[edk2-devel] How /sys/firmware/fdt getting created

[Laszlo Ersek]

+Leif, comment at bottom

On 10/30/19 09:16, Prabhakar Kushwaha wrote:
> On Wed, Oct 30, 2019 at 1:14 PM Ard Biesheuvel
> <ard.biesheuvel at linaro.org> wrote:
>>
>> On Wed, 30 Oct 2019 at 08:36, Prabhakar Kushwaha
>> <prabhakar.pkin at gmail.com> wrote:
>>>
>>> On Wed, Oct 30, 2019 at 12:43 PM Ard Biesheuvel
>>> <ard.biesheuvel at linaro.org> wrote:
>>>>
>>>> On Tue, 29 Oct 2019 at 18:17, Prabhakar Kushwaha
>>>> <prabhakar.pkin at gmail.com> wrote:
>>>>>
>>>>> Hi All,
>>>>>
>>>>> I am working on Ubuntu-18.04 with UEFI on ARM64(64 bit) platform. The
>>>>> UEFI used is having ACPI tables.
>>>>>
>>>>> I am trying to understand where and how /sys/firmware/fdt is getting
>>>>> created. is it created by UEFI or grub and passed to Linux?
>>>>>
>>>>
>>>> Neither. It is created by Linux itself.
>>>>
>>>>
>>>>
>>>
>>> Thanks Ard,
>>>
>>> Can you please point me the code where it is getting created.
>>> I want to add below in /sys/firmware/fdt.
>>>
>>> #size-cells = <0x02>;
>>> #address-cells = <0x02>;
>>>
>>
>> Actually, in your case it is GRUB not the kernel that creates the FDT.
>> It does this to pass the initrd information.
>>
>> So if you want to add these properties, you should add them there.
>>
>> Can you explain why doing this is necessary?
> 
> I am trying to test kexec -p (kdump feature) on CentOS-release
> 7.7.1908 and Ubuntu-18.04 distributions.
> 
>  "kexec -p" command show error on Ubuntu. While no error on CentOS
> 
> CentOS:
> $ kexec -p /boot/vmlinuz-`uname -r` --initrd=/boot/initramfs-`uname
> -r`.img --reuse-cmdline
> $    ==> No error
> 
> Ubuntu
> $ kexec -p /boot/vmlinuz-`uname -r` --initrd=/boot/initrd.img-`uname
> -r` --reuse-cmdline
> $ kexec: elfcorehdr doesn't fit cells-size.
> $ kexec: setup_2nd_dtb failed.
> $ kexec: load failed.
> $ Cannot load /boot/vmlinuz-5.4.0-rc4+
> 
> Note: Both CentOS and Ubuntu has Linux-5.4-rc4 tag.
> 
> When i debugged further reason for Ubuntu error is due to
> address-cells and size-cells as "1"
> log from kexec tool :-
> load_crashdump_segments: elfcorehdr 0x7f7cbfc000-0x7f7cbff7ff
> read_1st_dtb: found name =dtb_sys  /sys/firmware/fdt
> get_cells_size: #address-cells:1 #size-cells:1
> 
> On CentOS both values are "2".
> log from kexec tool :-
> load_crashdump_segments: elfcorehdr 0xbf98bf0000-0xbf98bf33ff
> read_1st_dtb: found nmae=dtb_sys /sys/firmware/fdt
> get_cells_size: #address-cells:2 #size-cells:2
> 
> Note: Kexec tool read values from /sys/firmware/fdt.
> 
> I am trying to figure out why 2 distributions showing different values.

http://git.savannah.gnu.org/cgit/grub.git/commit/?id=347210a5d5ce655b95315f320faa515afb723c11

Ubuntu probably ships a grub version that lacks this commit.

(The commit was first released as part of upstream grub-2.04. I have no
idea what version of grub is shipped in the CentOS distro you mention
above -- it could be based upon upstream 2.04, or the upstream patch may
have been backported to CentOS.)

Thanks
Laszlo


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