media: sun6i-csi: Add capture state using vsync for page flip

The current implementation requires up to 3 buffers to properly
implement page flipping without losing frames: one is configured
before the video stream is started, one just after that and page
flipping is synchronized to the frame done interrupt. The comment in
the code mentions that "CSI will lookup the next dma buffer for next
frame before the current frame done IRQ triggered".

Based on observations of the CSI unit behavior, it seems that the
buffer DMA address is sampled when the frame scan begins (in addition
to starting the stream), which corresponds to the vblank interrupt
that hits just before the frame-done interrupt of the previous frame.

As a result, the address configured at the frame done interrupt is not
actually used for the next frame but for the one after that.

This proposal changes the page flipping sync point to the vsync
interrupt, which allows the DMA address to be sampled for the next
frame instead and allows operating with only two buffers.

In addition to the change in the sync point, the code is refactored
to introduce a notion of state that clarifies tracking of the buffers
with tidy functions.
Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c

@@ -566,6 +566,7 @@ void sun6i_csi_set_stream(struct sun6i_csi_device *csi_dev, bool enable)
 
 	regmap_write(regmap, CSI_CH_INT_STA_REG, 0xFF);
 	regmap_write(regmap, CSI_CH_INT_EN_REG,
+		     CSI_CH_INT_EN_VS_INT_EN |
 		     CSI_CH_INT_EN_HB_OF_INT_EN |
 		     CSI_CH_INT_EN_FIFO2_OF_INT_EN |
 		     CSI_CH_INT_EN_FIFO1_OF_INT_EN |
@@ -664,6 +665,9 @@ static irqreturn_t sun6i_csi_interrupt(int irq, void *private)
 	if (status & CSI_CH_INT_STA_FD_PD)
 		sun6i_csi_capture_frame_done(csi_dev);
 
+	if (status & CSI_CH_INT_STA_VS_PD)
+		sun6i_csi_capture_sync(csi_dev);
+
 	regmap_write(regmap, CSI_CH_INT_STA_REG, status);
 
 	return IRQ_HANDLED;

drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.h

@@ -25,9 +25,6 @@ enum sun6i_csi_port {
 struct sun6i_csi_buffer {
 	struct vb2_v4l2_buffer		v4l2_buffer;
 	struct list_head		list;
-
-	dma_addr_t			dma_addr;
-	bool				queued_to_csi;
 };
 
 /**

drivers/media/platform/sunxi/sun6i-csi/sun6i_csi_capture.h

@@ -13,23 +13,34 @@
 
 struct sun6i_csi_device;
 
+#undef current
+struct sun6i_csi_capture_state {
+	struct list_head		queue;
+	spinlock_t			lock; /* Queue and buffers lock. */
+
+	struct sun6i_csi_buffer		*pending;
+	struct sun6i_csi_buffer		*current;
+	struct sun6i_csi_buffer		*complete;
+
+	unsigned int			sequence;
+};
+
 struct sun6i_csi_capture {
+	struct sun6i_csi_capture_state	state;
+
 	struct video_device		video_dev;
 	struct vb2_queue		queue;
 	struct mutex			lock; /* Queue lock. */
 	struct media_pad		pad;
 
-	struct list_head		dma_queue;
-	spinlock_t			dma_queue_lock; /* DMA queue lock. */
-
 	struct v4l2_format		format;
 	u32				mbus_code;
-	unsigned int			sequence;
 };
 
+void sun6i_csi_capture_sync(struct sun6i_csi_device *csi_dev);
+void sun6i_csi_capture_frame_done(struct sun6i_csi_device *csi_dev);
+
 int sun6i_csi_capture_setup(struct sun6i_csi_device *csi_dev);
 void sun6i_csi_capture_cleanup(struct sun6i_csi_device *csi_dev);
 
-void sun6i_csi_capture_frame_done(struct sun6i_csi_device *csi_dev);
-
 #endif /* __SUN6I_CAPTURE_H__ */