barebox PBL question

Wadim Egorov w.egorov at
Tue Feb 14 03:34:37 PST 2017

On 14.02.2017 11:48, Sascha Hauer wrote:
> On Tue, Feb 14, 2017 at 10:54:49AM +0100, Wadim Egorov wrote:
>> On 13.02.2017 20:22, Sascha Hauer wrote:
>>> On Mon, Feb 13, 2017 at 04:13:48PM +0100, Wadim Egorov wrote:
>>>> Hi,
>>>> I would like to add SPL support for the RK3288 SoC to barebox. But I am
>>>> facing
>>>> a few problems.
>>>> The maximum size of the SPL image which the ROM code will read is 32KB.
>>>> I was thinking to use the PBL feature for the SPL part. But using the
>>>> the pbl code (with decompression) seems to be not a good idea, because
>>>> it's size
>>>> is already about 30K. I think this is an overhead.
>>> In a test build here the pbl code is 6KiB. The rest is the devicetree
>>> included in the binary (which I disabled in the test build). The dtb can
>>> be compressed which should give you enough space even in 32KiB.
>> OK, I think I checked the wrong file size. pblb is the bare binary file
>>>> But now I wonder how to generate two different images with a single build.
>>>> A SPL image, which should not exceed 32K and a barebox.
>>>> I have problems to fully understand the PBL mechanism.
>>>> Why are the builds always adding the barebox.bin images to the PBL part?
>>> The idea is to create an image that contains the PBL and attached to it
>>> the compressed barebox image. If your ROM only allows a certain image
>>> size then make sure the PBL is small enough and tell the ROM to only
>>> load the PBL part of the image. Ideally the PBL then detects from where
>>> the PBL is loaded (by reading back the bootsource the SoC provides) and
>>> reads the rest of the image into SDRAM (or, for sake of simplicity, the
>>> whole image inculding PBL again)
>> ty for clarification
>>>> Here is an example, cat .zbarebox.cmd
>>>> ld -EL  -Map arch/arm/pbl/ --gc-sections -static -o
>>>> arch/arm/pbl/zbarebox -e pbl_start -T arch/arm/pbl/
>>>> --start-group  common/built-in-pbl.o [...]  arch/arm/pbl/piggy.shipped.o
>>>> --end-group
>>>> piggy.shipped.o is barebox.bin, which is added in piggy.shipped.S:
>>>> .incbin "arch/arm/pbl/piggy.shipped"
>>> You should use PBL_MULTI_IMAGES instead. In fact, the existing Rockchip
>>> port already does this.
>>> I think your entry function should look something like:
>>> ENTRY_FUNCTION(start_rk3288_phycore_som, r0, r1, r2)
>>> {
>>> 	arm_cpu_lowlevel_init();
>>> 	if (inside_sdram(get_pc()))
>>> 		barebox_arm_entry(0x0, SZ_1G, fdt);
>>> 	rk3288_phycore_setup_sdram();
>>> 	jump_back_to_rom();
>>> }
>>> I don't know how jump_back_to_rom() should be implemented. Do you have
>>> to return from the entry function to the ROM or does the ROM provide some API
>>> which can be used to chainload the rest of the image?
>> No, there is no API in the ROM.
>> In u-boot the spl will return to bootrom in board_init_f(), then bootrom
>> loads u-boot binary.
> The ENTRY_FUNCTION macro is not prepared for returning to the caller.
> You'll have to replace it with something like:
> void __section(.text_head_entry_start_rk3288_phycore_som)
> start_start_imx6q_sabrelite(uint32_t r0, uint32_t r1, uint32_t r2)
> This makes sure the link register is preserved and is jumped to at the
> end of the function.
> You could also send me some hardware, I could provide some better help
> then. I know this early bringup can be tricky ;)

I will send you our hardware. After the redesign :)

> Sascha

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