Re: [PATCH] drm/amd/display: Add missing hard-float compile flags for PPC64 builds

[Guenter Roeck]

On 7/14/22 11:49, Melissa Wen wrote:
> O 07/13, Alex Deucher wrote:
> > On Wed, Jul 13, 2022 at 7:09 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > > On Wed, Jul 13, 2022 at 05:20:40PM -0400, Alex Deucher wrote:
> > > > > The problem is not the FPU operations, but the fact that soft-float
> > > > > and hard-float compiled code is linked together. The soft-float and
> > > > > hard-float ABIs on powerpc are not compatible, so one ends up with
> > > > > an object file which is partially soft-float and partially hard-float
> > > > > compiled and thus uses different ABIs. That can only create chaos,
> > > > > so the linker complains about it.
> > > >
> > > > I get that, I just don't see why only DCN 3.1.x files have this
> > > > problem.  The DCN 2.x files should as well.
> > >
> > > Seen in drivers/gpu/drm/amd/display/dc/clk_mgr/Makefile:
> > >
> > > # prevent build errors regarding soft-float vs hard-float FP ABI tags
> > > # this code is currently unused on ppc64, as it applies to Renoir APUs only
> > > ifdef CONFIG_PPC64
> > > CFLAGS_$(AMDDALPATH)/dc/clk_mgr/dcn21/rn_clk_mgr.o := $(call cc-option,-mno-gnu-attribute)
> > > endif
> > >
> > > Does that explain it ?
> >
> > I would expect to see it in dcn20_resource.c and dcn30_clk_mgr.c for
> > example.  They follow the same pattern as the dcn 3.1.x files.  They
> > call functions that use FP, but maybe there is some FP code still in
> > those functions that we missed somehow.
>
> Hi,
>
> I'm a little late here, but I'm not able to reproduce the issue yet.
> I have this setup:
> - gcc 11.3.0
> - binutils 2.38.50
> - mainline kernel (torvalds) version: 5.19.0-rc6 (cross-compiling)
>    -> make ARCH=powerpc CROSS_COMPILE=powerpc64-linux-gnu- allmodconfig
>      => DRM_AMD_DC [=y] && HAS_IOMEM [=y] && DRM [=m] && DRM_AMDGPU [=m] && (X86 || PPC64 [=y]) && (!KCOV_INSTRUMENT_ALL [=n] || !KCOV_ENABLE_COMPARISONS [=n])
>    -> make -j16 ARCH=powerpc CROSS_COMPILE=powerpc64-linux-gnu-
>
> Am I missing something?
>
> So, as Alex mentioned the possibility of some non-isolated FPU code in
> 3.1, I reviewed dcn31 code and my best bet so far is that the issue
> is here:
>
> https://github.com/torvalds/linux/blob/master/drivers/gpu/drm/amd/display/dc/dcn31/dcn31_resource.c#L1721
>
> Although dcn31_update_soc_for_wm_a() is only called inside
> dml/dcn31/dcn31_fpu:
> - dc->res_pool->funcs->update_soc_for_wm_a(dc, context);
>
> it's declared in dcn31_resource and has FPU code. So, we should move it
> to dml/dcn31/dcn31_fpu.
>
> However, as I can't reproduce the issue, I don't know if it addresses
> the problem reported here and also if everything will be clean after
> moving it.

I don't think that would solve anything. As I have tried to point out,
the problem is that code compiled with hard-float is linked together
with code compiled with soft-float. An alternate fix might be something
like the one attached below, but I don't know if that would be correct
and/or complete.

> Guenter,
>
> Can you provide more info about your setup: cross-compile or not, any
> flags, branch, etc?

Nothing special. Same compile options as the ones you use, and it is a
cross-compile environment. I tried gcc 11.2.0 with binutils 2.36.1
and gcc 11.3.0 with binutils 2.38.

Guenter

---
diff --git a/drivers/gpu/drm/amd/display/dc/dcn31/Makefile b/drivers/gpu/drm/amd/display/dc/dcn31/Makefile
index ec041e3cda30..44ff6f196860 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn31/Makefile
+++ b/drivers/gpu/drm/amd/display/dc/dcn31/Makefile
@@ -10,6 +10,8 @@
 #
 # Makefile for dcn31.

+CFLAGS_$(AMDDALPATH)/dc/dcn31/dcn31_resource.o := $(call cc-option,-mno-gnu-attribute)
+
 DCN31 = dcn31_resource.o dcn31_hubbub.o dcn31_hwseq.o dcn31_init.o dcn31_hubp.o \
        dcn31_dccg.o dcn31_optc.o dcn31_dio_link_encoder.o dcn31_panel_cntl.o \
        dcn31_apg.o dcn31_hpo_dp_stream_encoder.o dcn31_hpo_dp_link_encoder.o \
diff --git a/drivers/gpu/drm/amd/display/dc/dcn315/Makefile b/drivers/gpu/drm/amd/display/dc/dcn315/Makefile
index 59381d24800b..55fcae2d2aae 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn315/Makefile
+++ b/drivers/gpu/drm/amd/display/dc/dcn315/Makefile
@@ -25,6 +25,8 @@

 DCN315 = dcn315_resource.o

+CFLAGS_$(AMDDALPATH)/dc/dcn315/$(DCN315) := $(call cc-option,-mno-gnu-attribute)
+
 AMD_DAL_DCN315 = $(addprefix $(AMDDALPATH)/dc/dcn315/,$(DCN315))

 AMD_DISPLAY_FILES += $(AMD_DAL_DCN315)
diff --git a/drivers/gpu/drm/amd/display/dc/dcn316/Makefile b/drivers/gpu/drm/amd/display/dc/dcn316/Makefile
index 819d44a9439b..7251ef9c1afb 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn316/Makefile
+++ b/drivers/gpu/drm/amd/display/dc/dcn316/Makefile
@@ -25,6 +25,8 @@

 DCN316 = dcn316_resource.o

+CFLAGS_$(AMDDALPATH)/dc/dcn316/$(DCN316) := $(call cc-option,-mno-gnu-attribute)
+
 AMD_DAL_DCN316 = $(addprefix $(AMDDALPATH)/dc/dcn316/,$(DCN316))

 AMD_DISPLAY_FILES += $(AMD_DAL_DCN316)