From 52aef653c3d0c24013dfa9eccf692594eacdbe17 Mon Sep 17 00:00:00 2001 From: Alexey Charkov Date: Thu, 23 Jul 2026 14:21:58 +0400 Subject: [PATCH] clk: rockchip: Fix the fractional part denominator on RK3588/RK3576 PLLs According to the TRM, the fractional PLL coefficient should be divided by 65536 rather than 65535 to obtain the output rate. Fix the denominator and add a comment with the TRM provided clock formulae for future reference. See RK3576 TRM Part 1 V1.2 section 2.13.1.4 Setting Guide on P, M, S and K or equivalently RK3588 TRM part 1 V1.0 section 2.17.1.4 Setting Guide on P, M, S and K. Fractional PLL rates don't seem to be used by any current mainline consumers, so this is purely a correctness fix. It will also be important to properly support DisplayPort output going forward, as the video output controller derives its pixel clock from system PLLs with no dedicated PHY PLL option for DP unlike HDMI, and some display modes are only achievable with fractional PLL rates. Fixes: 8f6594494b1c ("clk: rockchip: add pll type for RK3588") Signed-off-by: Alexey Charkov Reviewed-by: Quentin Schulz Link: https://patch.msgid.link/20260723-rk3588-fracpll-v2-1-3adfb9dda235@flipper.net Signed-off-by: Heiko Stuebner --- drivers/clk/rockchip/clk-pll.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/drivers/clk/rockchip/clk-pll.c b/drivers/clk/rockchip/clk-pll.c index 6b853800cb6b..bf8acf7cee0d 100644 --- a/drivers/clk/rockchip/clk-pll.c +++ b/drivers/clk/rockchip/clk-pll.c @@ -900,6 +900,13 @@ static void rockchip_rk3588_pll_get_params(struct rockchip_clk_pll *pll, rate->k = ((pllcon >> RK3588_PLLCON2_K_SHIFT) & RK3588_PLLCON2_K_MASK); } +/* + * 2250 MHz <= Fvco <= 4500 MHz + * For Fvco > 3 GHz: period jitter +-1% frac PLL, +-0.75% int PLL + * For Fvco < 3 GHz: period jitter +-2% frac PLL, +-1.50% int PLL + * Fvco = ((m + k / 65536) * Fin) / p + * Fout = ((m + k / 65536) * Fin) / (p * 2^s) + */ static unsigned long rockchip_rk3588_pll_recalc_rate(struct clk_hw *hw, unsigned long prate) { struct rockchip_clk_pll *pll = to_rockchip_clk_pll(hw); @@ -915,7 +922,7 @@ static unsigned long rockchip_rk3588_pll_recalc_rate(struct clk_hw *hw, unsigned /* fractional mode */ u64 frac_rate64 = prate * cur.k; - postdiv = cur.p * 65535; + postdiv = cur.p * 65536; do_div(frac_rate64, postdiv); rate64 += frac_rate64; }