Multi-Soc binary support for i.MX8M Mini/Nano/Plus/? in single boot firmware binary

[Stefano Babic]

Hi Tim,

On 27.05.21 17:41, Tim Harvey wrote:
> Greetings,
> 
> I support various iMX8M PCB's via board/gateworks/venice that are SOM 
> based and we are starting to add SOM's that have different IMX8M variant 
> SoC's on them which for various reasons are not binary compatible. I'm 
> very interested in coming up with a way to make them binary compatible 
> to reduce the number of disk images and boot firmware binaries our users 
> work with (along with the confusion of which one they need to use).

This could be a very nice feature that we had before with i.MX6.

> 
>  From what I see in working thus far with the IMX8M Mini, Nano, and Plus 
> boot firmware differs in the following ways:
> - different primary image offsets
> - different dram config (phy training blob, phy cfg, cfg; which total 
> about 3KiB for each config which varies based on dram type, soc variant, 
> dram topology and bit-mapping)
> - different OCRAM sizes (compat b

Right - we have different DDR firmware, and this should be managed in 
some way.

inary would have to use the minimum
> size ie 256K)

We had this also with i.MX6 - the multibinary approach should work with 
the minimal OCRAM, as it was with MX6(Solo).

> - different ATF binaries
> - different ATF load address
> - different pinmux/padconf/inputsel registers
> - different clk config
> 

Last twos can be solved via detection of CPus and loading different 
setup and/or different DTs.

> The primary image offsets should be able to be dealt with by placing 
> jumps at the various offsets and I believe the rest could be dealt with 
> via runtime code if the SPL could load soc-specific blobs including dram 
> config, ATF, binary firmware blobs from a nice indexed image such as FIT 
> or binman. Currently imx8m SPL's use FIT images that are loaded entirely 
> into OCRAM which becomes an issue when you have enough dram configs that 
> they no longer fit in the OCRAM.

Right - but the trick is to detect the right blob to be loaded. We get 
offset / size in the fitImage for each blob, so we could just load the 
relevant part in OCRAM. But I do not know how this matches with secure 
boot, because HAB should verify the image before loading it.

> 
> Does anyone agree this is doable or is there something they see that 
> would be a show-stopper?

I think it is doable, not easy, and it will be a nice feature, and very 
important for board vendors (as gateworks). I understand that most 
custom projects (products) will chose just one variant, but there also 
cases of real products that was delivered as "lite" and "pro", with 
different SOCs.

> 
> I'm not all that familiar with the merits of binman fs FIT images... I 
> think they were developed for different things.

I think so - I will tend to work with fitImage, and I think it suits for 
these needs if the issues with the size of OCRAM are solved (like a 
partial or selective load).

> I'm not sure if 
> either/both are suited for what I'm talking about regarding having the 
> SPL raw load binary blobs vs having them tacked onto a FIT image.
> 
> I'm not sure if the imx8mq has enough in common to be able to do this 
> with either, in fact I'm not even clear with SoC that is (is it what NXP 
> calls i.MX 8M?)

Someone from NXP should better explain this ;-)

Best regards,
Stefano

> 
> Best regards,
> 
> Tim


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