• Takashi Sakamoto's avatar
    ASoC: hdmi-codec: use unsigned type to structure members with bit-field · 9e4d59ad
    Takashi Sakamoto authored
    This is a fix for Linux 4.10-rc1.
    
    In C language specification, a bit-field is interpreted as a signed or
    unsigned integer type consisting of the specified number of bits.
    
    In GCC manual, the range of a signed bit field of N bits is from
    -(2^N) / 2 to ((2^N) / 2) - 1
    https://www.gnu.org/software/gnu-c-manual/gnu-c-manual.html#Bit-Fields
    
    Therefore, when defined as 1 bit-field with signed type, variables can
    represents -1 and 0.
    
    The snd-soc-hdmi-codec module includes a structure which has signed type
    members with bit-fields. Codes of this module assign 0 and 1 to the
    members. This seems to result in implementation-dependent behaviours.
    
    As of v4.10-rc1 merge window, outside of sound subsystem, this structure
    is referred by below GPU modules.
     - tda998x
     - sti-drm
     - mediatek-drm-hdmi
     - msm
    
    As long as I review their codes relevant to the structure, the structure
    members are used just for condition statements and printk formats.
    My proposal of change is a bit intrusive to the printk formats but this
    may be acceptable.
    
    Totally, it's reasonable to use unsigned type for the structure members.
    This bug is detected by Sparse, static code analyzer with below warnings.
    
    ./include/sound/hdmi-codec.h:39:26: error: dubious one-bit signed bitfield
    ./include/sound/hdmi-codec.h:40:28: error: dubious one-bit signed bitfield
    ./include/sound/hdmi-codec.h:41:29: error: dubious one-bit signed bitfield
    ./include/sound/hdmi-codec.h:42:31: error: dubious one-bit signed bitfield
    
    Fixes: 09184118 ("ASoC: hdmi-codec: Add hdmi-codec for external HDMI-encoders")
    Signed-off-by: default avatarTakashi Sakamoto <o-takashi@sakamocchi.jp>
    Acked-by: default avatarArnaud Pouliquen <arnaud.pouliquen@st.com>
    Signed-off-by: default avatarMark Brown <broonie@kernel.org>
    CC: stable@vger.kernel.org
    9e4d59ad
hdmi-codec.h 2.24 KB