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[60.250.196.139]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-369c4bb4d4dsm4170018a91.1.2026.05.19.19.14.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 19 May 2026 19:14:44 -0700 (PDT) Message-ID: <2a49734a-c4e7-4818-a024-6c944af93020@gmail.com> Date: Wed, 20 May 2026 10:14:38 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/3] clk: nuvoton: ma35d1: fix PLL_CTL1_FRAC bit field width and fractional calc To: Brian Masney 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 References: <20260513055626.1070533-1-a0987203069@gmail.com> <20260513055626.1070533-3-a0987203069@gmail.com> Content-Language: en-US From: Joey Lu In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 5/19/2026 10:53 PM, Brian Masney wrote: > 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 Thanks for the suggestion! I'll update this to use DIV_ROUND_CLOSEST_ULL in the next version. BR, Joey > >> + pll_freq = div_u64((u64)parent_rate * n, 1000 * m * p); >> } >> return pll_freq; >> } >> -- >> 2.43.0 >>