barebox PBL question

Wadim Egorov w.egorov at
Tue Feb 14 01:54:49 PST 2017

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.


> What you'll need additionally is a tool which encapsulates the image into
> a SoC specific container suitable for the ROM.
> Sascha

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