[PATCH 01/14] media: qcom: camss: Introduce CPU latency QoS during streaming

[bryan.odonoghue@linaro.org]

From: Bryan O'Donoghue <bryan.odonoghue@linaro.org>

On a quiescent system - for example the X1 CRD booted to a simple ramdisk
rootfs during development of V4L2_EVENT_FRAME_SYNC it was observed that
interrupt for buffer done could be delayed until after the SOF for the next
frame.

Fiddling about with the interrupt bits, clearing them and changing the
logic of V4L2_EVENT_FRAME_SYNC to buffer completion didn't work and besides
"felt wrong".

Tracing it looks like this:
<idle>-0       [000] d.h1.    36.374380: csid_isr: rdi0 sof=1 done=0
<idle>-0       [000] d.h1.    36.406601: csid_isr: rdi0 sof=1 done=1
<idle>-0       [000] d.h1.    36.439910: csid_isr: rdi0 sof=1 done=1
<idle>-0       [000] d.h1.    36.473245: csid_isr: rdi0 sof=1 done=1
<idle>-0       [000] d.h1.    36.504786: csid_isr: rdi0 sof=0 done=1
<idle>-0       [000] d.h1.    36.506350: csid_isr: rdi0 sof=1 done=0

Tracing with /dev/cpu_dma_latency = 0 looks like this:
<idle>-0       [000] d.h1.   556.149115: csid_isr: rdi0 sof=1 done=0
<idle>-0       [000] d.h1.   556.181338: csid_isr: rdi0 sof=0 done=1
<idle>-0       [000] d.h1.   556.182880: csid_isr: rdi0 sof=1 done=0
<idle>-0       [000] d.h1.   556.214643: csid_isr: rdi0 sof=0 done=1
<idle>-0       [000] d.h1.   556.216185: csid_isr: rdi0 sof=1 done=0

The second is the pattern you expect CSI SOF followed by data.

We will require SOF to track and understand which data-frame is correlated
to which camera stastics and parameters frame. On an ordinary system with
several things pinging off at once, WiFi, display, keyboard you will be
unlikely to hit deep idle and hence unlikely to see the long exit. However
we should design for the case where the system is otherwise quiescent with
only the camera streaming.

Choosing a request of 300us - 1000us seemed to work fine but cutting the
margin finer, similar to the value on IPU6.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
---
 drivers/media/platform/qcom/camss/camss-video.c |  4 ++++
 drivers/media/platform/qcom/camss/camss.c       | 27 +++++++++++++++++++++++++
 drivers/media/platform/qcom/camss/camss.h       |  7 +++++++
 3 files changed, 38 insertions(+)

diff --git a/drivers/media/platform/qcom/camss/camss-video.c b/drivers/media/platform/qcom/camss/camss-video.c
index 0852eb6f13154..191cb71d02e19 100644
--- a/drivers/media/platform/qcom/camss/camss-video.c
+++ b/drivers/media/platform/qcom/camss/camss-video.c
@@ -286,6 +286,8 @@ static int video_start_streaming(struct vb2_queue *q, unsigned int count)
 			goto error;
 	}
 
+	camss_cpu_latency_get(video->camss);
+
 	return 0;
 
 error:
@@ -306,6 +308,8 @@ static void video_stop_streaming(struct vb2_queue *q)
 	struct v4l2_subdev *subdev;
 	int ret;
 
+	camss_cpu_latency_put(video->camss);
+
 	entity = &vdev->entity;
 	while (1) {
 		pad = &entity->pads[0];
diff --git a/drivers/media/platform/qcom/camss/camss.c b/drivers/media/platform/qcom/camss/camss.c
index c54185c93a8a9..06e1bf82f4836 100644
--- a/drivers/media/platform/qcom/camss/camss.c
+++ b/drivers/media/platform/qcom/camss/camss.c
@@ -5064,6 +5064,29 @@ void camss_buf_done(struct camss *camss, int hw_id, int port_id)
 	}
 }
 
+#define CAMSS_CPU_LATENCY_US	300
+
+void camss_cpu_latency_get(struct camss *camss)
+{
+	mutex_lock(&camss->cpu_latency_lock);
+
+	if (camss->cpu_latency_users++ == 0)
+		cpu_latency_qos_add_request(&camss->cpu_latency,
+					    CAMSS_CPU_LATENCY_US);
+
+	mutex_unlock(&camss->cpu_latency_lock);
+}
+
+void camss_cpu_latency_put(struct camss *camss)
+{
+	mutex_lock(&camss->cpu_latency_lock);
+
+	if (--camss->cpu_latency_users == 0)
+		cpu_latency_qos_remove_request(&camss->cpu_latency);
+
+	mutex_unlock(&camss->cpu_latency_lock);
+}
+
 /*
  * camss_register_entities - Register subdev nodes and create links
  * @camss: CAMSS device
@@ -5429,6 +5452,10 @@ static int camss_probe(struct platform_device *pdev)
 	camss->dev = dev;
 	platform_set_drvdata(pdev, camss);
 
+	ret = devm_mutex_init(dev, &camss->cpu_latency_lock);
+	if (ret)
+		return ret;
+
 	camss->csiphy = devm_kcalloc(dev, camss->res->csiphy_num,
 				     sizeof(*camss->csiphy), GFP_KERNEL);
 	if (!camss->csiphy)
diff --git a/drivers/media/platform/qcom/camss/camss.h b/drivers/media/platform/qcom/camss/camss.h
index 7dc2fd9f03e0d..9341fdc9bca0e 100644
--- a/drivers/media/platform/qcom/camss/camss.h
+++ b/drivers/media/platform/qcom/camss/camss.h
@@ -11,6 +11,8 @@
 #define QC_MSM_CAMSS_H
 
 #include <linux/device.h>
+#include <linux/mutex.h>
+#include <linux/pm_qos.h>
 #include <linux/types.h>
 #include <media/v4l2-async.h>
 #include <media/v4l2-device.h>
@@ -141,6 +143,9 @@ struct camss {
 	struct icc_path *icc_path[ICC_SM8250_COUNT];
 	const struct camss_resources *res;
 	bool legacy_phy;
+	struct mutex cpu_latency_lock;	/* Guards cpu_latency_users */
+	unsigned int cpu_latency_users;
+	struct pm_qos_request cpu_latency;
 };
 
 struct camss_camera_interface {
@@ -182,5 +187,7 @@ void camss_delete(struct camss *camss);
 void camss_buf_done(struct camss *camss, int hw_id, int port_id);
 void camss_reg_update(struct camss *camss, int hw_id,
 		      int port_id, bool is_clear);
+void camss_cpu_latency_get(struct camss *camss);
+void camss_cpu_latency_put(struct camss *camss);
 
 #endif /* QC_MSM_CAMSS_H */

-- 
2.56.0