[PATCH] drm/amd/display: Fix warning about overflow

[Christian König]

Am 13.10.2017 um 10:08 schrieb Michel Dänzer:
> On 12/10/17 07:54 PM, Harry Wentland wrote:
>> We're overflowing the last bit. Cast it explicitly
>>
>> Signed-off-by: Harry Wentland <harry.wentland at amd.com>
>> ---
>>   drivers/gpu/drm/amd/display/dc/bios/bios_parser2.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/amd/display/dc/bios/bios_parser2.c b/drivers/gpu/drm/amd/display/dc/bios/bios_parser2.c
>> index cb94e18cc455..715dc789bb24 100644
>> --- a/drivers/gpu/drm/amd/display/dc/bios/bios_parser2.c
>> +++ b/drivers/gpu/drm/amd/display/dc/bios/bios_parser2.c
>> @@ -1047,7 +1047,7 @@ static enum bp_result get_embedded_panel_info_v2_1(
>>   		lvds->lcd_timing.miscinfo & ATOM_V_REPLICATIONBY2;
>>   	info->lcd_timing.misc_info.COMPOSITE_SYNC =
>>   		lvds->lcd_timing.miscinfo & ATOM_COMPOSITESYNC;
>> -	info->lcd_timing.misc_info.INTERLACE =
>> +	info->lcd_timing.misc_info.INTERLACE = (uint32_t)
>>   		lvds->lcd_timing.miscinfo & ATOM_INTERLACE;
> I wasn't sure offhand, so I had to write a little test program, but it 
> looks like this doesn't work as intended: (lvds->lcd_timing.miscinfo & 
> ATOM_INTERLACE) is an unsigned 16-bit value, which is either 0x80 
> (ATOM_INTERLACE) or 0. Assigning that to the unsigned 1-bit field 
> info->lcd_timing.misc_info.INTERLACE always results in 0. Casting the 
> 16-bit value to 32 bits doesn't change that. I think what's intended 
> here is something like info->lcd_timing.misc_info.INTERLACE = 
> (lvds->lcd_timing.miscinfo & ATOM_INTERLACE) != 0; Looks like there's 
> the same problem with other fields of info->lcd_timing.misc_info 
> above. Another possible solution is making the fields of struct 
> misc_info bool instead of uint32_t.

While your approach works as well IIRC converting an arbitrary value 
into a boolean is usually done with "!!".

E.g. that should look like:

     info->lcd_timing.misc_info.INTERLACE =
         !!(lvds->lcd_timing.miscinfo & ATOM_INTERLACE);

Regards,
Christian.