[LEDE-DEV] MT7688 SPI confusion

[Daniel Golle]

Hi!

I'm currently trying to get SPI with two devices connected to work on
MT7688 and noticed that the spi-mt7621 driver got a pretty weird
work-around going on: if CS# is set it does only half-duplex transfers
which if CS# is not set it does full-duplex. John has then disabled
full-duplex alltogether on the Chaos Calmer branch [1].
What I'm trying to achieve is to use WrtNode2R's spi-bridge [2] to
communicate with the STM32 MCU running RT-Thread. This somehow works
in Chaos Calmer when using WrtNode modified tree [3] but doesn't
work well on LEDE git HEAD... Any ideas?

Apart from the spi-based rpc/console the Wrtnode2R comes with a flash
tool for the STM32 [4] -- it would of course be much nicer to have a
SPI backend for stm32flash to achieve the same thing. To be able to
implement that I'd like to first understand what is needed to get SPI
fixed so that the not-very-beautiful existing tooling can be replaced.

Any experience with more than one SPI slave connected to MT76xx SoCs,
stm32flash via SPI and general ideas/inspiration on bridging with RTOS
running on MCUs next to an embedded Linux SoC is more than welcome :)


Cheers


Daniel



[1]:
commit 877ee7d7f54847b4e95c1feb6de0f5413e2fe7a1
Author: John Crispin <blogic at openwrt.org>
Date:   Tue Apr 19 21:01:34 2016 +0000

    ralink: add spi fix
    
    the fullduplex on CS1 is broken. remove the fullduplex support and run on
    plain half duplex on both CS lines.
    
    Signed-off-by: John Crispin <blogic at openwrt.org>
    
    git-svn-id: svn://svn.openwrt.org/openwrt/branches/chaos_calmer@49201 3c298f89-4303-0410-b956-a3cf2f4a3e73

[2]: https://github.com/WRTnode/openwrt-packages/blob/master/wrtnode/spi-bridge/src/main.c

[3]: https://github.com/WRTnode/openwrt

[4]: https://github.com/WRTnode/openwrt-packages/blob/master/wrtnode/WRTnode2r-stm32/src/main.c#L57