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    Subject[PATCH] drm: amd: dc: don't use FP math when Kcov is enabled
    Date
    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
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