change the default dtb search path to include default kernel dtbs directory

> Date: Fri, 17 Sep 2021 19:42:29 +0800
> Content-Language: en-US
> 
> On 2021/9/17 19:34, Mark Kettenis wrote:
> >> From: Qu Wenruo <w...@suse.com>
> >> Date: Fri, 17 Sep 2021 19:02:35 +0800
> >>
> >> When booting using U-boot -> systemd-boot (EFI payload) -> kernel on
> >> RK3399, systemd-boot by some bug can't execute its "devicetree" key
> >> correctly to load its proper dtb from files.
> >>
> >> In that case, it will use fallback dtb from U-boot, which can be
> >> out-of-date, and on RK3399, even the latest U-boot contains out-of-date
> >> dtb which can cause problems like invalid opp tables.
> >>
> >> And for systemd-boot, it doesn't provide any board specific dtb, but
> >> completely relies on the EFI environment provided by U-boot, thus if we
> >> can't find a good dtb, the fallback one will be used anyway.
> >>
> >> So this patch will workaround the problem by appending common linux dtbs
> >> directory to the existing "efi_dtb_prefixes" so that for systemd-boot it
> >> can use the existing fdt and boot properly.
> >
> > Why isn't the dtb installed in the standard location?
> 
> Isn't standard location "/dtbs" other than "/dtb"?
> 
> At least kernel puts its dtbs into "/dtbs" by default.

Hmm, well, when I Alexander Graf introduced the code to load an
updated DTB the intention was clearly to load it from the EFI System
Partition (ESP).  I doubt that's where "the kernel" sticks them by
default.  So I suspect the intention is that you copy the DTB to the
/dtb directory on the ESP if needed.  Clearly that isn't what you've
done on your system.

I suspect things have moved on a bit as the discussion in the systemd
thread shows.  One of the new developments is the EFI_DT_FIXUP_PROCOL
feature that is clearly targeted at EFI bootloaders picking and
loading the DT instead of U-Boot.

In this light I would be somewhat reluctant adding more directories to
efi_dtb_prefixes.

> > Slowing the boot process down because distro's can't agree where to
> > put the files is a bit lame...
> 
> Would it be better to make the search path configurable at config time?
> 
> By that each distro should config their dtbs search path, which could
> further optimize the boot sequence by removing all other unnecessary
> prefixes.

Not in my opinion.  I consider it a bad thing if people configure
U-Boot specifically for their distro.  The whole idea of distroboot
and EFI in U-Boot is to be able to boot just any OS with a generic
U-Boot binary.

> Thanks,
> Qu
> 
> >
> >> Signed-off-by: Qu Wenruo <w...@suse.com>
> >> ---
> >>   include/config_distro_bootcmd.h | 2 +-
> >>   1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/include/config_distro_bootcmd.h 
> >> b/include/config_distro_bootcmd.h
> >> index 2627c2a6a541..4ec87483eb65 100644
> >> --- a/include/config_distro_bootcmd.h
> >> +++ b/include/config_distro_bootcmd.h
> >> @@ -151,7 +151,7 @@
> >>            "load ${devtype} ${devnum}:${distro_bootpart} "           
> >>                    "${fdt_addr_r} ${prefix}${efi_fdtfile}"         
> >>    
> >> -  "efi_dtb_prefixes=/ /dtb/ /dtb/current/"                        
> >> +  "efi_dtb_prefixes=/ /dtb/ /dtb/current/ /dtbs/ /dtbs/current/"  
> >>    "scan_dev_for_efi="                                               
> >>            "setenv efi_fdtfile ${fdtfile}; "                         
> >>            BOOTENV_EFI_SET_FDTFILE_FALLBACK                          
> >> --
> >> 2.33.0
> >>
> >>
> 

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