[PATCH] drm/i915/dsi: Fix overflow issue in pclk parsing

[Jani Nikula]

On Wed, 06 Aug 2025, Jani Nikula <jani.nikula at linux.intel.com> wrote:
> On Wed, 06 Aug 2025, Jouni Högander <jouni.hogander at intel.com> wrote:
>> Parsed divider p will overflow and is considered being valid divider in
>> case pll_ctl == 0.
>>
>> Fix this by using do while.
>>
>> Signed-off-by: Jouni Högander <jouni.hogander at intel.com>
>> ---
>>  drivers/gpu/drm/i915/display/vlv_dsi_pll.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/display/vlv_dsi_pll.c b/drivers/gpu/drm/i915/display/vlv_dsi_pll.c
>> index b52463fdec47..f56985c3da54 100644
>> --- a/drivers/gpu/drm/i915/display/vlv_dsi_pll.c
>> +++ b/drivers/gpu/drm/i915/display/vlv_dsi_pll.c
>> @@ -142,10 +142,10 @@ static int vlv_dsi_pclk(struct intel_encoder *encoder,
>>  	pll_div &= DSI_PLL_M1_DIV_MASK;
>>  	pll_div = pll_div >> DSI_PLL_M1_DIV_SHIFT;
>>  
>> -	while (pll_ctl) {
>> +	do {
>>  		pll_ctl = pll_ctl >> 1;
>>  		p++;
>> -	}
>> +	} while (pll_ctl);
>>  	p--;
>
> Alternatively, use p = lfs(pll_ctl), check the return value, and p--
> after that?

Should be fls(). (Find last set.)

>
>
>>  
>>  	if (!p) {

-- 
Jani Nikula, Intel