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Re: [PATCH v2] mips/malta: pass RNG seed to to kernel via env var

From: Jason A. Donenfeld
Subject: Re: [PATCH v2] mips/malta: pass RNG seed to to kernel via env var
Date: Tue, 4 Oct 2022 13:10:20 +0200

On Tue, Oct 4, 2022 at 1:03 PM Peter Maydell <peter.maydell@linaro.org> wrote:
> What I'm asking, I guess, is why you're messing with this board
> model at all if you haven't added this functionality to u-boot.
> This is just an emulation of an ancient bit of MIPS hardware, which
> nobody really cares about very much I hope.

I think most people emulating MIPS would disagree. This is basically a
reference platform for most intents and purposes. As I mentioned, this
involves `-kernel` -- the thing that's used when you explicitly opt-in
to not using a bootloader, so when you sign up for QEMU arranging the
kernel image and its environment. Neglecting to pass an RNG seed would
be a grave mistake.

> I'm not saying this is a bad patch -- I'm just saying that
> QEMU should not be in the business of defining bootloader-to-kernel
> interfaces if it can avoid it, so usually the expectation is
> that we are just implementing interfaces that are already
> defined, documented and implemented by a real bootloader and kernel.

Except that's not really the way things have ever worked here. The
kernel now has the "rngseed" env var functionality, which is useful
for a variety of scenarios -- kexec, firmware, and *most importantly*
for QEMU. Don't block progress here.

> -kernel generally means "emulate the platform's boot loader"

And here, a platform bootloader could pass this, just as is the case
with m68k's BI_RNG_SEED or x86's setup_data RNG SEED or device tree's
rng-seed or EFI's LINUX_EFI_RANDOM_SEED_TABLE_GUID or MIPS' "rngseed"
fw environment variable. These are important facilities to have.
Bootloaders and hypervisors alike must implement them. *Do not block
progress here.*


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