linux-kernel - Re: [PATCH v5 2/3] media: stm32-dcmi: Set minimum cpufreq requirement

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Date:   Wed, 10 Jun 2020 12:20:02 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Benjamin Gaignard <benjamin.gaignard@...com>
Cc:     hugues.fruchet@...com, mchehab@...nel.org,
        mcoquelin.stm32@...il.com, alexandre.torgue@...com,
        linux-media@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        vincent.guittot@...aro.org, rjw@...ysocki.net
Subject: Re: [PATCH v5 2/3] media: stm32-dcmi: Set minimum cpufreq requirement


Hi Benjamin,

On 09/06/20 12:58, Benjamin Gaignard wrote:
> +static void dcmi_set_min_frequency(struct stm32_dcmi *dcmi, s32 freq)
> +{
> +	struct irq_affinity_notify *notify = &dcmi->notify;
> +	struct cpumask clear;
> +
> +	mutex_lock(&dcmi->freq_lock);
> +	dcmi->targeted_frequency = freq;
> +	mutex_unlock(&dcmi->freq_lock);
> +
> +	if (freq) {
> +		dcmi_irq_notifier_notify(notify,
> +					 irq_get_affinity_mask(dcmi->irq));
> +	} else {
> +		cpumask_clear(&clear);
> +		dcmi_irq_notifier_notify(notify, &clear);
> +	}
> +}
> +

IIUC the changes in this version, you would now need a call to
freq_qos_update_request() in the notifier. That's because you can now go
through the notifier callback with

  targeted_frequency = FREQ_QOS_MIN_DEFAULT_VALUE

yet still add CPUs to the boosted mask. I think you were pretty close to a
decent solution in your previous version, with some notifier registration
movement. This is what I had in mind (the diff is against v4; ofc
absolutely untested!):

---
diff --git a/drivers/media/platform/stm32/stm32-dcmi.c b/drivers/media/platform/stm32/stm32-dcmi.c
index c2389776a958..cc147de6ea70 100644
--- a/drivers/media/platform/stm32/stm32-dcmi.c
+++ b/drivers/media/platform/stm32/stm32-dcmi.c
@@ -801,15 +801,22 @@ static void dcmi_set_min_frequency(struct stm32_dcmi *dcmi, s32 freq)
        struct irq_affinity_notify *notify = &dcmi->notify;

        if (freq) {
+		/*
+		 * Register the notifier before doing any change, so the
+		 * callback can be queued if an affinity change happens *while*
+		 * we are requesting the boosts.
+		 */
+		irq_set_affinity_notifier(dcmi->irq, notify);
                dcmi_irq_notifier_notify(notify,
                                         irq_get_affinity_mask(dcmi->irq));
-
-		notify->notify = dcmi_irq_notifier_notify;
-		notify->release = dcmi_irq_notifier_release;
-		irq_set_affinity_notifier(dcmi->irq, notify);
        } else {
                struct cpumask clear;

+		/*
+		 * Unregister the notifier before clearing the boost requests,
+		 * as we don't want to boost again if an affinity change happens
+		 * *while* we are clearing the requests
+		 */
                irq_set_affinity_notifier(dcmi->irq, NULL);
                cpumask_clear(&clear);
                dcmi_irq_notifier_notify(notify, &clear);
@@ -2032,6 +2039,9 @@ static int dcmi_probe(struct platform_device *pdev)
        if (!alloc_cpumask_var(&dcmi->boosted, GFP_KERNEL))
                return -ENODEV;

+	dcmi->notify->notify = dcmi_irq_notifier_notify;
+	dcmi->notify->release = dcmi_irq_notifier_release;
+
        q = &dcmi->queue;

        dcmi->v4l2_dev.mdev = &dcmi->mdev;
---

Does that make sense to you?