On Wed, Jan 20, 2021 at 3:20 AM Ard Biesheuvel [off-list ref] wrote:

On Tue, 5 Jan 2021 at 17:23, Alex Deucher [off-list ref] wrote:

quoted

On Tue, Jan 5, 2021 at 8:05 AM Will Deacon [off-list ref] wrote:

quoted

On Mon, Jan 04, 2021 at 11:27:24AM -0500, Alex Deucher wrote:

quoted

On Tue, Dec 29, 2020 at 8:17 AM Ard Biesheuvel [off-list ref] wrote:

quoted

On Wed, 16 Dec 2020 at 23:26, Ard Biesheuvel [off-list ref] wrote:

quoted

On Wed, 16 Dec 2020 at 19:00, Alex Deucher [off-list ref] wrote:

quoted

On Mon, Dec 14, 2020 at 12:53 PM Ard Biesheuvel [off-list ref] wrote:

quoted

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@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Dave Martin <dave.martin@arm.com>
Cc: Rob Herring <robh@kernel.org>
Cc: Leo Li <sunpeng.li@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: David Airlie <redacted>
Cc: Daniel Vetter <redacted>
Cc: Daniel Kolesa <redacted>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Ard Biesheuvel <ardb@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

quoted

From fbc93ca7d7739861ce63f6b483cf23d7cf1d69fb Mon Sep 17 00:00:00 2001
From: Alex Deucher <alexander.deucher@amd.com>
Date: Mon, 4 Jan 2021 11:24:20 -0500
Subject: [PATCH] drm/amdgpu/display: drop DCN support for aarch64

From Ard:

"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."

Disable support until the code can be properly refactored to support this
properly on aarch64.

Reported-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
---
 drivers/gpu/drm/amd/display/Kconfig           |  2 +-
 drivers/gpu/drm/amd/display/dc/calcs/Makefile |  4 ----
 .../gpu/drm/amd/display/dc/clk_mgr/Makefile   | 21 -------------------
 drivers/gpu/drm/amd/display/dc/dcn10/Makefile |  7 -------
 .../drm/amd/display/dc/dcn10/dcn10_resource.c |  7 -------
 drivers/gpu/drm/amd/display/dc/dcn20/Makefile |  4 ----
 drivers/gpu/drm/amd/display/dc/dcn21/Makefile |  4 ----
 drivers/gpu/drm/amd/display/dc/dcn30/Makefile |  5 -----
 .../gpu/drm/amd/display/dc/dcn301/Makefile    |  4 ----
 .../gpu/drm/amd/display/dc/dcn302/Makefile    |  4 ----
 drivers/gpu/drm/amd/display/dc/dml/Makefile   |  4 ----
 drivers/gpu/drm/amd/display/dc/dsc/Makefile   |  4 ----
 drivers/gpu/drm/amd/display/dc/os_types.h     |  4 ----
 13 files changed, 1 insertion(+), 73 deletions(-)

Acked-by: Will Deacon <will@kernel.org>

Applied.  Thanks!

It appears your version of the revert does not apply cleanly to v5.10,
so now we're stuck with this broken AArch64 support in a LTS kernel.

Any objections to taking my original revert into v5.10 as a special backport?

No concerns, please go ahead.
Acked-by: Alex Deucher <alexander.deucher@amd.com>
if you want to send it to stable.

Alex

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