Re: [PATCH] drm/panel: himax-hx8279: Initialize goa_{even,odd}_valid in hx8279_check_goa_config()

[Neil Armstrong <neil.armstrong@linaro.org>]

On 23/04/2025 15:45, Neil Armstrong wrote:
> On 22/04/2025 23:20, Nathan Chancellor wrote:
>> Clang warns (or errors with CONFIG_WERROR=y):
>>
>>    drivers/gpu/drm/panel/panel-himax-hx8279.c:838:6: error: variable 'goa_even_valid' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
>>      838 |         if (num_zero == ARRAY_SIZE(desc->goa_even_timing))
>>          |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>    drivers/gpu/drm/panel/panel-himax-hx8279.c:842:23: note: uninitialized use occurs here
>>      842 |         if (goa_odd_valid != goa_even_valid)
>>          |                              ^~~~~~~~~~~~~~
>>    drivers/gpu/drm/panel/panel-himax-hx8279.c:838:2: note: remove the 'if' if its condition is always true
>>      838 |         if (num_zero == ARRAY_SIZE(desc->goa_even_timing))
>>          |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>      839 |                 goa_even_valid = false;
>>    drivers/gpu/drm/panel/panel-himax-hx8279.c:818:36: note: initialize the variable 'goa_even_valid' to silence this warning
>>      818 |         bool goa_odd_valid, goa_even_valid;
>>          |                                           ^
>>          |                                            = 0
>>
>> Even though only the even valid variable gets flagged, both valid
>> variables appear to have the same issue of possibly being used
>> uninitialized if the if statement initializing them to false is not
>> taken.
>>
>> Initialize both values to true to clear up the warning and remove any
>> possibility of encountering undefined behavior.
>>
>> Fixes: 38d42c261389 ("drm: panel: Add driver for Himax HX8279 DDIC panels")
>> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
>> ---
>>   drivers/gpu/drm/panel/panel-himax-hx8279.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/panel/panel-himax-hx8279.c b/drivers/gpu/drm/panel/panel-himax-hx8279.c
>> index b48b350b62da..92f351e66c25 100644
>> --- a/drivers/gpu/drm/panel/panel-himax-hx8279.c
>> +++ b/drivers/gpu/drm/panel/panel-himax-hx8279.c
>> @@ -815,7 +815,7 @@ static int hx8279_check_gmux_config(struct hx8279 *hx, struct device *dev)
>>   static int hx8279_check_goa_config(struct hx8279 *hx, struct device *dev)
>>   {
>>       const struct hx8279_panel_desc *desc = hx->desc;
>> -    bool goa_odd_valid, goa_even_valid;
>> +    bool goa_odd_valid = true, goa_even_valid = true;
>>       int i, num_zero, num_clr = 0;
>>       /* Up to 4 zero values is a valid configuration. Check them all. */
>>
>> ---
>> base-commit: dcbd5dcc956e2331414fd7020b4655df08deeb87
>> change-id: 20250422-panel-himax-hx8279-fix-sometimes-uninitialized-207354fb930c
>>
>> Best regards,
> 
> Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>

I'll wait a few days until AngeloGioacchino Del Regno reviews it to be sure
it's the right fix.

Thanks,
Neil