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

[Prabhakar Kushwaha]

Hi Bhupesh,

On Fri, Nov 1, 2019 at 1:59 AM Bhupesh Sharma <bhsharma at redhat.com> wrote:
>
> Hi Prabhakar,
>
> On Wed, Oct 30, 2019 at 1:47 PM Prabhakar Kushwaha
> <prabhakar.pkin at gmail.com> 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.
>
> There are a couple of things I can suggest:
>
> 1. Try to see if it is a kexec-tools specific issue or is the kernel
> itself passed an incorrectly fixed DTB (by grub?) with incorrect
> #address-cells and #size-cells values (in the past I have seen
> kexec-tools sometimes reports incorrect #address-cells and #size-cells
> values, but they should be fixed in the newer kexec-tools versions):
>
> a). Can you check the kexec-tools version and share the same:
> $ kexec -v
>
> b). Using 'dtc' tool, you can confirm if it reports a correct
> #address-cells and #size-cells values:
> # dtc -I dtb -O dts /sys/firmware/fdt | grep cells | less
>
> For e.g on my fedora arm64 system, it reports:
>     #address-cells = <0x2>;
>     #size-cells = <0x2>;
>
> 2a). If its not a kexec-tools specific issue, it is most probably a
> bootloader (grub?) issue in your case:
>
> For e.g. I use the following grub2 on my Fedora arm64 board:
> <https://github.com/rhboot/grub2>
> and <https://github.com/rhboot/grub2/blob/master/grub-core/loader/efi/fdt.c#L34>
> contains the changes to send the correct #address-cells and
> #size-cells values to Linux (and hence user-space tools like
> kexec-tools later).
>
> I believe the same grub2 is used (backported) for CentOS, so things
> should be fine there.
>
> 2b). I see that the latest devel branch of ubuntu grub2
> (<https://code.launchpad.net/ubuntu/+source/grub2>) also contains this
> fix, but I am not sure which grub2 version you have on your ubuntu
> machine.
>

Ubuntu 18.04 has grub 2.02. When i migrated to grub 2.05, this issue
is not there.
Most probably the patch which is mentioned by Laszlo done the fix.

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

Thanks
--pk

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