From: Arnd Bergmann <arnd@arndb.de>
To: Alex Deucher <alexander.deucher@amd.com>,
        =?UTF-8?q?Christian=20K=C3=B6nig?= <christian.koenig@amd.com>
Cc: Arnd Bergmann <arnd@arndb.de>, David Airlie <airlied@linux.ie>,
        Harry Wentland <harry.wentland@amd.com>,
        Jordan Lazare <Jordan.Lazare@amd.com>, Roman Li <Roman.Li@amd.com>,
        Shirish S <shirish.s@amd.com>, amd-gfx@lists.freedesktop.org,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Subject: [PATCH] drm: amd: dc: don't use FP math when Kcov is enabled
Date: Mon,  4 Dec 2017 14:08:19 +0100
Message-Id: <20171204131031.1418828-1-arnd@arndb.de>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 7599
Lines: 102

Building the DCN 1.0 Raven display driver with CONFIG_KCOV_INSTRUMENT_ALL=y
and CONFIG_KCOV_ENABLE_COMPARISONS=y results in warnings about many functions
that do a comparison of floating-point variables:

drivers/gpu/drm/amd/display/dc/calcs/dcn_calcs.o: In function `dcn_bw_calc_rq_dlg_ttu':
dcn_calcs.c:(.text+0x263): undefined reference to `__sanitizer_cov_trace_cmpf'
drivers/gpu/drm/amd/display/dc/calcs/dcn_calcs.o: In function `hack_force_pipe_split':
dcn_calcs.c:(.text+0x155b): undefined reference to `__sanitizer_cov_trace_cmpf'
drivers/gpu/drm/amd/display/dc/calcs/dcn_calcs.o: In function `dcn_find_dcfclk_suits_all':
dcn_calcs.c:(.text+0x190e): undefined reference to `__sanitizer_cov_trace_cmpf'
drivers/gpu/drm/amd/display/dc/calcs/dcn_calcs.o: In function `dcn_validate_bandwidth':
dcn_calcs.c:(.text+0xe121): undefined reference to `__sanitizer_cov_trace_cmpd'
drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_math.o: In function `dcn_bw_mod':
dcn_calc_math.c:(.text+0x22): undefined reference to `__sanitizer_cov_trace_cmpf'
drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_math.o: In function `dcn_bw_min2':
dcn_calc_math.c:(.text+0xb2): undefined reference to `__sanitizer_cov_trace_cmpf'
drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_math.o: In function `dcn_bw_ceil2':
dcn_calc_math.c:(.text+0x2a0): undefined reference to `__sanitizer_cov_trace_cmpd'
drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_math.o: In function `dcn_bw_max3':
dcn_calc_math.c:(.text+0x325): undefined reference to `__sanitizer_cov_trace_cmpf'
drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_math.o: In function `dcn_bw_max5':
dcn_calc_math.c:(.text+0x3c3): undefined reference to `__sanitizer_cov_trace_cmpf'
drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_math.o: In function `dcn_bw_log':
dcn_calc_math.c:(.text+0x54e): undefined reference to `__sanitizer_cov_trace_cmpd'
dcn_calc_math.c:(.text+0x57c): undefined reference to `__sanitizer_cov_trace_cmpd'
drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_auto.o: In function `scaler_settings_calculation':
dcn_calc_auto.c:(.text+0x5c5): undefined reference to `__sanitizer_cov_trace_cmpf'
drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_auto.o: In function `mode_support_and_system_configuration':
dcn_calc_auto.c:(.text+0x137c): undefined reference to `__sanitizer_cov_trace_cmpd'
drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_auto.o: In function `mode_support_and_system_configuration':
dcn_calc_auto.c:(.text+0x9233): undefined reference to `__sanitizer_cov_trace_cmpd'
drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_auto.o: In function `mode_support_and_system_configuration':
dcn_calc_auto.c:(.text+0xb70f): undefined reference to `__sanitizer_cov_trace_cmpd'
drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_auto.o: In function `mode_support_and_system_configuration':
dcn_calc_auto.c:(.text+0x121fd): undefined reference to `__sanitizer_cov_trace_cmpd'
drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_auto.o: In function `display_pipe_configuration':
dcn_calc_auto.c:(.text+0x15a2f): undefined reference to `__sanitizer_cov_trace_cmpd'
drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_auto.o: In function `dispclkdppclkdcfclk_deep_sleep_prefetch_parameters_watermarks_and_performance_calculation':
dcn_calc_auto.c:(.text+0x17c2d): undefined reference to `__sanitizer_cov_trace_cmpf'
drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_auto.o: In function `dispclkdppclkdcfclk_deep_sleep_prefetch_parameters_watermarks_and_performance_calculation':
dcn_calc_auto.c:(.text+0x19362): undefined reference to `__sanitizer_cov_trace_cmpd'
drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_auto.o: In function `dispclkdppclkdcfclk_deep_sleep_prefetch_parameters_watermarks_and_performance_calculation':
dcn_calc_auto.c:(.text+0x25575): undefined reference to `__sanitizer_cov_trace_cmpd'
drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_auto.o: In function `dispclkdppclkdcfclk_deep_sleep_prefetch_parameters_watermarks_and_performance_calculation':
dcn_calc_auto.c:(.text+0x27f33): undefined reference to `__sanitizer_cov_trace_cmpd'
drivers/gpu/drm/amd/display/dc/dml/display_rq_dlg_calc.o: In function `get_refcyc_per_delivery':
display_rq_dlg_calc.c:(.text+0xb5): undefined reference to `__sanitizer_cov_trace_cmpd'
drivers/gpu/drm/amd/display/dc/dml/display_rq_dlg_calc.o: In function `calculate_ttu_cursor.isra.1':
display_rq_dlg_calc.c:(.text+0x9f6): undefined reference to `__sanitizer_cov_trace_cmpd'
drivers/gpu/drm/amd/display/dc/dml/display_rq_dlg_calc.o: In function `dml_rq_dlg_get_dlg_params':
display_rq_dlg_calc.c:(.text+0x82cc): undefined reference to `__sanitizer_cov_trace_cmpf'
drivers/gpu/drm/amd/display/dc/dml/dml1_display_rq_dlg_calc.o: In function `get_refcyc_per_delivery.isra.0':
dml1_display_rq_dlg_calc.c:(.text+0x6c4): undefined reference to `__sanitizer_cov_trace_cmpd'
drivers/gpu/drm/amd/display/dc/dml/dml1_display_rq_dlg_calc.o: In function `get_vratio_pre.isra.2':
dml1_display_rq_dlg_calc.c:(.text+0x957): undefined reference to `__sanitizer_cov_trace_cmpd'
drivers/gpu/drm/amd/display/dc/dml/dml1_display_rq_dlg_calc.o: In function `get_swath_need.isra.3':
dml1_display_rq_dlg_calc.c:(.text+0xc8e): undefined reference to `__sanitizer_cov_trace_cmpf'
drivers/gpu/drm/amd/display/dc/dml/dml1_display_rq_dlg_calc.o: In function `dml1_extract_rq_regs':
dml1_display_rq_dlg_calc.c:(.text+0x30a8): undefined reference to `__sanitizer_cov_trace_cmpd'
drivers/gpu/drm/amd/display/dc/dml/dml1_display_rq_dlg_calc.o: In function `dml1_rq_dlg_get_dlg_params':
dml1_display_rq_dlg_calc.c:(.text+0x41ee): undefined reference to `__sanitizer_cov_trace_cmpd'
drivers/gpu/drm/amd/display/dc/dml/dml1_display_rq_dlg_calc.o: In function `dml1_rq_dlg_get_dlg_params':
dml1_display_rq_dlg_calc.c:(.text+0x8f95): undefined reference to `__sanitizer_cov_trace_cmpf'
drivers/gpu/drm/amd/display/dc/dml/dml_common_defs.o: In function `dml_round':
dml_common_defs.c:(.text+0x77): undefined reference to `__sanitizer_cov_trace_cmpd'
drivers/gpu/drm/amd/display/dc/dml/display_mode_vba.o: In function `adjust_ReturnBW':
display_mode_vba.c:(.text+0x4490): undefined reference to `__sanitizer_cov_trace_cmpd'

We already prevent the driver from being built on non-x86 architectures
because of its use of floating-point arithmetic, this extends the
dependency to also cover Kcov-enabled builds, which arguably is a much
more severe limitation.

I tried implementing the two functions in KCOV: __sanitizer_cov_trace_cmpd
and __sanitizer_cov_trace_cmpf, but that fails to build on architectures
that do not support any floating-point functions, or would require making
that code x86 specific as well.  I also looked at what it would take to
convert the code to fixed-point arithmetic, but quickly gave up. This
is probably the right approach, but it requires a non-trivial amount of
work and certainly won't be appropriate as a bugfix.

Fixes: bf2e2e2e0ea9 ("drm/amd/display: Limit DCN to x86 arch")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/gpu/drm/amd/display/Kconfig | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/Kconfig b/drivers/gpu/drm/amd/display/Kconfig
index ec3285f65517..5cd5906c9bee 100644
--- a/drivers/gpu/drm/amd/display/Kconfig
+++ b/drivers/gpu/drm/amd/display/Kconfig
@@ -30,6 +30,8 @@ config DRM_AMD_DC_FBC
 config DRM_AMD_DC_DCN1_0
 	bool "DCN 1.0 Raven family"
 	depends on DRM_AMD_DC && X86
+	# x86 floating point math here breaks with KCOV:
+	depends on !(KCOV_INSTRUMENT_ALL && KCOV_ENABLE_COMPARISONS) || BROKEN
 	help
 	  Choose this option if you want to have
 	  RV family for display engine
-- 
2.9.0