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2024-10-09 244b2c5ca8b14627e4a17755e5922221e121c771 
 kernel/drivers/pwm/pwm-tegra.c
....@@ -1,24 +1,39 @@
1
+// SPDX-License-Identifier: GPL-2.0-or-later
12 /*
23  * drivers/pwm/pwm-tegra.c
34  *
45  * Tegra pulse-width-modulation controller driver
56  *
6
- * Copyright (c) 2010, NVIDIA Corporation.
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+ * Copyright (c) 2010-2020, NVIDIA Corporation.
78  * Based on arch/arm/plat-mxc/pwm.c by Sascha Hauer <s.hauer@pengutronix.de>
89  *
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- * This program is free software; you can redistribute it and/or modify
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- * it under the terms of the GNU General Public License as published by
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- * the Free Software Foundation; either version 2 of the License, or
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- * (at your option) any later version.
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+ * Overview of Tegra Pulse Width Modulator Register:
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+ * 1. 13-bit: Frequency division (SCALE)
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+ * 2. 8-bit : Pulse division (DUTY)
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+ * 3. 1-bit : Enable bit
1314  *
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- * This program is distributed in the hope that it will be useful, but WITHOUT
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- * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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- * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
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- * more details.
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+ * The PWM clock frequency is divided by 256 before subdividing it based
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+ * on the programmable frequency division value to generate the required
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+ * frequency for PWM output. The maximum output frequency that can be
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+ * achieved is (max rate of source clock) / 256.
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+ * e.g. if source clock rate is 408 MHz, maximum output frequency can be:
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+ * 408 MHz/256 = 1.6 MHz.
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+ * This 1.6 MHz frequency can further be divided using SCALE value in PWM.
1822  *
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- * You should have received a copy of the GNU General Public License along
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- * with this program; if not, write to the Free Software Foundation, Inc.,
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- * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
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+ * PWM pulse width: 8 bits are usable [23:16] for varying pulse width.
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+ * To achieve 100% duty cycle, program Bit [24] of this register to
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+ * 1’b1. In which case the other bits [23:16] are set to don't care.
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+ *
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+ * Limitations:
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+ * -	When PWM is disabled, the output is driven to inactive.
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+ * -	It does not allow the current PWM period to complete and
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+ *	stops abruptly.
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+ *
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+ * -	If the register is reconfigured while PWM is running,
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+ *	it does not complete the currently running period.
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+ *
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+ * -	If the user input duty is beyond acceptible limits,
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+ *	-EINVAL is returned.
2237  */
2338 
2439 #include <linux/clk.h>
....@@ -54,6 +69,7 @@
5469 	struct reset_control*rst;
5570 
5671 	unsigned long clk_rate;
72
+	unsigned long min_period_ns;
5773 
5874 	void __iomem *regs;
5975 
....@@ -81,7 +97,7 @@
8197 {
8298 	struct tegra_pwm_chip *pc = to_tegra_pwm_chip(chip);
8399 	unsigned long long c = duty_ns, hz;
84
-	unsigned long rate;
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+	unsigned long rate, required_clk_rate;
85101 	u32 val = 0;
86102 	int err;
87103 
....@@ -96,9 +112,47 @@
96112 	val = (u32)c << PWM_DUTY_SHIFT;
97113 
98114 	/*
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+	 *  min period = max clock limit >> PWM_DUTY_WIDTH
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+	 */
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+	if (period_ns < pc->min_period_ns)
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+		return -EINVAL;
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+
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+	/*
99121 	 * Compute the prescaler value for which (1 << PWM_DUTY_WIDTH)
100122 	 * cycles at the PWM clock rate will take period_ns nanoseconds.
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+	 *
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+	 * num_channels: If single instance of PWM controller has multiple
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+	 * channels (e.g. Tegra210 or older) then it is not possible to
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+	 * configure separate clock rates to each of the channels, in such
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+	 * case the value stored during probe will be referred.
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+	 *
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+	 * If every PWM controller instance has one channel respectively, i.e.
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+	 * nums_channels == 1 then only the clock rate can be modified
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+	 * dynamically (e.g. Tegra186 or Tegra194).
101132 	 */
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+	if (pc->soc->num_channels == 1) {
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+		/*
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+		 * Rate is multiplied with 2^PWM_DUTY_WIDTH so that it matches
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+		 * with the maximum possible rate that the controller can
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+		 * provide. Any further lower value can be derived by setting
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+		 * PFM bits[0:12].
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+		 *
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+		 * required_clk_rate is a reference rate for source clock and
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+		 * it is derived based on user requested period. By setting the
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+		 * source clock rate as required_clk_rate, PWM controller will
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+		 * be able to configure the requested period.
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+		 */
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+		required_clk_rate = DIV_ROUND_UP_ULL((u64)NSEC_PER_SEC << PWM_DUTY_WIDTH,
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+						     period_ns);
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+
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+		err = clk_set_rate(pc->clk, required_clk_rate);
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+		if (err < 0)
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+			return -EINVAL;
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+
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+		/* Store the new rate for further references */
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+		pc->clk_rate = clk_get_rate(pc->clk);
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+	}
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+
102156 	rate = pc->clk_rate >> PWM_DUTY_WIDTH;
103157 
104158 	/* Consider precision in PWM_SCALE_WIDTH rate calculation */
....@@ -107,7 +161,7 @@
107161 
108162 	/*
109163 	 * Since the actual PWM divider is the register's frequency divider
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-	 * field minus 1, we need to decrement to get the correct value to
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+	 * field plus 1, we need to decrement to get the correct value to
111165 	 * write to the register.
112166 	 */
113167 	if (rate > 0)
....@@ -218,6 +272,10 @@
218272 	 */
219273 	pwm->clk_rate = clk_get_rate(pwm->clk);
220274 
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+	/* Set minimum limit of PWM period for the IP */
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+	pwm->min_period_ns =
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+	    (NSEC_PER_SEC / (pwm->soc->max_frequency >> PWM_DUTY_WIDTH)) + 1;
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+
221279 	pwm->rst = devm_reset_control_get_exclusive(&pdev->dev, "pwm");
222280 	if (IS_ERR(pwm->rst)) {
223281 		ret = PTR_ERR(pwm->rst);
....@@ -282,12 +340,17 @@
282340 	.max_frequency = 102000000UL,
283341 };
284342 
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+static const struct tegra_pwm_soc tegra194_pwm_soc = {
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+	.num_channels = 1,
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+	.max_frequency = 408000000UL,
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+};
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+
285348 static const struct of_device_id tegra_pwm_of_match[] = {
286349 	{ .compatible = "nvidia,tegra20-pwm", .data = &tegra20_pwm_soc },
287350 	{ .compatible = "nvidia,tegra186-pwm", .data = &tegra186_pwm_soc },
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+	{ .compatible = "nvidia,tegra194-pwm", .data = &tegra194_pwm_soc },
288352 	{ }
289353 };
290
-
291354 MODULE_DEVICE_TABLE(of, tegra_pwm_of_match);
292355 
293356 static const struct dev_pm_ops tegra_pwm_pm_ops = {
....@@ -307,5 +370,6 @@
307370 module_platform_driver(tegra_pwm_driver);
308371 
309372 MODULE_LICENSE("GPL");
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-MODULE_AUTHOR("NVIDIA Corporation");
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+MODULE_AUTHOR("Sandipan Patra <spatra@nvidia.com>");
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+MODULE_DESCRIPTION("Tegra PWM controller driver");
311375 MODULE_ALIAS("platform:tegra-pwm");