linux-kernel - [PATCH v2 1/4] drivers: media: bcm2835-unicam: Improve frame sequence count handling

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Message-Id: <20241127111515.565992-2-naush@raspberrypi.com>
Date: Wed, 27 Nov 2024 11:15:12 +0000
From: Naushir Patuck <naush@...pberrypi.com>
To: Raspberry Pi Kernel Maintenance <kernel-list@...pberrypi.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	Ray Jui <rjui@...adcom.com>,
	Scott Branden <sbranden@...adcom.com>
Cc: linux-media@...r.kernel.org,
	linux-rpi-kernel@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	jacopo.mondi@...asonboard.com,
	Dave Stevenson <dave.stevenson@...pberrypi.com>,
	Naushir Patuck <naush@...pberrypi.com>
Subject: [PATCH v2 1/4] drivers: media: bcm2835-unicam: Improve frame sequence count handling

Ensure that the frame sequence counter is incremented only if a previous
frame start interrupt has occurred, or a frame start + frame end has
occurred simultaneously.

This corresponds the sequence number with the actual number of frames
produced by the sensor, not the number of frame buffers dequeued back
to userland.

Signed-off-by: Naushir Patuck <naush@...pberrypi.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@...asonboard.com>
---
 .../media/platform/broadcom/bcm2835-unicam.c  | 22 +++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/drivers/media/platform/broadcom/bcm2835-unicam.c b/drivers/media/platform/broadcom/bcm2835-unicam.c
index 3aed0e493c81..36fb186a0421 100644
--- a/drivers/media/platform/broadcom/bcm2835-unicam.c
+++ b/drivers/media/platform/broadcom/bcm2835-unicam.c
@@ -199,6 +199,7 @@ struct unicam_device {
 	/* subdevice async notifier */
 	struct v4l2_async_notifier notifier;
 	unsigned int sequence;
+	bool frame_started;
 
 	/* Sensor node */
 	struct {
@@ -742,6 +743,8 @@ static irqreturn_t unicam_isr(int irq, void *dev)
 	 * buffer forever.
 	 */
 	if (fe) {
+		bool inc_seq = unicam->frame_started;
+
 		/*
 		 * Ensure we have swapped buffers already as we can't
 		 * stop the peripheral. If no buffer is available, use a
@@ -761,11 +764,24 @@ static irqreturn_t unicam_isr(int irq, void *dev)
 			 * + FS + LS). In this case, we cannot signal the buffer
 			 * as complete, as the HW will reuse that buffer.
 			 */
-			if (node->cur_frm && node->cur_frm != node->next_frm)
+			if (node->cur_frm && node->cur_frm != node->next_frm) {
 				unicam_process_buffer_complete(node, sequence);
+				inc_seq = true;
+			}
 			node->cur_frm = node->next_frm;
 		}
-		unicam->sequence++;
+
+		/*
+		 * Increment the sequence number conditionally on either a FS
+		 * having already occurred, or in the FE + FS condition as
+		 * caught in the FE handler above. This ensures the sequence
+		 * number corresponds to the frames generated by the sensor, not
+		 * the frames dequeued to userland.
+		 */
+		if (inc_seq) {
+			unicam->sequence++;
+			unicam->frame_started = false;
+		}
 	}
 
 	if (ista & UNICAM_FSI) {
@@ -795,6 +811,7 @@ static irqreturn_t unicam_isr(int irq, void *dev)
 		}
 
 		unicam_queue_event_sof(unicam);
+		unicam->frame_started = true;
 	}
 
 	/*
@@ -1413,6 +1430,7 @@ static int unicam_sd_enable_streams(struct v4l2_subdev *sd,
 		if (unicam->pipe.nodes & BIT(UNICAM_METADATA_NODE))
 			unicam_start_metadata(unicam);
 
+		unicam->frame_started = false;
 		unicam_start_rx(unicam, state);
 	}
 
-- 
2.34.1