[U-Boot] Using sspi for hardware detection?

[Romain Naour]

Hi,

Le 27/11/2019 à 21:13, Simon Goldschmidt a écrit :
> 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...

Ok I'll take a look how to implement this.

> 
>>
>> 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?

Sorry, actually this is another possibility.

The first possibility is evolve the sspi command to add <memaddress>. This allow
to use a script working on memory containing the data received from the spi bus.
For my use case, it would allow to get the board ID in memory and use an uboot
script analyze which board ID has been read.

The second possibility is to use misc_init_r (or as you suggest board_late_init)
in a board specific code (board/<customer>/<board_name>/socfpga.c) to access the
spi bus and set custom environment variable. These environment variable are
later used by uboot script.

I would like an advice on the best implementation.
I believe modifying sspi command can be the way to go since it can be used for
other use case.

> 
> 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.

Thanks for your feed back!

Best regards,
Romain


> 
> 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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