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Thu, 14 May 2026 08:11:03 -0700 (PDT) From: Jerome Brunet To: Jian Hu via B4 Relay Cc: Michael Turquette , Stephen Boyd , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Neil Armstrong , Xianwei Zhao , Kevin Hilman , Martin Blumenstingl , jian.hu@amlogic.com, linux-kernel@vger.kernel.org, linux-clk@vger.kernel.org, devicetree@vger.kernel.org, linux-amlogic@lists.infradead.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH 07/10] clk: amlogic: Support POWER_OF_TWO for PLL pre-divider In-Reply-To: <20260511-b4-a9_clk-v1-7-41cb4071b7c9@amlogic.com> (Jian Hu via's message of "Mon, 11 May 2026 20:47:29 +0800") References: <20260511-b4-a9_clk-v1-0-41cb4071b7c9@amlogic.com> <20260511-b4-a9_clk-v1-7-41cb4071b7c9@amlogic.com> User-Agent: mu4e 1.12.9; emacs 30.1 Date: Thu, 14 May 2026 17:11:01 +0200 Message-ID: <1jy0hm6n7e.fsf@starbuckisacylon.baylibre.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On lun. 11 mai 2026 at 20:47, Jian Hu via B4 Relay wrote: > From: Jian Hu > > The A9 PLL pre-divider uses a division factor of 2^n to ensure a clock > duty cycle of 50% after predivision. > > Add flag 'CLK_MESON_PLL_N_POWER_OF_TWO' to indicate that the PLL > pre-divider division factor is 2^n. I understand what you are doing here but I have to ask why this can't be implemented with independent dividers that already supports power of 2 ? > > Signed-off-by: Jian Hu > --- > drivers/clk/meson/clk-pll.c | 28 +++++++++++++++++++++++----- > drivers/clk/meson/clk-pll.h | 2 ++ > 2 files changed, 25 insertions(+), 5 deletions(-) > > diff --git a/drivers/clk/meson/clk-pll.c b/drivers/clk/meson/clk-pll.c > index 8568ad6ba7b6..49483e431d44 100644 > --- a/drivers/clk/meson/clk-pll.c > +++ b/drivers/clk/meson/clk-pll.c > @@ -66,6 +66,9 @@ static unsigned long __pll_params_to_rate(unsigned long parent_rate, > rate += DIV_ROUND_UP_ULL(frac_rate, frac_max); > } > > + if (pll->flags & CLK_MESON_PLL_N_POWER_OF_TWO) > + n = 1 << n; > + > return DIV_ROUND_UP_ULL(rate, n); > } > > @@ -83,7 +86,7 @@ static unsigned long meson_clk_pll_recalc_rate(struct clk_hw *hw, > * it would result in a division by zero. The rate can't be > * calculated in this case > */ > - if (n == 0) > + if (n == 0 && !(pll->flags & CLK_MESON_PLL_N_POWER_OF_TWO)) > return 0; > > m = meson_parm_read(clk->map, &pll->m); > @@ -103,7 +106,12 @@ static unsigned int __pll_params_with_frac(unsigned long rate, > { > unsigned int frac_max = pll->frac_max ? pll->frac_max : > (1 << pll->frac.width); > - u64 val = (u64)rate * n; > + u64 val; > + > + if (pll->flags & CLK_MESON_PLL_N_POWER_OF_TWO) > + n = 1 << n; > + > + val = (u64)rate * n; > > /* Bail out if we are already over the requested rate */ > if (rate < parent_rate * m / n) > @@ -142,7 +150,8 @@ static int meson_clk_get_pll_table_index(unsigned int index, > unsigned int *n, > struct meson_clk_pll_data *pll) > { > - if (!pll->table[index].n) > + if (!pll->table[index].n && > + !(pll->flags & CLK_MESON_PLL_N_POWER_OF_TWO)) > return -EINVAL; > > *m = pll->table[index].m; > @@ -156,7 +165,12 @@ static unsigned int meson_clk_get_pll_range_m(unsigned long rate, > unsigned int n, > struct meson_clk_pll_data *pll) > { > - u64 val = (u64)rate * n; > + u64 val; > + > + if (pll->flags & CLK_MESON_PLL_N_POWER_OF_TWO) > + n = 1 << n; > + > + val = (u64)rate * n; > > if (__pll_round_closest_mult(pll)) > return DIV_ROUND_CLOSEST_ULL(val, parent_rate); > @@ -173,11 +187,15 @@ static int meson_clk_get_pll_range_index(unsigned long rate, > { > *n = index + 1; > > + if ((pll->flags & CLK_MESON_PLL_N_POWER_OF_TWO)) > + *n = index; > + > /* Check the predivider range */ > if (*n >= (1 << pll->n.width)) > return -EINVAL; > > - if (*n == 1) { > + if ((*n == 1 && !(pll->flags & CLK_MESON_PLL_N_POWER_OF_TWO)) || > + (*n == 0 && (pll->flags & CLK_MESON_PLL_N_POWER_OF_TWO))) { > /* Get the boundaries out the way */ > if (rate <= pll->range->min * parent_rate) { > *m = pll->range->min; > diff --git a/drivers/clk/meson/clk-pll.h b/drivers/clk/meson/clk-pll.h > index 1be7e6e77631..60b2772a54c8 100644 > --- a/drivers/clk/meson/clk-pll.h > +++ b/drivers/clk/meson/clk-pll.h > @@ -33,6 +33,8 @@ struct pll_mult_range { > #define CLK_MESON_PLL_L_DETECT_ACTIVE_HIGH BIT(2) > /* rst signal is active-low (Power-on reset) */ > #define CLK_MESON_PLL_RST_ACTIVE_LOW BIT(3) > +/* The division factor of the PLL pre-divider is 2^n */ > +#define CLK_MESON_PLL_N_POWER_OF_TWO BIT(4) > > struct meson_clk_pll_data { > struct parm en; -- Jerome