+Tom, Wolfgang, Masahiro

Hi Kever,

On 12 December 2017 at 21:35, Kever Yang kever.yang@rock-chips.com wrote:

Hi Simon,

This is not the topic about disable the relocate feature in U-Boot

proper.

My target is re-use kernel dtb in U-Boot and U-Boot can work properly even if some of dts node in kernel is broken.

• U-Boot mark a set of driver as u-boot,dm-pre-reloc, suppose to able to get into U-Boot shell with them. dram, syscon, serial, clock, pinctrl, emmc,

and etc. In this case we can always make U-Boot works and get into shell.

• When relocate, I would like to read dtb from kernel and use it for U-Boot

driver. In this case, we can get periph driver setting for different board from kernel dtb, what we need most are: power/pmic, display, charger, input key and etc.

The problem is, the dm architecture now always init all the driver from dtb after relocate, If anything missin in kernel dtb, the U-Boot hang there. What I met now in rockchip kernel(same in different SoCs) is:

• no stdout in chosen, we use cmdline instead;
• debug uart node not enabled; we may use ttyFIQ driver instead of uart

driver for it.

• no alias for emmc/sd, which is much in U-Boot;
• compaptible for syscon may different, kernel may use "syscon",

"simple-mfd" only, but U-Boot need "rockchip,rk3228-grf" for GRF and "rockchip,rk3228-PMU" for PMU and etc. Of cause I can update kernel source, but as you can see we are not able to cover all the case because kernel may have different use with U-Boot.

One option is to fix up the kernel DT using code, e.g. in the fix_fdt() function.

Another is to fix the Linux DT. I think the above could all be fixed without complaints from Linux. Could you try that? We should use exactly the same DT for Linux and U-Boot. Even the u-boot,dm-* should be able to be sent upstream, based on my understanding of a discussion at ELCE.

If we do not need to re-init all the driver after relocate, or re-use the driver data, then we can have a robust U-Boot only depends on U-Boot dtb with dm-pre-reloc, and we can have a good compatibility U-Boot with kernel dtb support for different board/periph. Then U-Boot focus on SoC support, kernel focus on all kinds of board/periph support, U-Boot need to sync periph driver from kernel, so that if kernel works then U-Boot also works, developers do not need to develop one for kernel and one for U-Boot.

Could you help to make a demo patch about how to re-use the driver-data of pre-reloc to post-reloc?

I don't think this is a good way to solve the problem. Masahiro has suggested that we eliminate pre-relocatiom U-Boot when using SPL, so in this case we would not have the ability to use a separate DT for pre-relocation and post-relocation U-Boot.

As to your goal of avoiding device re-init, Masahiro's idea (if implemented) would avoid the need to re-init (SPL would still do it but that is a separate program).

That said, I will see if I can come up with a patch to allow access to driver data from a previous driver-model data structure. I worry that it would be a bit fiddly though.

Regards, Simon