[PATCH v2 0/3] DCMI set minimum cpufreq requirement

[PATCH v2 0/3] DCMI set minimum cpufreq requirement

[Benjamin Gaignard]

This series allow to STM32 camera interface (DCMI) to require a minimum
frequency to the CPUs before start streaming frames from the sensor.
The minimum frequency requirement is provided in the devide-tree node.

Setting a minimum frequency for the CPUs is needed to ensure a quick handling
of the interrupts between two sensor frames and avoid dropping half of them.

Benjamin Gaignard (3):
  dt-bindings: media: stm32-dcmi: Add DCMI min frequency property
  media: stm32-dcmi: Set minimum cpufreq requirement
  ARM: dts: stm32: Set DCMI frequency requirement for stm32mp15x

 .../devicetree/bindings/media/st,stm32-dcmi.yaml   |  8 ++
 arch/arm/boot/dts/stm32mp151.dtsi                  |  1 +
 drivers/media/platform/stm32/stm32-dcmi.c          | 90 ++++++++++++++++++++--
 3 files changed, 91 insertions(+), 8 deletions(-)

-- 
2.15.0

[PATCH v2 1/3] dt-bindings: media: stm32-dcmi: Add DCMI min frequency property

[Benjamin Gaignard]

Document st,stm32-dcmi-min-frequency property which is used to
request CPUs minimum frequency when streaming frames.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
---
 Documentation/devicetree/bindings/media/st,stm32-dcmi.yaml | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Documentation/devicetree/bindings/media/st,stm32-dcmi.yaml b/Documentation/devicetree/bindings/media/st,stm32-dcmi.yaml
index 3fe778cb5cc3..05ca85a2411a 100644
--- a/Documentation/devicetree/bindings/media/st,stm32-dcmi.yaml
+++ b/Documentation/devicetree/bindings/media/st,stm32-dcmi.yaml
@@ -44,6 +44,13 @@ properties:
       bindings defined in
       Documentation/devicetree/bindings/media/video-interfaces.txt.
 
+  st,stm32-dcmi-min-frequency:
+    description: DCMI minimum CPUs frequency requirement (in KHz).
+    allOf:
+      - $ref: /schemas/types.yaml#/definitions/uint32
+      - minimum: 0
+      - default: 0
+
 required:
   - compatible
   - reg
@@ -71,6 +78,7 @@ examples:
         clock-names = "mclk";
         dmas = <&dmamux1 75 0x400 0x0d>;
         dma-names = "tx";
+        st,stm32-dcmi-min-frequency = <650000>;
 
         port {
              dcmi_0: endpoint {
-- 
2.15.0

[PATCH v2 2/3] media: stm32-dcmi: Set minimum cpufreq requirement

[Benjamin Gaignard]

Before start streaming set cpufreq minimum frequency requirement.
The cpufreq governor will adapt the frequencies and we will have
no latency for handling interrupts.
The frequency requirement is retrieved from the device-tree node.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
---
 drivers/media/platform/stm32/stm32-dcmi.c | 90 ++++++++++++++++++++++++++++---
 1 file changed, 82 insertions(+), 8 deletions(-)

diff --git a/drivers/media/platform/stm32/stm32-dcmi.c b/drivers/media/platform/stm32/stm32-dcmi.c
index b8931490b83b..1b9f24986694 100644
--- a/drivers/media/platform/stm32/stm32-dcmi.c
+++ b/drivers/media/platform/stm32/stm32-dcmi.c
@@ -13,10 +13,12 @@
 
 #include <linux/clk.h>
 #include <linux/completion.h>
+#include <linux/cpufreq.h>
 #include <linux/delay.h>
 #include <linux/dmaengine.h>
 #include <linux/init.h>
 #include <linux/interrupt.h>
+#include <linux/irq.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/of.h>
@@ -99,6 +101,9 @@ enum state {
 
 #define OVERRUN_ERROR_THRESHOLD	3
 
+static DEFINE_PER_CPU(struct cpufreq_policy *, policy);
+static DEFINE_PER_CPU(struct freq_qos_request, qos_req);
+
 struct dcmi_graph_entity {
 	struct v4l2_async_subdev asd;
 
@@ -133,6 +138,7 @@ struct stm32_dcmi {
 	struct resource			*res;
 	struct reset_control		*rstc;
 	int				sequence;
+	int				irq;
 	struct list_head		buffers;
 	struct dcmi_buf			*active;
 
@@ -173,6 +179,8 @@ struct stm32_dcmi {
 	struct media_device		mdev;
 	struct media_pad		vid_cap_pad;
 	struct media_pipeline		pipeline;
+
+	u32				min_frequency;
 };
 
 static inline struct stm32_dcmi *notifier_to_dcmi(struct v4l2_async_notifier *n)
@@ -722,6 +730,62 @@ static void dcmi_pipeline_stop(struct stm32_dcmi *dcmi)
 	dcmi_pipeline_s_stream(dcmi, 0);
 }
 
+static void dcmi_get_min_frequency(struct stm32_dcmi *dcmi)
+{
+	struct device_node *np = dcmi->mdev.dev->of_node;
+
+	dcmi->min_frequency = FREQ_QOS_MIN_DEFAULT_VALUE;
+
+	of_property_read_u32(np, "st,stm32-dcmi-min-frequency",
+			     &dcmi->min_frequency);
+}
+
+static void dcmi_get_cpu_policy(struct stm32_dcmi *dcmi)
+{
+	struct cpufreq_policy *p;
+	int cpu;
+
+	for_each_cpu(cpu, irq_get_affinity_mask(dcmi->irq)) {
+		p = cpufreq_cpu_get(cpu);
+		if (!p)
+			continue;
+
+		freq_qos_add_request(&p->constraints, &per_cpu(qos_req, cpu),
+				     FREQ_QOS_MIN, FREQ_QOS_MIN_DEFAULT_VALUE);
+
+		per_cpu(policy, cpu) = p;
+	}
+}
+
+static void dcmi_put_cpu_policy(struct stm32_dcmi *dcmi)
+{
+	struct cpufreq_policy *p;
+	int cpu;
+
+	for_each_cpu(cpu, irq_get_affinity_mask(dcmi->irq)) {
+		p = per_cpu(policy, cpu);
+		if (!p)
+			continue;
+
+		freq_qos_remove_request(&per_cpu(qos_req, cpu));
+		cpufreq_cpu_put(p);
+	}
+}
+
+static void dcmi_set_min_frequency(struct stm32_dcmi *dcmi, u64 freq)
+{
+	struct cpufreq_policy *p;
+	int cpu;
+
+	for_each_cpu(cpu, irq_get_affinity_mask(dcmi->irq)) {
+		p = per_cpu(policy, cpu);
+		if (!p)
+			continue;
+
+		freq_qos_update_request(&per_cpu(qos_req, cpu), freq);
+	}
+}
+
 static int dcmi_start_streaming(struct vb2_queue *vq, unsigned int count)
 {
 	struct stm32_dcmi *dcmi = vb2_get_drv_priv(vq);
@@ -736,11 +800,13 @@ static int dcmi_start_streaming(struct vb2_queue *vq, unsigned int count)
 		goto err_release_buffers;
 	}
 
+	dcmi_set_min_frequency(dcmi, dcmi->min_frequency);
+
 	ret = media_pipeline_start(&dcmi->vdev->entity, &dcmi->pipeline);
 	if (ret < 0) {
 		dev_err(dcmi->dev, "%s: Failed to start streaming, media pipeline start error (%d)\n",
 			__func__, ret);
-		goto err_pm_put;
+		goto err_drop_qos;
 	}
 
 	ret = dcmi_pipeline_start(dcmi);
@@ -835,7 +901,8 @@ static int dcmi_start_streaming(struct vb2_queue *vq, unsigned int count)
 err_media_pipeline_stop:
 	media_pipeline_stop(&dcmi->vdev->entity);
 
-err_pm_put:
+err_drop_qos:
+	dcmi_set_min_frequency(dcmi, FREQ_QOS_MIN_DEFAULT_VALUE);
 	pm_runtime_put(dcmi->dev);
 
 err_release_buffers:
@@ -863,6 +930,8 @@ static void dcmi_stop_streaming(struct vb2_queue *vq)
 
 	media_pipeline_stop(&dcmi->vdev->entity);
 
+	dcmi_set_min_frequency(dcmi, FREQ_QOS_MIN_DEFAULT_VALUE);
+
 	spin_lock_irq(&dcmi->irqlock);
 
 	/* Disable interruptions */
@@ -1838,7 +1907,6 @@ static int dcmi_probe(struct platform_device *pdev)
 	struct vb2_queue *q;
 	struct dma_chan *chan;
 	struct clk *mclk;
-	int irq;
 	int ret = 0;
 
 	match = of_match_device(of_match_ptr(stm32_dcmi_of_match), &pdev->dev);
@@ -1879,9 +1947,9 @@ static int dcmi_probe(struct platform_device *pdev)
 	dcmi->bus.bus_width = ep.bus.parallel.bus_width;
 	dcmi->bus.data_shift = ep.bus.parallel.data_shift;
 
-	irq = platform_get_irq(pdev, 0);
-	if (irq <= 0)
-		return irq ? irq : -ENXIO;
+	dcmi->irq = platform_get_irq(pdev, 0);
+	if (dcmi->irq <= 0)
+		return dcmi->irq ? dcmi->irq : -ENXIO;
 
 	dcmi->res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	if (!dcmi->res) {
@@ -1895,11 +1963,12 @@ static int dcmi_probe(struct platform_device *pdev)
 		return PTR_ERR(dcmi->regs);
 	}
 
-	ret = devm_request_threaded_irq(&pdev->dev, irq, dcmi_irq_callback,
+	ret = devm_request_threaded_irq(&pdev->dev, dcmi->irq,
+					dcmi_irq_callback,
 					dcmi_irq_thread, IRQF_ONESHOT,
 					dev_name(&pdev->dev), dcmi);
 	if (ret) {
-		dev_err(&pdev->dev, "Unable to request irq %d\n", irq);
+		dev_err(&pdev->dev, "Unable to request irq %d\n", dcmi->irq);
 		return ret;
 	}
 
@@ -2022,6 +2091,9 @@ static int dcmi_probe(struct platform_device *pdev)
 
 	dev_info(&pdev->dev, "Probe done\n");
 
+	dcmi_get_min_frequency(dcmi);
+	dcmi_get_cpu_policy(dcmi);
+
 	platform_set_drvdata(pdev, dcmi);
 
 	pm_runtime_enable(&pdev->dev);
@@ -2049,6 +2121,8 @@ static int dcmi_remove(struct platform_device *pdev)
 
 	pm_runtime_disable(&pdev->dev);
 
+	dcmi_put_cpu_policy(dcmi);
+
 	v4l2_async_notifier_unregister(&dcmi->notifier);
 	v4l2_async_notifier_cleanup(&dcmi->notifier);
 	media_entity_cleanup(&dcmi->vdev->entity);
-- 
2.15.0

[PATCH v2 3/3] ARM: dts: stm32: Set DCMI frequency requirement for stm32mp15x

[Benjamin Gaignard]

Make sure that CPUs will at least run at 650Mhz when streaming
sensor frames.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
---
 arch/arm/boot/dts/stm32mp151.dtsi | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm/boot/dts/stm32mp151.dtsi b/arch/arm/boot/dts/stm32mp151.dtsi
index 3ea05ba48215..f6d7bf4f8231 100644
--- a/arch/arm/boot/dts/stm32mp151.dtsi
+++ b/arch/arm/boot/dts/stm32mp151.dtsi
@@ -1091,6 +1091,7 @@
 			clock-names = "mclk";
 			dmas = <&dmamux1 75 0x400 0x0d>;
 			dma-names = "tx";
+			st,stm32-dcmi-min-frequency = <650000>;
 			status = "disabled";
 		};
 
-- 
2.15.0

Re: [PATCH v2 2/3] media: stm32-dcmi: Set minimum cpufreq requirement

[Valentin Schneider]

On 03/06/20 13:45, Benjamin Gaignard wrote:
> +static void dcmi_set_min_frequency(struct stm32_dcmi *dcmi, u64 freq)
> +{
> +	struct cpufreq_policy *p;
> +	int cpu;
> +
> +	for_each_cpu(cpu, irq_get_affinity_mask(dcmi->irq)) {
> +		p = per_cpu(policy, cpu);
> +		if (!p)
> +			continue;
> +
> +		freq_qos_update_request(&per_cpu(qos_req, cpu), freq);
> +	}
> +}
> +

You may want to use a "visited" cpumask as I suggested in the previous
thread, since a policy can cover more than one CPU (IOW, a frequency domain
can span more than one CPU). It's not required per-se, AFAICT, but it makes
things a bit neater.

I also think you'll have to use the affinity notifier
(irq_set_affinity_notifier()), since AFAICT userspace can change the
affinity of that IRQ. I suppose you'll want something like:
- Check if we currently are in streaming mode
- Clear the QoS request for CPUs that were previously boosted but that
  aren't in the new mask
- Add the request for the new CPUs.

You'll probably need serialize the reading of the mask in the regular
dcmi_set_min_frequency() as well. I concur all of that is somewhat
annoying, but AFAICT that's required for a sturdy implementation.

>  static int dcmi_start_streaming(struct vb2_queue *vq, unsigned int count)
>  {
>       struct stm32_dcmi *dcmi = vb2_get_drv_priv(vq);