Re: [PATCH v3 4/4] ARM: vfp: Reimplement VFP exception entry in C code

[Linus Walleij <linus.walleij@linaro.org>]

On Thu, Mar 16, 2023 at 9:20 AM Ard Biesheuvel <ardb@kernel.org> wrote:

> En/disabling softirqs from asm code turned out to be trickier than
> expected, so vfp_support_entry now returns by tail calling
> __local_enable_bh_ip() and passing the same arguments that a C call to
> local_bh_enable() would pass. However, this is slightly hacky, as we
> don't want to carry our own implementation of local_bh_enable().
>
> So let's bite the bullet, and get rid of the asm logic in
> vfp_support_entry that reasons about whether or not to save and/or
> reload the VFP state, and about whether or not an FP exception is
> pending, and only keep the VFP loading logic as a function that is
> callable from C.
>
> Replicate the removed logic in vfp_entry(), and use the exact same
> reasoning as in the asm code. To emphasize the correspondance, retain
> some of the asm comments in the C version as well.
>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

I tried to model what the assembly is doing in my head to review
if the new code in C does the same thing, but after following some of
the semantics (which look correct) I realized it will mostly be down to
testing anyway.

It's definately better to have it like this so FWIW:
Acked-by: Linus Walleij <linus.walleij@linaro.org>

Apparently a bunch of this code was written by Catalin for VFPv3 support,
he may or may not have the memory and time to go back and look at it, but
let's page him in anyway :)

Yours,
Linus Walleij

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