linux-kernel - Stack-frame warnings in display_mode_vba

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Message-ID: <20220730022532.GA1234397@paulmck-ThinkPad-P17-Gen-1>
Date:   Fri, 29 Jul 2022 19:25:32 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     linux@...ck-us.net, alexander.deucher@....com, arnd@...db.de,
        sunpeng.li@....com, harry.wentland@....com
Cc:     sfr@...b.auug.org.au, linux-next@...r.kernel.org,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Stack-frame warnings in display_mode_vba_32.c

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
      | ^

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