linux-kernel - Re: Stack-frame warnings in display_mode_vba

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Date:   Fri, 29 Jul 2022 22:12:38 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     André Almeida <andrealmeid@...lia.com>
Cc:     sfr@...b.auug.org.au, harry.wentland@....com, sunpeng.li@....com,
        arnd@...db.de, alexander.deucher@....com, linux@...ck-us.net,
        linux-next@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        amd-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: Stack-frame warnings in display_mode_vba_32.c

On Fri, Jul 29, 2022 at 11:41:55PM -0300, André Almeida wrote:
> Hi Paul,
> 
> Às 23:25 de 29/07/22, Paul E. McKenney escreveu:
> > Hello!
> > 
> > I am seeing the following in allmodconfig builds of recent -next on x86:
> > 
> > drivers/gpu/drm/amd/amdgpu/../display/dc/dml/dcn32/display_mode_vba_32.c: In function ‘DISPCLKDPPCLKDCFCLKDeepSleepPrefetchParametersWatermarksAndPerformanceCalculation’:
> > drivers/gpu/drm/amd/amdgpu/../display/dc/dml/dcn32/display_mode_vba_32.c:1659:1: error: the frame size of 2144 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]
> >  1659 | }
> >       | ^
> > drivers/gpu/drm/amd/amdgpu/../display/dc/dml/dcn32/display_mode_vba_32.c: In function ‘dml32_ModeSupportAndSystemConfigurationFull’:
> > drivers/gpu/drm/amd/amdgpu/../display/dc/dml/dcn32/display_mode_vba_32.c:3799:1: error: the frame size of 2480 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]
> >  3799 | } // ModeSupportAndSystemConfigurationFull
> >       | ^
> 
> I think they are fixed at amd-staging-drm-next:
> 
> git log --oneline amd/amd-staging-drm-next
> drivers/gpu/drm/amd/display/dc/dml/dcn32/display_mode_vba_32.c
> 953daa61981b drm/amd/display: Reduce stack size in the mode support function
> 361e705e712d drm/amd/display: reduce stack for
> dml32_CalculatePrefetchSchedule
> f2dbf5a4dd1e drm/amd/display: reduce stack for
> dml32_CalculateWatermarksMALLUseAndDRAMSpeedChangeSupport
> a0a68cda2ef8 drm/amd/display: reduce stack for dml32_CalculateVMRowAndSwath
> ca6730ca0f01 drm/amd/display: reduce stack for
> dml32_CalculateSwathAndDETConfiguration
> 593eef8c1a5e drm/amd/display: reduce stack size in dcn32 dml (v2)
> 
> https://gitlab.freedesktop.org/agd5f/linux/-/commits/amd-staging-drm-next/drivers/gpu/drm/amd/display/dc/dml/dcn32/display_mode_vba_32.c

Very good, thank you!  I will test again on the next -next.

							Thanx, Paul

> > Bisection located the commit shown below.  Doing an allmodconfig build
> > on this commit reproduces the error, its parent builds fine.
> > 
> > Thoughts?
> > 
> > 							Thanx, Paul
> > 
> > ------------------------------------------------------------------------
> > 
> > commit 3876a8b5e241081b2a519f848a65c00d8e6cd124
> > Author: Guenter Roeck <linux@...ck-us.net>
> > Date:   Tue Jul 12 15:42:47 2022 -0700
> > 
> >     drm/amd/display: Enable building new display engine with KCOV enabled
> >     
> >     The new display engine uses floating point math, which is not supported
> >     by KCOV. Commit 9d1d02ff3678 ("drm/amd/display: Don't build DCN1 when kcov
> >     is enabled") tried to work around the problem by disabling
> >     CONFIG_DRM_AMD_DC_DCN if KCOV_INSTRUMENT_ALL and KCOV_ENABLE_COMPARISONS
> >     are enabled. The result is that KCOV can not be enabled on systems which
> >     require this display engine. A much simpler and less invasive solution is
> >     to disable KCOV selectively when compiling the display enagine while
> >     keeping it enabled for the rest of the kernel.
> >     
> >     Fixes: 9d1d02ff3678 ("drm/amd/display: Don't build DCN1 when kcov is enabled")
> >     Cc: Arnd Bergmann <arnd@...db.de>
> >     Cc: Leo Li <sunpeng.li@....com>
> >     Reviewed-by: Harry Wentland <harry.wentland@....com>
> >     Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> >     Signed-off-by: Alex Deucher <alexander.deucher@....com>
> > 
> > diff --git a/drivers/gpu/drm/amd/display/Kconfig b/drivers/gpu/drm/amd/display/Kconfig
> > index b4029c0d5d8c5..96cbc87f7b6b8 100644
> > --- a/drivers/gpu/drm/amd/display/Kconfig
> > +++ b/drivers/gpu/drm/amd/display/Kconfig
> > @@ -6,7 +6,7 @@ config DRM_AMD_DC
> >  	bool "AMD DC - Enable new display engine"
> >  	default y
> >  	select SND_HDA_COMPONENT if SND_HDA_CORE
> > -	select DRM_AMD_DC_DCN if (X86 || PPC64) && !(KCOV_INSTRUMENT_ALL && KCOV_ENABLE_COMPARISONS)
> > +	select DRM_AMD_DC_DCN if (X86 || PPC64)
> >  	help
> >  	  Choose this option if you want to use the new display engine
> >  	  support for AMDGPU. This adds required support for Vega and
> > diff --git a/drivers/gpu/drm/amd/display/dc/Makefile b/drivers/gpu/drm/amd/display/dc/Makefile
> > index 273f8f2c8e020..b9effadfc4bb7 100644
> > --- a/drivers/gpu/drm/amd/display/dc/Makefile
> > +++ b/drivers/gpu/drm/amd/display/dc/Makefile
> > @@ -25,6 +25,9 @@
> >  DC_LIBS = basics bios dml clk_mgr dce gpio irq link virtual
> >  
> >  ifdef CONFIG_DRM_AMD_DC_DCN
> > +
> > +KCOV_INSTRUMENT := n
> > +
> >  DC_LIBS += dcn20
> >  DC_LIBS += dsc
> >  DC_LIBS += dcn10