[U-Boot] One u-boot.bin for Raspberry PI 3 and 4 - possible?

[Matthias Brugger]

Hi Geoff,

On 27/09/2019 04:16, Geoff Williams wrote:
> Hi List,
> 
> TLDR: As subject
> 
> I've been following Alexander Graf's uEFI+grub2 presentation on Raspberry PI[1].
> I have it working on PI 3 and 4 and its great but I need to re-compile u-boot
> for each board which means lots of images.
> 
> I would like create a single image to boot grub on PI 3 and 4.
> 
> I did my own investigation but hit a wall. In board/raspberrypi/rpi/rpi.c there
> is a #IFNDEF..#ELSE around the definition of bcm283x_mem_map which selects a
> different memory layout to expose as extern struct mem_map for PI 4 vs anything
> else.
> 
> I did some hacking to expose two mem_map extern structs and pick the right one
> at runtime[2]. Of course this experiment is horrible and breaks all other
> boards:
> 
> board/raspberrypi/rpi/rpi.c
>     static uint32_t rev_type;// = 0x11;
> 
>     struct mm_region *mem_map_b = other_bcm283x_mem_map; /* other PIs */
>     struct mm_region *mem_map_a = bcm2711_bcm283x_mem_map; /* PI 4 */
> 
>     uint32_t get_rpi_hw_ref(void) {
>             /* doesn't work get_board_rev(); */
>              return rev_type;
>     }
> 
> arch/arm/cpu/armv8/cache_v8.c
>     /* before every use of mem_map... */
> 
>       /* nasty hack */
>       struct mm_region *mem_map;
>       if (get_rpi_hw_ref() == 0x11) {
>             mem_map = mem_map_a;
>       } else {
>             mem_map = mem_map_b;
>       }
> 
> rev_type gets set by get_board_rev() but I don't believe this function has been
> called before mem_map is used[3] so my hack always chooses the else branch.
> 
> I'm new to bootloader programming and waiting for a serial cable to arrive so am
> working blind but I suspect I'm up against some kind of chicken and egg problem
> where the memory map needs to be set before the board revision can be extracted
> using the mailbox driver, is anyone able to confirm this or suggest another
> approach?
> 
> My dream is to be able to compile a single u-boot.bin compiled as armv8-a and be
> able to boot any Raspberry PI 3/4 to grub2 from it. Is this realistic?
> 

Yes it is. I was working on this the last weeks and just posted the patches
today. Would be nice if you could test and provide feedback :)

You can find the patch series here:
https://patchwork.ozlabs.org/cover/1168351/

Regards,
Matthias

> Cheers,
> Geoff
> 
> 
> [1] https://www.youtube.com/watch?v=bNL1pd-rwCU
> [2] https://github.com/GeoffWilliams/u-boot/tree/nasty
> [3] If I initialise rev_type as 0x11 then it works on Raspberry PI 4 but if its
>     commented boot fails with rainbow screen which tells me that rev_type wasn't
>     assigned (or didn't contain 0x11...?) before mem_map was used.
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