V4L/DVB (11322): pxa_camera: Fix overrun condition on last buffer

The last buffer queued will often overrun, as the DMA chain
is finished, and the time the dma irq handler is activated,
the QCI fifos are filled by the sensor.

The fix is to ignore the overrun condition on the last
queued buffer, and restart the capture only on intermediate
buffers of the chain.

Moreover, a fix was added to the very unlikely condition
where in YUV422P mode, one channel overruns while another
completes at the very same time. The capture is restarted
after the overrun as before, but the other channel
completion is now ignored.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/pxa_camera.c

@@ -624,6 +624,7 @@ static void pxa_camera_stop_capture(struct pxa_camera_dev *pcdev)
 	cicr0 = __raw_readl(pcdev->base + CICR0) & ~CICR0_ENB;
 	__raw_writel(cicr0, pcdev->base + CICR0);
 
+	pcdev->active = NULL;
 	dev_dbg(pcdev->dev, "%s\n", __func__);
 }
 
@@ -697,7 +698,6 @@ static void pxa_camera_wakeup(struct pxa_camera_dev *pcdev,
 
 	if (list_empty(&pcdev->capture)) {
 		pxa_camera_stop_capture(pcdev);
-		pcdev->active = NULL;
 		for (i = 0; i < pcdev->channels; i++)
 			pcdev->sg_tail[i] = NULL;
 		return;
@@ -765,10 +765,20 @@ static void pxa_camera_dma_irq(int channel, struct pxa_camera_dev *pcdev,
 		goto out;
 	}
 
-	if (!pcdev->active) {
-		dev_err(pcdev->dev, "DMA End IRQ with no active buffer!\n");
+	/*
+	 * pcdev->active should not be NULL in DMA irq handler.
+	 *
+	 * But there is one corner case : if capture was stopped due to an
+	 * overrun of channel 1, and at that same channel 2 was completed.
+	 *
+	 * When handling the overrun in DMA irq for channel 1, we'll stop the
+	 * capture and restart it (and thus set pcdev->active to NULL). But the
+	 * DMA irq handler will already be pending for channel 2. So on entering
+	 * the DMA irq handler for channel 2 there will be no active buffer, yet
+	 * that is normal.
+	 */
+	if (!pcdev->active)
 		goto out;
-	}
 
 	vb = &pcdev->active->vb;
 	buf = container_of(vb, struct pxa_buffer, vb);
@@ -779,7 +789,12 @@ static void pxa_camera_dma_irq(int channel, struct pxa_camera_dev *pcdev,
 		status & DCSR_ENDINTR ? "EOF " : "", vb, DDADR(channel));
 
 	if (status & DCSR_ENDINTR) {
-		if (camera_status & overrun) {
+		/*
+		 * It's normal if the last frame creates an overrun, as there
+		 * are no more DMA descriptors to fetch from QCI fifos
+		 */
+		if (camera_status & overrun &&
+		    !list_is_last(pcdev->capture.next, &pcdev->capture)) {
 			dev_dbg(pcdev->dev, "FIFO overrun! CISR: %x\n",
 				camera_status);
 			pxa_camera_stop_capture(pcdev);