Re: barebox PBL question

[Sascha Hauer <s.hauer@pengutronix.de>]

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/zbarebox.map --gc-sections -static -o
> >> arch/arm/pbl/zbarebox -e pbl_start -T arch/arm/pbl/zbarebox.lds
> >> --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 ;)

Sascha

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