[RFC 3/3] media: stm32-dcmi: Inform cpufreq governors about cpu load needs

From: Benjamin Gaignard
Date: Tue May 26 2020 - 11:17:20 EST

When start streaming the CPU load could remain very low because almost
all the capture pipeline is done in hardware (i.e. without using the CPU)
and let believe to cpufreq governor that it could use lower frequencies.
If the governor decides to use a too low frequency that becomes a problem
when we need to acknowledge the interrupt during the blanking time.

To avoid this problem, DCMI driver informs the cpufreq governors by adding
a cpufreq minimum load QoS resquest.

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

diff --git a/drivers/media/platform/stm32/stm32-dcmi.c b/drivers/media/platform/stm32/stm32-dcmi.c
index b8931490b83b..774f2506b2f1 100644
--- a/drivers/media/platform/stm32/stm32-dcmi.c
+++ b/drivers/media/platform/stm32/stm32-dcmi.c
@@ -24,6 +24,7 @@
#include <linux/of_graph.h>
#include <linux/pinctrl/consumer.h>
#include <linux/platform_device.h>
+#include <linux/pm_qos.h>
#include <linux/pm_runtime.h>
#include <linux/reset.h>
#include <linux/videodev2.h>
@@ -173,6 +174,8 @@ struct stm32_dcmi {
struct media_device mdev;
struct media_pad vid_cap_pad;
struct media_pipeline pipeline;
+ struct pm_qos_request qos_request;

static inline struct stm32_dcmi *notifier_to_dcmi(struct v4l2_async_notifier *n)
@@ -827,6 +830,9 @@ static int dcmi_start_streaming(struct vb2_queue *vq, unsigned int count)
reg_set(dcmi->regs, DCMI_IER, IT_OVR | IT_ERR);

+ cpufreq_minload_qos_add_request(&dcmi->qos_request,
return 0;

@@ -859,6 +865,8 @@ static void dcmi_stop_streaming(struct vb2_queue *vq)
struct stm32_dcmi *dcmi = vb2_get_drv_priv(vq);
struct dcmi_buf *buf, *node;

+ cpufreq_minload_qos_remove_request(&dcmi->qos_request);