[PATCH v8 0/2] Clock based PWM output driver

[PATCH v8 0/2] Clock based PWM output driver

[Nikita Travkin]

This series introduces an "adapter" driver that allows PWM consumers
to control clock outputs with duty-cycle control.

Some platforms (e.g. some Qualcomm chipsets) have "General Purpose"
clocks that can be muxed to GPIO outputs and used as PWM outputs.
Those outputs may be connected to various peripherals such as
leds in display backlight or haptic feedback motor driver.

To avoid re-implementing every single PWM consumer driver with clk
support (like in [1]) and don't put the burden of providing the PWM
sources on the clock drivers (as was proposed in [2]), clk based
pwm controller driver is introduced.

There is an existing driver that provides the opposite function
in drivers/clk/clk-pwm.c with a compatible "pwm-clock" so the new
driver uses the opposite naming scheme: drivers/pwm/pwm-clk.c
and compatible "clk-pwm".

Changes in v2:
 - Fix filename in the DT schema.
 - Address Uwe's review comments.
Changes in v3:
 - Fix node pattern in the core pwm schema.
 - Address Uwe's review comments.
Changes in v4:
 - Drop the (incorrect) pwm schema change.
 - Use generic node name in the dt bindings example.
Changes in v5:
 - Correct required properties.
 - add missed returns.
Changes in v6:
 - Add missed error cleanup
 - Adjust limitations comment
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

Nikita Travkin (2):
  dt-bindings: pwm: Document clk based PWM controller
  pwm: Add clock based PWM output driver

 .../devicetree/bindings/pwm/clk-pwm.yaml      |  46 ++++++
 drivers/pwm/Kconfig                           |  10 ++
 drivers/pwm/Makefile                          |   1 +
 drivers/pwm/pwm-clk.c                         | 148 ++++++++++++++++++
 4 files changed, 205 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/pwm/clk-pwm.yaml
 create mode 100644 drivers/pwm/pwm-clk.c

-- 
2.35.3

[PATCH v8 1/2] dt-bindings: pwm: Document clk based PWM controller

[Nikita Travkin]

Add YAML devicetree binding for clk based PWM controller

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Nikita Travkin <nikita@trvn.ru>
--
Changes in v2:
 - fix the file name.
Changes in v4:
 - Use generic node name in the dt bindings example.
Changes in v5:
 - make compatible required
---
 .../devicetree/bindings/pwm/clk-pwm.yaml      | 46 +++++++++++++++++++
 1 file changed, 46 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/pwm/clk-pwm.yaml

diff --git a/Documentation/devicetree/bindings/pwm/clk-pwm.yaml b/Documentation/devicetree/bindings/pwm/clk-pwm.yaml
new file mode 100644
index 000000000000..ec1768291503
--- /dev/null
+++ b/Documentation/devicetree/bindings/pwm/clk-pwm.yaml
@@ -0,0 +1,46 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/pwm/clk-pwm.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Clock based PWM controller
+
+maintainers:
+  - Nikita Travkin <nikita@trvn.ru>
+
+description: |
+  Some systems have clocks that can be exposed to external devices.
+  (e.g. by muxing them to GPIO pins)
+  It's often possible to control duty-cycle of such clocks which makes them
+  suitable for generating PWM signal.
+
+allOf:
+  - $ref: pwm.yaml#
+
+properties:
+  compatible:
+    const: clk-pwm
+
+  clocks:
+    description: Clock used to generate the signal.
+    maxItems: 1
+
+  "#pwm-cells":
+    const: 2
+
+unevaluatedProperties: false
+
+required:
+  - compatible
+  - clocks
+
+examples:
+  - |
+    pwm {
+      compatible = "clk-pwm";
+      #pwm-cells = <2>;
+      clocks = <&gcc 0>;
+      pinctrl-names = "default";
+      pinctrl-0 = <&pwm_clk_flash_default>;
+    };
-- 
2.35.3

[PATCH v8 2/2] pwm: Add clock based PWM output driver

[Nikita Travkin]

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@trvn.ru>
--

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@trvn.ru>
+ *
+ * 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@trvn.ru>");
+MODULE_DESCRIPTION("Clock based PWM driver");
+MODULE_LICENSE("GPL");
-- 
2.35.3

Re: [PATCH v8 2/2] pwm: Add clock based PWM output driver

[Uwe Kleine-König]

[-- Attachment #1: Type: text/plain, Size: 716 bytes --]

On Mon, Jul 11, 2022 at 11:23:30AM +0500, Nikita Travkin wrote:
> 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@trvn.ru>

Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

Thanks
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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Re: [PATCH v8 1/2] dt-bindings: pwm: Document clk based PWM controller

[Krzysztof Kozlowski]

On 11/07/2022 08:23, Nikita Travkin wrote:
> Add YAML devicetree binding for clk based PWM controller
> 
> Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
> Reviewed-by: Rob Herring <robh@kernel.org>
> Signed-off-by: Nikita Travkin <nikita@trvn.ru>
> --

This is not correct marker.  You miss blank line before it and it should
be '---'.

> Changes in v2:
>  - fix the file name.
> Changes in v4:
>  - Use generic node name in the dt bindings example.
> Changes in v5:
>  - make compatible required
> ---

Best regards,
Krzysztof

Re: [PATCH v8 2/2] pwm: Add clock based PWM output driver

[Krzysztof Kozlowski]

On 11/07/2022 08:23, Nikita Travkin wrote:
> 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@trvn.ru>
> --
> 

Also not correct patch.

Best regards,
Krzysztof