[U-Boot] Using sspi for hardware detection?

[Simon Goldschmidt]

On Wed, Nov 27, 2019 at 1:58 PM Romain Naour <romain.naour at smile.fr> wrote:
>
> Hello,
>
> I'm working on a modular socfpga based system with several optional boards.
> Each optional board contain a board ID that can be read through a SPI bus.
>
> Since we want just read the board ID, we used manually the sspi command,
> something like:
>
> => sspi 1:1.0 8 0
> 42
>
> But it seems that the sspi command can't be used in a uboot script. sspi seems
> only used to manually test spi drivers.
>
>
> If we compare with i2c command, we have a i2c read to memory:
>
> i2c read chip address[.0, .1, .2] length memaddress - read to memory
>
> Why there is no such feature for spi ?

Probably because noone has needed it so far.

> Is there an interest to evolve the sspi command to add a read to memory?
>
> sspi <bus id>: <chip select>.<mode> <bit length> <data> <memaddress>

If you need it and provide a decent patch, I could probable get accepted...

>
> By looking at existing code, it seems that hardware detection in uboot is
> handled by architecture/board specific code to set custom environment variable
> like "fpgatype" [1] or "unit_ident" "unit_serial" [2] (misc_init_r).
>
> What do you recommend?
> Implement a custom misc_init_r() for hardware detection?

How is that related? How does reading to memory help you with knowing the hw
type in scripts?

Anyway, I think board_late_init is a better fit than misc_init_r,
which is rather
meant to be a platform thing and vining can only use it because socfpga
doesn't need it otherwise.

Regards,
Simon

>
> [1]
> https://gitlab.denx.de/u-boot/u-boot/blob/master/arch/arm/mach-socfpga/misc_gen5.c#L139
> [2]
> https://gitlab.denx.de/u-boot/u-boot/blob/master/board/softing/vining_fpga/socfpga.c#L48
>
> Best regards,
> Romain
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