On Fri, 13 Jun 2025, Ankit Nautiyal ankit.k.nautiyal@intel.com wrote:
DIV_ROUND_CLOSEST_ULL uses do_div(), which expects a 32-bit divisor. When passing a 64-bit constant like CURVE2_MULTIPLIER, the value is silently truncated to u32, potentially leading to incorrect results on large divisors.
Replace DIV_ROUND_CLOSEST_ULL with div64_u64(), which correctly handles full 64-bit division. Since the result is clamped between 1 and 127, rounding is unnecessary and truncating division is sufficient.
I don't understand how you can make that conclusion. Please explain.
Would it be safer to just use DIV64_U64_ROUND_CLOSEST()?
Fixes: 5947642004bf ("drm/i915/display: Add support for SNPS PHY HDMI PLL algorithm for DG2") Cc: Ankit Nautiyal ankit.k.nautiyal@intel.com Cc: Suraj Kandpal suraj.kandpal@intel.com Cc: Jani Nikula jani.nikula@intel.com Cc: stable@vger.kernel.org # v6.15+ Signed-off-by: Ankit Nautiyal ankit.k.nautiyal@intel.com
drivers/gpu/drm/i915/display/intel_snps_hdmi_pll.c | 4 ++-- 1 file changed, 2 insertions(+), 2 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 74bb3bedf30f..ac609bdf6653 100644 --- a/drivers/gpu/drm/i915/display/intel_snps_hdmi_pll.c +++ b/drivers/gpu/drm/i915/display/intel_snps_hdmi_pll.c @@ -103,8 +103,8 @@ static void get_ana_cp_int_prop(u64 vco_clk, DIV_ROUND_DOWN_ULL(curve_1_interpolated, CURVE0_MULTIPLIER))); ana_cp_int_temp =
DIV_ROUND_CLOSEST_ULL(DIV_ROUND_DOWN_ULL(adjusted_vco_clk1, curve_2_scaled1),CURVE2_MULTIPLIER);
div64_u64(DIV_ROUND_DOWN_ULL(adjusted_vco_clk1, curve_2_scaled1),CURVE2_MULTIPLIER);*ana_cp_int = max(1, min(ana_cp_int_temp, 127));
Unrelated to this patch, but this should be:
*ana_cp_int = clamp(ana_cp_int_temp, 1, 127);
There's a similar issue with ana_cp_prop also in the file.
BR, Jani.