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[73.183.52.120]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-5164568a275sm165644671cf.5.2026.05.19.07.53.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 19 May 2026 07:53:54 -0700 (PDT) Date: Tue, 19 May 2026 10:53:53 -0400 From: Brian Masney To: Joey Lu Cc: mturquette@baylibre.com, sboyd@kernel.org, ychuang3@nuvoton.com, schung@nuvoton.com, yclu4@nuvoton.com, linux-arm-kernel@lists.infradead.org, linux-clk@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 2/3] clk: nuvoton: ma35d1: fix PLL_CTL1_FRAC bit field width and fractional calc Message-ID: References: <20260513055626.1070533-1-a0987203069@gmail.com> <20260513055626.1070533-3-a0987203069@gmail.com> Precedence: bulk X-Mailing-List: linux-clk@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260513055626.1070533-3-a0987203069@gmail.com> User-Agent: Mutt/2.3.1 (2026-03-20) Hi Joey, On Wed, May 13, 2026 at 01:56:25PM +0800, Joey Lu wrote: > PLL_CTL1_FRAC was defined as GENMASK(31, 24), covering only 8 bits. > The hardware fractional field occupies bits [31:8] (24 bits), so the > mask must be GENMASK(31, 8). > > The previous fractional-mode calculation used FIELD_MAX(PLL_CTL1_FRAC) > as the denominator to obtain 2 decimal places. With the corrected 24-bit > mask the old divisor is wrong; replace the arithmetic with a proper > 24-bit fixed-point rounding to 3 decimal places: > > n_frac = n * 1000 + (x * 1000 + 500) >> 24 > > The +500 term provides round-to-nearest before the right shift. > > Fixes: 691521a367cf ("clk: nuvoton: Add clock driver for ma35d1 clock controller") > Signed-off-by: Joey Lu > --- > drivers/clk/nuvoton/clk-ma35d1-pll.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/drivers/clk/nuvoton/clk-ma35d1-pll.c b/drivers/clk/nuvoton/clk-ma35d1-pll.c > index bfedd45bd04b..7e6b30d20c01 100644 > --- a/drivers/clk/nuvoton/clk-ma35d1-pll.c > +++ b/drivers/clk/nuvoton/clk-ma35d1-pll.c > @@ -48,7 +48,7 @@ > #define PLL_CTL1_PD BIT(0) > #define PLL_CTL1_BP BIT(1) > #define PLL_CTL1_OUTDIV GENMASK(6, 4) > -#define PLL_CTL1_FRAC GENMASK(31, 24) > +#define PLL_CTL1_FRAC GENMASK(31, 8) > #define PLL_CTL2_SLOPE GENMASK(23, 0) > > #define INDIV_MIN 1 > @@ -113,9 +113,9 @@ static unsigned long ma35d1_calc_pll_freq(u8 mode, u32 *reg_ctl, unsigned long p > pll_freq = div_u64(pll_freq, m * p); > } else { > x = FIELD_GET(PLL_CTL1_FRAC, reg_ctl[1]); > - /* 2 decimal places floating to integer (ex. 1.23 to 123) */ > - n = n * 100 + ((x * 100) / FIELD_MAX(PLL_CTL1_FRAC)); > - pll_freq = div_u64(parent_rate * n, 100 * m * p); > + /* x is 24-bit fractional part, convert to 3 decimal digits */ > + n = n * 1000 + (u32)(((u64)x * 1000 + 500) >> 24); ^^^^^^^^^^^^^^^^^^^^^ You should be able to use DIV_ROUND_CLOSEST_ULL() here. Brian > + pll_freq = div_u64((u64)parent_rate * n, 1000 * m * p); > } > return pll_freq; > } > -- > 2.43.0 >