Aspeed SPI driver upstreaming

[Patrick Williams]

Cedric, Joel,

There is currently the aspeed-smc driver[1], which is upstreamed, but only
supports spi-nor devices.  There also a more generic spi-aspeed
driver[2], which might only exist in Facebook kernel trees, that
supports all spi devices but it doesn't do the calibration work.

I made some changes to the spi-aspeed driver recently in order to get it
to somewhat support TPM 2.0 devices (*).  The spi-aspeed driver also
already supported generic spi-nor MTD devices, but just at a slower
speed than aspeed-smc due to missing the calibration routines.

Tao mentioned to me that there was a discussion at one of the F2F events
in 2019 about combining those two drivers and getting them upstreamed,
but that the hang-up was getting upstream mtd and spi subsystems to
agree on how to handle calibration routines in the spi subsystem?  I
can't seem to find anything about this on the LKML.  Do either of you
know where that discussion went and what the current state / plans of
upstreamming a generic Aspeed SPI driver are?

[1] https://github.com/openbmc/linux/blob/dev-5.3/drivers/mtd/spi-nor/aspeed-smc.c
[2] https://github.com/facebook/openbmc-linux/blob/dev-5.0/drivers/spi/spi-aspeed.c

(*) The Aspeed SPI master is half-duplex and the TPM SPI spec effectively
    requires full duplex hardware.  I did some workarounds to get it to work
    with one particular part and need to work with the vendor and upstream
    to figure out the best way to reliably handle half-duplex SPI masters.
-- 
Patrick Williams
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