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Sun, 19 Jul 2026 14:13:44 -0700 (PDT) From: =?UTF-8?q?Juan=20Manuel=20L=C3=B3pez=20Carrillo?= To: Michael Turquette , Stephen Boyd , Chen-Yu Tsai , Jernej Skrabec , Samuel Holland Cc: Brian Masney , Andre Przywara , Rob Herring , Krzysztof Kozlowski , Conor Dooley , linux-clk@vger.kernel.org, linux-sunxi@lists.linux.dev, linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, =?UTF-8?q?Juan=20Manuel=20L=C3=B3pez=20Carrillo?= Subject: [PATCH v1 1/4] clk: sunxi-ng: add cycle-masking divider (maskdiv) clock type Date: Sun, 19 Jul 2026 23:13:16 +0200 Message-ID: <20260719211319.982285-2-juanmanuellopezcarrillo@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260719211319.982285-1-juanmanuellopezcarrillo@gmail.com> References: <20260719211319.982285-1-juanmanuellopezcarrillo@gmail.com> Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Some mod clocks do not divide their parent with a linear M+1 divider: the M factor masks (swallows) M pulses out of every 2^width parent cycles, so the average output rate is rate = parent * (2^width - M) / 2^width and the surviving pulses keep the parent period. The A523/T527 GPU clock (GPU_CLK_REG, 0x670) is such a divider: "FACTOR_M: mask M cycles at 16 cycles", GPU_CLK = Clock Source * ((16-M)/16) (T527 user manual v0.92, section 2.7.6.58). Modelling these registers with the linear ccu_div type programs a faster clock than requested for every M > 0 (e.g. M=1 on a 800 MHz parent yields 750 MHz, not 400 MHz). Add a small ccu type implementing the masking semantics. Because the masked output is not an even pulse train, determine_rate prefers, among the parents that reach the requested rate, the one needing the least masking. set_rate_and_parent follows the same ordering rule as clk_composite_set_rate_and_parent() so no intermediate configuration overshoots both the old and the new rate. Signed-off-by: Juan Manuel López Carrillo --- drivers/clk/sunxi-ng/Makefile | 1 + drivers/clk/sunxi-ng/ccu_maskdiv.c | 199 +++++++++++++++++++++++++++++ drivers/clk/sunxi-ng/ccu_maskdiv.h | 71 ++++++++++ 3 files changed, 271 insertions(+) create mode 100644 drivers/clk/sunxi-ng/ccu_maskdiv.c create mode 100644 drivers/clk/sunxi-ng/ccu_maskdiv.h diff --git a/drivers/clk/sunxi-ng/Makefile b/drivers/clk/sunxi-ng/Makefile index a1c4087d7..26313083c 100644 --- a/drivers/clk/sunxi-ng/Makefile +++ b/drivers/clk/sunxi-ng/Makefile @@ -10,6 +10,7 @@ sunxi-ccu-y += ccu_reset.o # Base clock types sunxi-ccu-y += ccu_div.o sunxi-ccu-y += ccu_frac.o +sunxi-ccu-y += ccu_maskdiv.o sunxi-ccu-y += ccu_gate.o sunxi-ccu-y += ccu_mux.o sunxi-ccu-y += ccu_mult.o diff --git a/drivers/clk/sunxi-ng/ccu_maskdiv.c b/drivers/clk/sunxi-ng/ccu_maskdiv.c new file mode 100644 index 000000000..2d3cccf08 --- /dev/null +++ b/drivers/clk/sunxi-ng/ccu_maskdiv.c @@ -0,0 +1,199 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Copyright (c) 2026 Juan Manuel López Carrillo + * + * Cycle-masking divider: the M factor masks M pulses out of every + * 2^width parent cycles instead of dividing the parent rate, so + * + * rate = parent * (2^width - M) / 2^width + * + * The masked output is not an even pulse train: the surviving pulses + * keep the parent period. Rate selection therefore prefers, among the + * parents that reach the requested rate, the one needing the least + * masking. + */ + +#include +#include +#include + +#include "ccu_gate.h" +#include "ccu_maskdiv.h" + +static unsigned long ccu_maskdiv_calc_rate(unsigned long parent_rate, + unsigned int m, unsigned int width) +{ + unsigned int n = 1 << width; + + return div_u64((u64)parent_rate * (n - m), n); +} + +/* + * Smallest M (least masking) whose output does not exceed the requested + * rate; masking everything (M == 2^width) is never returned. + */ +static unsigned int ccu_maskdiv_find_m(unsigned long parent_rate, + unsigned long rate, unsigned int width) +{ + unsigned int n = 1 << width; + u64 kept; + + if (!parent_rate || rate >= parent_rate) + return 0; + + kept = div64_ul((u64)rate * n, parent_rate); + if (!kept) + kept = 1; + + return n - (unsigned int)kept; +} + +static void ccu_maskdiv_disable(struct clk_hw *hw) +{ + struct ccu_maskdiv *cmd = hw_to_ccu_maskdiv(hw); + + return ccu_gate_helper_disable(&cmd->common, cmd->enable); +} + +static int ccu_maskdiv_enable(struct clk_hw *hw) +{ + struct ccu_maskdiv *cmd = hw_to_ccu_maskdiv(hw); + + return ccu_gate_helper_enable(&cmd->common, cmd->enable); +} + +static int ccu_maskdiv_is_enabled(struct clk_hw *hw) +{ + struct ccu_maskdiv *cmd = hw_to_ccu_maskdiv(hw); + + return ccu_gate_helper_is_enabled(&cmd->common, cmd->enable); +} + +static unsigned long ccu_maskdiv_recalc_rate(struct clk_hw *hw, + unsigned long parent_rate) +{ + struct ccu_maskdiv *cmd = hw_to_ccu_maskdiv(hw); + unsigned int m; + u32 reg; + + reg = readl(cmd->common.base + cmd->common.reg); + m = (reg >> cmd->shift) & ((1 << cmd->width) - 1); + + return ccu_maskdiv_calc_rate(parent_rate, m, cmd->width); +} + +static int ccu_maskdiv_determine_rate(struct clk_hw *hw, + struct clk_rate_request *req) +{ + struct ccu_maskdiv *cmd = hw_to_ccu_maskdiv(hw); + unsigned long best_rate = 0, best_parent_rate = 0; + struct clk_hw *best_parent = NULL; + unsigned int best_m = UINT_MAX; + unsigned int i; + + for (i = 0; i < clk_hw_get_num_parents(hw); i++) { + struct clk_hw *parent = clk_hw_get_parent_by_index(hw, i); + unsigned long parent_rate, new_rate; + unsigned int m; + + if (!parent) + continue; + + parent_rate = clk_hw_get_rate(parent); + m = ccu_maskdiv_find_m(parent_rate, req->rate, cmd->width); + new_rate = ccu_maskdiv_calc_rate(parent_rate, m, cmd->width); + + if (new_rate > req->rate) + continue; + + /* Closest rate first; on ties, the least masking */ + if (new_rate > best_rate || + (new_rate == best_rate && m < best_m)) { + best_rate = new_rate; + best_parent_rate = parent_rate; + best_parent = parent; + best_m = m; + } + } + + if (!best_parent) + return -EINVAL; + + req->best_parent_hw = best_parent; + req->best_parent_rate = best_parent_rate; + req->rate = best_rate; + + return 0; +} + +static int ccu_maskdiv_set_rate(struct clk_hw *hw, unsigned long rate, + unsigned long parent_rate) +{ + struct ccu_maskdiv *cmd = hw_to_ccu_maskdiv(hw); + unsigned int m; + unsigned long flags; + u32 reg; + + m = ccu_maskdiv_find_m(parent_rate, rate, cmd->width); + + spin_lock_irqsave(cmd->common.lock, flags); + + reg = readl(cmd->common.base + cmd->common.reg); + reg &= ~GENMASK(cmd->shift + cmd->width - 1, cmd->shift); + writel(reg | (m << cmd->shift), cmd->common.base + cmd->common.reg); + + spin_unlock_irqrestore(cmd->common.lock, flags); + + return 0; +} + +static u8 ccu_maskdiv_get_parent(struct clk_hw *hw) +{ + struct ccu_maskdiv *cmd = hw_to_ccu_maskdiv(hw); + + return ccu_mux_helper_get_parent(&cmd->common, &cmd->mux); +} + +static int ccu_maskdiv_set_parent(struct clk_hw *hw, u8 index) +{ + struct ccu_maskdiv *cmd = hw_to_ccu_maskdiv(hw); + + return ccu_mux_helper_set_parent(&cmd->common, &cmd->mux, index); +} + +static int ccu_maskdiv_set_rate_and_parent(struct clk_hw *hw, + unsigned long rate, + unsigned long parent_rate, u8 index) +{ + /* + * Same ordering rule as clk_composite_set_rate_and_parent(): if + * switching the mux with the current M would overshoot the + * requested rate, program the divider first, so the + * intermediate rate never exceeds both the old and the new + * rate. + */ + if (ccu_maskdiv_recalc_rate(hw, parent_rate) > rate) { + ccu_maskdiv_set_rate(hw, rate, parent_rate); + ccu_maskdiv_set_parent(hw, index); + } else { + ccu_maskdiv_set_parent(hw, index); + ccu_maskdiv_set_rate(hw, rate, parent_rate); + } + + return 0; +} + +const struct clk_ops ccu_maskdiv_ops = { + .disable = ccu_maskdiv_disable, + .enable = ccu_maskdiv_enable, + .is_enabled = ccu_maskdiv_is_enabled, + + .get_parent = ccu_maskdiv_get_parent, + .set_parent = ccu_maskdiv_set_parent, + + .determine_rate = ccu_maskdiv_determine_rate, + .recalc_rate = ccu_maskdiv_recalc_rate, + .set_rate = ccu_maskdiv_set_rate, + .set_rate_and_parent = ccu_maskdiv_set_rate_and_parent, +}; +EXPORT_SYMBOL_NS_GPL(ccu_maskdiv_ops, "SUNXI_CCU"); diff --git a/drivers/clk/sunxi-ng/ccu_maskdiv.h b/drivers/clk/sunxi-ng/ccu_maskdiv.h new file mode 100644 index 000000000..3cbfce064 --- /dev/null +++ b/drivers/clk/sunxi-ng/ccu_maskdiv.h @@ -0,0 +1,71 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Copyright (c) 2026 Juan Manuel López Carrillo + */ + +#ifndef _CCU_MASKDIV_H_ +#define _CCU_MASKDIV_H_ + +#include + +#include "ccu_common.h" +#include "ccu_mux.h" + +/* + * struct ccu_maskdiv - cycle-masking ("fractional") divider + * + * This divider does not divide the parent clock: it masks (swallows) M + * pulses out of every 2^width parent cycles, so the average output rate + * is + * + * rate = parent * (2^width - M) / 2^width + * + * with the remaining pulses keeping the parent period. The A523/T527 + * GPU clock (GPU_CLK_REG, 0x670) is such a divider: "FACTOR_M: mask M + * cycles at 16 cycles", GPU_CLK = Clock Source * ((16-M)/16) (T527 user + * manual v0.92, section 2.7.6.58). + * + * @shift: shift of the M field in the register + * @width: width of the M field; the mask window is 2^width cycles + */ +struct ccu_maskdiv { + u32 enable; + + u8 shift; + u8 width; + + struct ccu_mux_internal mux; + struct ccu_common common; +}; + +#define SUNXI_CCU_MASKDIV_HW_WITH_MUX_TABLE_GATE(_struct, _name, \ + _parents, _table, \ + _reg, \ + _mshift, _mwidth, \ + _muxshift, _muxwidth, \ + _gate, _flags) \ + struct ccu_maskdiv _struct = { \ + .enable = _gate, \ + .shift = _mshift, \ + .width = _mwidth, \ + .mux = _SUNXI_CCU_MUX_TABLE(_muxshift, _muxwidth, \ + _table), \ + .common = { \ + .reg = _reg, \ + .hw.init = CLK_HW_INIT_PARENTS_HW(_name, \ + _parents, \ + &ccu_maskdiv_ops, \ + _flags), \ + }, \ + } + +static inline struct ccu_maskdiv *hw_to_ccu_maskdiv(struct clk_hw *hw) +{ + struct ccu_common *common = hw_to_ccu_common(hw); + + return container_of(common, struct ccu_maskdiv, common); +} + +extern const struct clk_ops ccu_maskdiv_ops; + +#endif /* _CCU_MASKDIV_H_ */ -- 2.47.3