Some systems have clocks exposed to external devices. If the clock
controller supports duty-cycle configuration, such clocks can be used as
pwm outputs. In fact PWM and CLK subsystems are interfaced with in a
similar way and an "opposite" driver already exists (clk-pwm). Add a
driver that would enable pwm devices to be used via clk subsystem.
Signed-off-by: Nikita Travkin <nikita@xxxxxxx>
--
Changes in v2:
- Address Uwe's review comments:
- Round set clk rate up
- Add a description with limitations of the driver
- Disable and unprepare clock before removing pwmchip
Changes in v3:
- Use 64bit version of div round up
- Address Uwe's review comments:
- Reword the limitations to avoid incorrect claims
- Move the clk_enabled flag assignment
- Drop unnecessary statements
Changes in v5:
- add missed returns
Changes in v6:
- Unprepare the clock on error
- Drop redundant limitations points
Changes in v7:
- Rename some variables to be in line with common naming
Changes in v8:
- Document the glitch that happens inbetween multiple clock operations
---
drivers/pwm/Kconfig | 10 +++
drivers/pwm/Makefile | 1 +
drivers/pwm/pwm-clk.c | 148 ++++++++++++++++++++++++++++++++++++++++++
3 files changed, 159 insertions(+)
create mode 100644 drivers/pwm/pwm-clk.c
diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index 904de8d61828..60d13a949bc5 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -140,6 +140,16 @@ config PWM_BRCMSTB
To compile this driver as a module, choose M Here: the module
will be called pwm-brcmstb.c.
+config PWM_CLK
+ tristate "Clock based PWM support"
+ depends on HAVE_CLK || COMPILE_TEST
+ help
+ Generic PWM framework driver for outputs that can be
+ muxed to clocks.
+
+ To compile this driver as a module, choose M here: the module
+ will be called pwm-clk.
+
config PWM_CLPS711X
tristate "CLPS711X PWM support"
depends on ARCH_CLPS711X || COMPILE_TEST
diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
index 5c08bdb817b4..7bf1a29f02b8 100644
--- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile
@@ -10,6 +10,7 @@ obj-$(CONFIG_PWM_BCM_KONA) += pwm-bcm-kona.o
obj-$(CONFIG_PWM_BCM2835) += pwm-bcm2835.o
obj-$(CONFIG_PWM_BERLIN) += pwm-berlin.o
obj-$(CONFIG_PWM_BRCMSTB) += pwm-brcmstb.o
+obj-$(CONFIG_PWM_CLK) += pwm-clk.o
obj-$(CONFIG_PWM_CLPS711X) += pwm-clps711x.o
obj-$(CONFIG_PWM_CRC) += pwm-crc.o
obj-$(CONFIG_PWM_CROS_EC) += pwm-cros-ec.o
diff --git a/drivers/pwm/pwm-clk.c b/drivers/pwm/pwm-clk.c
new file mode 100644
index 000000000000..c2a503d684a7
--- /dev/null
+++ b/drivers/pwm/pwm-clk.c
@@ -0,0 +1,148 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Clock based PWM controller
+ *
+ * Copyright (c) 2021 Nikita Travkin <nikita@xxxxxxx>
+ *
+ * This is an "adapter" driver that allows PWM consumers to use
+ * system clocks with duty cycle control as PWM outputs.
+ *
+ * Limitations:
+ * - Due to the fact that exact behavior depends on the underlying
+ * clock driver, various limitations are possible.
+ * - Underlying clock may not be able to give 0% or 100% duty cycle
+ * (constant off or on), exact behavior will depend on the clock.
+ * - When the PWM is disabled, the clock will be disabled as well,
+ * line state will depend on the clock.
+ * - The clk API doesn't expose the necessary calls to implement
+ * .get_state().
+ */
+
+#include <linux/kernel.h>
+#include <linux/math64.h>
+#include <linux/err.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/clk.h>
+#include <linux/pwm.h>
+
+struct pwm_clk_chip {
+ struct pwm_chip chip;
+ struct clk *clk;
+ bool clk_enabled;
+};
+
+#define to_pwm_clk_chip(_chip) container_of(_chip, struct pwm_clk_chip, chip)
+
+static int pwm_clk_apply(struct pwm_chip *chip, struct pwm_device *pwm,
+ const struct pwm_state *state)
+{
+ struct pwm_clk_chip *pcchip = to_pwm_clk_chip(chip);
+ int ret;
+ u32 rate;
+ u64 period = state->period;
+ u64 duty_cycle = state->duty_cycle;
+
+ if (!state->enabled) {
+ if (pwm->state.enabled) {
+ clk_disable(pcchip->clk);
+ pcchip->clk_enabled = false;
+ }
+ return 0;
+ } else if (!pwm->state.enabled) {
+ ret = clk_enable(pcchip->clk);
+ if (ret)
+ return ret;
+ pcchip->clk_enabled = true;
+ }
+
+ /*
+ * We have to enable the clk before setting the rate and duty_cycle,
+ * that however results in a window where the clk is on with a
+ * (potentially) different setting. Also setting period and duty_cycle
+ * are two separate calls, so that probably isn't atomic either.
+ */
+
+ rate = DIV64_U64_ROUND_UP(NSEC_PER_SEC, period);
+ ret = clk_set_rate(pcchip->clk, rate);
+ if (ret)
+ return ret;
+
+ if (state->polarity == PWM_POLARITY_INVERSED)
+ duty_cycle = period - duty_cycle;
+
+ return clk_set_duty_cycle(pcchip->clk, duty_cycle, period);
+}
+
+static const struct pwm_ops pwm_clk_ops = {
+ .apply = pwm_clk_apply,
+ .owner = THIS_MODULE,
+};
+
+static int pwm_clk_probe(struct platform_device *pdev)
+{
+ struct pwm_clk_chip *pcchip;
+ int ret;
+
+ pcchip = devm_kzalloc(&pdev->dev, sizeof(*pcchip), GFP_KERNEL);
+ if (!pcchip)
+ return -ENOMEM;
+
+ pcchip->clk = devm_clk_get(&pdev->dev, NULL);
+ if (IS_ERR(pcchip->clk))
+ return dev_err_probe(&pdev->dev, PTR_ERR(pcchip->clk),
+ "Failed to get clock\n");
+
+ pcchip->chip.dev = &pdev->dev;
+ pcchip->chip.ops = &pwm_clk_ops;
+ pcchip->chip.npwm = 1;
+
+ ret = clk_prepare(pcchip->clk);
+ if (ret < 0)
+ return dev_err_probe(&pdev->dev, ret, "Failed to prepare clock\n");
+
+ ret = pwmchip_add(&pcchip->chip);
+ if (ret < 0) {
+ clk_unprepare(pcchip->clk);
+ return dev_err_probe(&pdev->dev, ret, "Failed to add pwm chip\n");
+ }
+
+ platform_set_drvdata(pdev, pcchip);
+ return 0;
+}
+
+static int pwm_clk_remove(struct platform_device *pdev)
+{
+ struct pwm_clk_chip *pcchip = platform_get_drvdata(pdev);
+
+ pwmchip_remove(&pcchip->chip);
+
+ if (pcchip->clk_enabled)
+ clk_disable(pcchip->clk);
+
+ clk_unprepare(pcchip->clk);
+
+ return 0;
+}
+
+static const struct of_device_id pwm_clk_dt_ids[] = {
+ { .compatible = "clk-pwm", },
+ { /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, pwm_clk_dt_ids);
+
+static struct platform_driver pwm_clk_driver = {
+ .driver = {
+ .name = "pwm-clk",
+ .of_match_table = pwm_clk_dt_ids,
+ },
+ .probe = pwm_clk_probe,
+ .remove = pwm_clk_remove,
+};
+module_platform_driver(pwm_clk_driver);
+
+MODULE_ALIAS("platform:pwm-clk");
+MODULE_AUTHOR("Nikita Travkin <nikita@xxxxxxx>");
+MODULE_DESCRIPTION("Clock based PWM driver");
+MODULE_LICENSE("GPL");
--
2.35.3
