[Pkg-raspi-maintainers] raspi3-firmware: container awareness and device tree handling

[Matthias Luescher]

Hi Michael


> Thanks for the patches. The modification to debian/kernel/postinst.d/raspi3-firmware
> could be simplified, I think. Why not just:
>
> [ -e "${dtb_path}/bcm2836-rpi-2-b.dtb"] && cp ${dtb_path}/bcm2836-rpi-2-b.dtb
> /boot/firmware/bcm2709-rpi-2-b.dtb
> [ -e "${dtb_path}/bcm2837-rpi-3-b.dtb"] && cp ${dtb_path}/bcm2837-rpi-3-b.dtb
> /boot/firmware/bcm2710-rpi-3-b.dtb
>

This would indeed simplify the script. However, with my modification I
tried to keep the same logic as before:

   1. First we check that all required pieces are in place (kernel, initial
   ramdisk, device tree binary or binaries).
   2. Only copy the required pieces to /boot/firmware if everything is
   available, otherwise print a message and do a exit 0.

Your proposed modification would silently ignore if the device tree
binaries could not be retrieved (e.g. because they are missing, were
renamed or moved to another location).

We could then even end up with an inconsistent system (new kernel, device
tree binaries from a previous kernel installation).

I even though about doing an exit 1 instead of an exit 0 but I think the
exit 0 is supposed to cover the case if the raspi3-firmware package gets
installed prior to the kernel package.


> Also, can you explain the following syntax?
>
> : chroot detected - skip mount point check
>

The ":" is a "no operation". The stuff behind it is just comment. A
logically equivalent statement would be:
true # chroot detected - skip mount point check


Can you outline whether there’s a downside to setting cma=64M?
>

On arm64 this has no impact at all since CONFIG_CMA_SIZE_MBYTES is anyway
set to 64. On armmp-lpae CONFIG_CMA_SIZE_MBYTES is set to 16. So this will
reduce the generally available RAM a bit but it allows the vc4 driver to
initialize the GPU.


> Are the 64M then reserved for graphics, and can no longer be used as
> general purpose memory?
>

Unfortunately I am not familiar with the details. The kernel documentation
looks like this:

CONFIG_CMA:

This enables the Contiguous Memory Allocator which allows other
subsystems to allocate big physically-contiguous blocks of memory.
CMA reserves a region of memory and allows only movable pages to
be allocated from it. This way, the kernel can use the memory for
pagecache and when a subsystem requests for contiguous area, the
allocated pages are migrated away to serve the contiguous request.


Therefore I guess that the access to the reserved area is restricted and
can not be fully used for general purpose stuff.


> What’s the dosfstools dependency required for?
>

dosfstools contains fsck.vfat. If this binary is missing, the
script debian/initramfs-tools/hooks/raspi3-firmware-fsck will fail.

Please let me know if I should do changes to my patches. I can then re-test
the stuff.

Best regards
Matthias
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