Re: The state of Arm64 on Raspberry Pi (and its Documentation
Hi Arnd,
On 2020.03.31 19:33, Arnd Bergmann wrote:
There is no need to use ACPI when using the UEFI boot path, that can
just as well work with a normal DT.
But there's also no reason to declare that DT should be the only way to
boot a platform.
There is also no need to use UEFI for
booting a 64 bit kernel
Correct. However, it can provide a more familiar user experience and
tends to be better supported. For instance, I'm not sure you can get a
full graphical GRUB menu from the other solutions (but I haven't really
investigated).
In case this is your impression, it's not because I am contributing to
the UEFI that I am advocating UEFI as the "one true way" to boot a platform.
My experience however is that it may make it easier for end-users to run
and keep a distro updated, especially when modern Linux distros support
ESPs and EFI GRUB as a means to customize boot options, such as the
ability to select kernels or provide kernel options through a GUI, as is
the case on an x86 PC.
But again, we're not pitting one boot method against one another. We're
only providing some options and it's up to the users to choose which
method they think suits them best.
OP specifically pointed to the UEFI firmware, and since I'm somewhat
familiar with it, I tried to provide some info on that.
> Do you have a pointer to what the issues with USB and DMA are?
Devices that sit behind the GPU/Videocore can only access 1 GB, and
require a translation, and (from what we gather) there happens to be a
silicon bug that forces devices that don't sit behind GPU (USB, Genet)
to limit DMA to 3 GB. There is also non-cache coherency for XHCI over
PCIe and some weird ECAM, if I recall correctly.
Some of these are also mentioned on lkml such as in:
https://lkml.org/lkml/2019/9/6/352
Regards,
/Pete
Reply to: