[U-Boot] [PATCH] fdt: Add warning about CONFIG_OF_EMBED

[Lukasz Majewski <lukma@denx.de>]

Hi Simon,

> Hi Lukasz,
> 
> On Wed, 19 Dec 2018 at 03:11, Lukasz Majewski <lukma@denx.de> wrote:
> >
> > Dear Simon and Simon,
> >  
> > > Am 05.12.2018 um 14:57 schrieb Simon Glass:  
> > > > This option has crept into use with some boards. Add a warning
> > > > to try to prevent this.
> > > >
> > > > As an example:
> > > >     https://lists.denx.de/pipermail/u-boot/2017-September/304966.html  
> > >
> > > We have just discussed this in another thread. There seem to be
> > > ~109 defconfigs in the tree that enable OF_EMBED.
> > >
> > > I doubt all of them do this for fun, so we might want to collect
> > > the reasons they do so. I do know two:
> > >
> > > - socfpga_stratix10_defconfig needs this to get a correct
> > > u-boot-spl.hex
> > > - I would need it to ensure in SPL, the DTB is in one block with
> > > the other readonly parts. Without OF_EMBED, we have '.text',
> > > '.bss', DT.  
> >
> > Another use case is imx6:
> >
> > When I want to use SPL's embedded DTB for early init, with
> > OF_SEPARATE I get fdt_blob = (ulong *)&__bss_end; ,which points me
> > to 0x18200060, which is in DDR (and there is either garbage nor DDR
> > is not initialized at all).
> >
> > The above looks like the __bss_end is for u-boot proper.
> >
> > The workaround (for now) is to have OF_EMBED, which assigns
> > gd->fdt_blob = __dtb_dt_spl_begin [1], and this is a correct
> > address.
> >
> > Hence, I'm wondering if shall I assign:
> > gd->fdt_blob = __dtb_dt_spl_begin;
> >
> > in my early SPL code (and do not use fdt_setup() function at all in
> > SPL) ?  
> 
> Or you could update fdt_setup() to do what you want (perhaps with a
> new CONFIG?).

I've found the root cause of this problem....

For the board I had not defined CONFIG_SPL_SEPARATE_BSS. After
providing it the OF_SEPARATE can be used (and dtb is appended between
SPL binary and bss (in SDRAM) region.

> 
> >
> > Moreover, defining board_fdt_blob_setup() for _each_ IMX6 board
> > which would switch to DM_MMC in SPL seems like an no acceptable
> > solution.
> >
> >
> > [1] - ./spl/dts/dt-spl.dtb.S:3:.global __dtb_dt_spl_begin  --> Looks
> > like __dtb_dt_spl_begin is exactly for this purpose.  
> 
> Regards,
> Simon




Best regards,

Lukasz Majewski

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