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

[Jani Nikula]

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?


>  
>  	if (!p) {

-- 
Jani Nikula, Intel