what made b4 read it as a v2 of the prerequisite. Clean thread this
time. Sorry for the noise.

Changes in v2:
- validate NO_RX/NO_TX centrally in dm_spi_xfer() and return -EINVAL,
  matching Linux __spi_validate(), with a sandbox test for both
  rejections (suggested by Quentin)
- reworded the transfer mode comment in rk_spi.c claim_bus (Quentin)
- collected Alexey's Tested-by on patch 2 (Flipper One, warning gone,
  transmit-only display still works)
- added the maintainers get_maintainer.pl lists for the touched files
- one series with a cover letter instead of two stray patches

Cole Munz (2):
  spi: Handle spi-{tx,rx}-bus-width 0 as SPI_NO_TX/SPI_NO_RX
  spi: rockchip: skip the unused FIFO direction on a one-wire device

 drivers/spi/rk_spi.c     | 27 ++++++++++++++++++++++----
 drivers/spi/spi-uclass.c | 16 ++++++++++++++++
 include/spi.h            |  2 ++
 test/dm/spi.c            | 41 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 82 insertions(+), 4 deletions(-)


base-commit: 527115ef6783cec49e5610c523c124b399011361
-- 
2.55.0