[PATCH] drm/amd/display: Revert "add DCN support for aarch64"

[Alex Deucher]

On Tue, Dec 29, 2020 at 8:17 AM Ard Biesheuvel <ardb at kernel.org> wrote:
>
> On Wed, 16 Dec 2020 at 23:26, Ard Biesheuvel <ardb at kernel.org> wrote:
> >
> > On Wed, 16 Dec 2020 at 19:00, Alex Deucher <alexdeucher at gmail.com> wrote:
> > >
> > > On Mon, Dec 14, 2020 at 12:53 PM Ard Biesheuvel <ardb at kernel.org> wrote:
> > > >
> > > > This reverts commit c38d444e44badc557cf29fdfdfb823604890ccfa.
> > > >
> > > > Simply disabling -mgeneral-regs-only left and right is risky, given that
> > > > the standard AArch64 ABI permits the use of FP/SIMD registers anywhere,
> > > > and GCC is known to use SIMD registers for spilling, and may invent
> > > > other uses of the FP/SIMD register file that have nothing to do with the
> > > > floating point code in question. Note that putting kernel_neon_begin()
> > > > and kernel_neon_end() around the code that does use FP is not sufficient
> > > > here, the problem is in all the other code that may be emitted with
> > > > references to SIMD registers in it.
> > > >
> > > > So the only way to do this properly is to put all floating point code in
> > > > a separate compilation unit, and only compile that unit with
> > > > -mgeneral-regs-only. But perhaps the use of floating point here is
> > > > something that should be reconsidered entirely.
> > > >
> > > > Cc: Catalin Marinas <catalin.marinas at arm.com>
> > > > Cc: Will Deacon <will at kernel.org>
> > > > Cc: Dave Martin <dave.martin at arm.com>
> > > > Cc: Rob Herring <robh at kernel.org>
> > > > Cc: Leo Li <sunpeng.li at amd.com>
> > > > Cc: Alex Deucher <alexander.deucher at amd.com>
> > > > Cc: "Christian König" <christian.koenig at amd.com>
> > > > Cc: David Airlie <airlied at linux.ie>
> > > > Cc: Daniel Vetter <daniel at ffwll.ch>
> > > > Cc: Daniel Kolesa <daniel at octaforge.org>
> > > > Cc: amd-gfx at lists.freedesktop.org
> > > > Cc: dri-devel at lists.freedesktop.org
> > > > Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
> > >
> > > Can rebase this on Linus' master branch?  There were a number of new
> > > asics added which copy pasted the ARM64 support.
> > >
> >
> > Not sure what you are asking me here. Reverting commit c38d444e44badc5
> > on top of mainline is not going to fix the other code that was added.
> > Or are you asking me to go and find the patches (how many?) that added
> > new ASICs and fix them for arm64?
> >
> > Note that this code is critically broken, as it may corrupt user
> > process state arbitrarily. So if new code was added that contains the
> > same bug, it should be reverted so that the respective authors can fix
> > it and resubmit.
> >
>
> Is this simply about dropping the newly added references to
> $(dml_rcflags) from the Makefile? Because that is quite trivial ...

Yes, I was thinking something like the attached patch.

Alex
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