[PATCH] drm/i915/display: Fix u32 overflow in SNPS PHY HDMI PLL setup

[Nautiyal, Ankit K]

On 5/28/2025 12:15 PM, Dibin Moolakadan Subrahmanian wrote:
> When configuring the HDMI PLL, calculations use DIV_ROUND_UP_ULL and
> DIV_ROUND_DOWN_ULL macros, which internally rely on do_div. However, do_div
> expects a 32-bit (u32) divisor, and at higher data rates, the divisor can
> exceed this limit. This leads to incorrect division results and
> ultimately misconfigured PLL values.
> This fix replaces do_div calls with  div64_base64 calls where diviser
> can exceed u32 limit.
>
> Signed-off-by: Dibin Moolakadan Subrahmanian <dibin.moolakadan.subrahmanian at intel.com>
> Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
> Fixes: 5947642004bf ("drm/i915/display: Add support for SNPS PHY HDMI PLL algorithm for DG2")

Need to have fixes tag in the beginning of the trailer. Can be fixed 
while merging though.


Regards,

Ankit


> Cc: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
> Cc: Suraj Kandpal <suraj.kandpal at intel.com>
> Cc: Jani Nikula <jani.nikula at intel.com>
> ---
>   .../gpu/drm/i915/display/intel_snps_hdmi_pll.c   | 16 ++++++++--------
>   1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_snps_hdmi_pll.c b/drivers/gpu/drm/i915/display/intel_snps_hdmi_pll.c
> index c6321dafef4f..74bb3bedf30f 100644
> --- a/drivers/gpu/drm/i915/display/intel_snps_hdmi_pll.c
> +++ b/drivers/gpu/drm/i915/display/intel_snps_hdmi_pll.c
> @@ -41,12 +41,12 @@ static s64 interp(s64 x, s64 x1, s64 x2, s64 y1, s64 y2)
>   {
>   	s64 dydx;
>   
> -	dydx = DIV_ROUND_UP_ULL((y2 - y1) * 100000, (x2 - x1));
> +	dydx = DIV64_U64_ROUND_UP((y2 - y1) * 100000, (x2 - x1));
>   
> -	return (y1 + DIV_ROUND_UP_ULL(dydx * (x - x1), 100000));
> +	return (y1 + DIV64_U64_ROUND_UP(dydx * (x - x1), 100000));
>   }
>   
> -static void get_ana_cp_int_prop(u32 vco_clk,
> +static void get_ana_cp_int_prop(u64 vco_clk,
>   				u32 refclk_postscalar,
>   				int mpll_ana_v2i,
>   				int c, int a,
> @@ -115,16 +115,16 @@ static void get_ana_cp_int_prop(u32 vco_clk,
>   								      CURVE0_MULTIPLIER));
>   
>   	scaled_interpolated_sqrt =
> -			int_sqrt(DIV_ROUND_UP_ULL(interpolated_product, vco_div_refclk_float) *
> +			int_sqrt(DIV64_U64_ROUND_UP(interpolated_product, vco_div_refclk_float) *
>   			DIV_ROUND_DOWN_ULL(1000000000000ULL, 55));
>   
>   	/* Scale vco_div_refclk for ana_cp_int */
>   	scaled_vco_div_refclk2 = DIV_ROUND_UP_ULL(vco_div_refclk_float, 1000000);
> -	adjusted_vco_clk2 = 1460281 * DIV_ROUND_UP_ULL(scaled_interpolated_sqrt *
> +	adjusted_vco_clk2 = 1460281 * DIV64_U64_ROUND_UP(scaled_interpolated_sqrt *
>   						       scaled_vco_div_refclk2,
>   						       curve_1_interpolated);
>   
> -	*ana_cp_prop = DIV_ROUND_UP_ULL(adjusted_vco_clk2, curve_2_scaled2);
> +	*ana_cp_prop = DIV64_U64_ROUND_UP(adjusted_vco_clk2, curve_2_scaled2);
>   	*ana_cp_prop = max(1, min(*ana_cp_prop, 127));
>   }
>   
> @@ -165,10 +165,10 @@ static void compute_hdmi_tmds_pll(u64 pixel_clock, u32 refclk,
>   	/* Select appropriate v2i point */
>   	if (datarate <= INTEL_SNPS_PHY_HDMI_9999MHZ) {
>   		mpll_ana_v2i = 2;
> -		tx_clk_div = ilog2(DIV_ROUND_DOWN_ULL(INTEL_SNPS_PHY_HDMI_9999MHZ, datarate));
> +		tx_clk_div = ilog2(div64_u64(INTEL_SNPS_PHY_HDMI_9999MHZ, datarate));
>   	} else {
>   		mpll_ana_v2i = 3;
> -		tx_clk_div = ilog2(DIV_ROUND_DOWN_ULL(INTEL_SNPS_PHY_HDMI_16GHZ, datarate));
> +		tx_clk_div = ilog2(div64_u64(INTEL_SNPS_PHY_HDMI_16GHZ, datarate));
>   	}
>   	vco_clk = (datarate << tx_clk_div) >> 1;
>