Re: [PATCH] media: stm32-dcmi: Set minimum cpufreq requirement

[Hugues FRUCHET <hugues.fruchet@st.com>]

Acked-by: Hugues Fruchet <hugues.fruchet@st.com>

On 5/27/20 5:16 PM, Benjamin Gaignard wrote:
> Before start streaming set cpufreq minimum frequency requirement.
> The cpufreq governor will adapt the frequencies and we will have
> no latency for handling interrupts.
> 
> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
> ---
>   drivers/media/platform/stm32/stm32-dcmi.c | 29 ++++++++++++++++++++++++++++-
>   1 file changed, 28 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/platform/stm32/stm32-dcmi.c b/drivers/media/platform/stm32/stm32-dcmi.c
> index b8931490b83b..97c342351569 100644
> --- a/drivers/media/platform/stm32/stm32-dcmi.c
> +++ b/drivers/media/platform/stm32/stm32-dcmi.c
> @@ -13,6 +13,7 @@
>   
>   #include <linux/clk.h>
>   #include <linux/completion.h>
> +#include <linux/cpufreq.h>
>   #include <linux/delay.h>
>   #include <linux/dmaengine.h>
>   #include <linux/init.h>
> @@ -99,6 +100,8 @@ enum state {
>   
>   #define OVERRUN_ERROR_THRESHOLD	3
>   
> +#define DCMI_MIN_FREQ	650000 /* in KHz */
> +
>   struct dcmi_graph_entity {
>   	struct v4l2_async_subdev asd;
>   
> @@ -173,6 +176,10 @@ struct stm32_dcmi {
>   	struct media_device		mdev;
>   	struct media_pad		vid_cap_pad;
>   	struct media_pipeline		pipeline;
> +
> +	/* CPU freq contraint */
> +	struct cpufreq_policy		*policy;
> +	struct freq_qos_request		qos_req;
>   };
>   
>   static inline struct stm32_dcmi *notifier_to_dcmi(struct v4l2_async_notifier *n)
> @@ -736,11 +743,20 @@ static int dcmi_start_streaming(struct vb2_queue *vq, unsigned int count)
>   		goto err_release_buffers;
>   	}
>   
> +	if (dcmi->policy) {
> +		ret = freq_qos_add_request(&dcmi->policy->constraints,
> +					   &dcmi->qos_req, FREQ_QOS_MIN,
> +					   DCMI_MIN_FREQ);
> +
> +		if (ret < 0)
> +			goto err_pm_put;
> +	}
> +
>   	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);
> @@ -835,6 +851,9 @@ static int dcmi_start_streaming(struct vb2_queue *vq, unsigned int count)
>   err_media_pipeline_stop:
>   	media_pipeline_stop(&dcmi->vdev->entity);
>   
> +err_drop_qos:
> +	if (dcmi->policy)
> +		freq_qos_remove_request(&dcmi->qos_req);
>   err_pm_put:
>   	pm_runtime_put(dcmi->dev);
>   
> @@ -863,6 +882,9 @@ static void dcmi_stop_streaming(struct vb2_queue *vq)
>   
>   	media_pipeline_stop(&dcmi->vdev->entity);
>   
> +	if (dcmi->policy)
> +		freq_qos_remove_request(&dcmi->qos_req);
> +
>   	spin_lock_irq(&dcmi->irqlock);
>   
>   	/* Disable interruptions */
> @@ -2020,6 +2042,8 @@ static int dcmi_probe(struct platform_device *pdev)
>   		goto err_cleanup;
>   	}
>   
> +	dcmi->policy = cpufreq_cpu_get(0);
> +
>   	dev_info(&pdev->dev, "Probe done\n");
>   
>   	platform_set_drvdata(pdev, dcmi);
> @@ -2049,6 +2073,9 @@ static int dcmi_remove(struct platform_device *pdev)
>   
>   	pm_runtime_disable(&pdev->dev);
>   
> +	if (dcmi->policy)
> +		cpufreq_cpu_put(dcmi->policy);
> +
>   	v4l2_async_notifier_unregister(&dcmi->notifier);
>   	v4l2_async_notifier_cleanup(&dcmi->notifier);
>   	media_entity_cleanup(&dcmi->vdev->entity);
>