V4L/DVB (11321): pxa_camera: Redesign DMA handling
The DMA transfers in pxa_camera showed some weaknesses in
multiple queued buffers context :
- poll/select problem
The bug shows up with capture_example tool from v4l2 hg
tree. The process just "stalls" on a "select timeout".
- multiple buffers DMA starting
When multiple buffers were queued, the DMA channels were
always started right away. This is not optimal, as a
special case appears when the first EOF was not yet
reached, and the DMA channels were prematurely started.
- Maintainability
DMA code was a bit obfuscated. Rationalize the code to be
easily maintainable by anyone.
- DMA hot chaining
DMA is not stopped anymore to queue a buffer, the buffer
is queued with DMA running. As a tribute, a corner case
exists where chaining happens while DMA finishes the
chain, and the capture is restarted to deal with the
missed link buffer.
This patch attemps to address these issues / improvements.
create mode 100644 Documentation/video4linux/pxa_camera.txt
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>
diff --git a/drivers/media/video/pxa_camera.c b/drivers/media/video/pxa_camera.c
index 07f792b..a2f98ec 100644
--- a/drivers/media/video/pxa_camera.c
+++ b/drivers/media/video/pxa_camera.c
@@ -369,6 +369,10 @@
pxa_dma->sg_cpu[i].dtadr = sg_dma_address(sg) + offset;
pxa_dma->sg_cpu[i].dcmd =
DCMD_FLOWSRC | DCMD_BURST8 | DCMD_INCTRGADDR | xfer_len;
+#ifdef DEBUG
+ if (!i)
+ pxa_dma->sg_cpu[i].dcmd |= DCMD_STARTIRQEN;
+#endif
pxa_dma->sg_cpu[i].ddadr =
pxa_dma->sg_dma + (i + 1) * sizeof(struct pxa_dma_desc);
@@ -381,8 +385,8 @@
break;
}
- pxa_dma->sg_cpu[sglen - 1].ddadr = DDADR_STOP;
- pxa_dma->sg_cpu[sglen - 1].dcmd |= DCMD_ENDIRQEN;
+ pxa_dma->sg_cpu[sglen].ddadr = DDADR_STOP;
+ pxa_dma->sg_cpu[sglen].dcmd = DCMD_FLOWSRC | DCMD_BURST8 | DCMD_ENDIRQEN;
/*
* Handle 1 special case :
@@ -402,6 +406,20 @@
return 0;
}
+static void pxa_videobuf_set_actdma(struct pxa_camera_dev *pcdev,
+ struct pxa_buffer *buf)
+{
+ buf->active_dma = DMA_Y;
+ if (pcdev->channels == 3)
+ buf->active_dma |= DMA_U | DMA_V;
+}
+
+/*
+ * Please check the DMA prepared buffer structure in :
+ * Documentation/video4linux/pxa_camera.txt
+ * Please check also in pxa_camera_check_link_miss() to understand why DMA chain
+ * modification while DMA chain is running will work anyway.
+ */
static int pxa_videobuf_prepare(struct videobuf_queue *vq,
struct videobuf_buffer *vb, enum v4l2_field field)
{
@@ -499,9 +517,7 @@
}
buf->inwork = 0;
- buf->active_dma = DMA_Y;
- if (pcdev->channels == 3)
- buf->active_dma |= DMA_U | DMA_V;
+ pxa_videobuf_set_actdma(pcdev, buf);
return 0;
@@ -518,6 +534,99 @@
return ret;
}
+/**
+ * pxa_dma_start_channels - start DMA channel for active buffer
+ * @pcdev: pxa camera device
+ *
+ * Initialize DMA channels to the beginning of the active video buffer, and
+ * start these channels.
+ */
+static void pxa_dma_start_channels(struct pxa_camera_dev *pcdev)
+{
+ int i;
+ struct pxa_buffer *active;
+
+ active = pcdev->active;
+
+ for (i = 0; i < pcdev->channels; i++) {
+ dev_dbg(pcdev->dev, "%s (channel=%d) ddadr=%08x\n", __func__,
+ i, active->dmas[i].sg_dma);
+ DDADR(pcdev->dma_chans[i]) = active->dmas[i].sg_dma;
+ DCSR(pcdev->dma_chans[i]) = DCSR_RUN;
+ }
+}
+
+static void pxa_dma_stop_channels(struct pxa_camera_dev *pcdev)
+{
+ int i;
+
+ for (i = 0; i < pcdev->channels; i++) {
+ dev_dbg(pcdev->dev, "%s (channel=%d)\n", __func__, i);
+ DCSR(pcdev->dma_chans[i]) = 0;
+ }
+}
+
+static void pxa_dma_update_sg_tail(struct pxa_camera_dev *pcdev,
+ struct pxa_buffer *buf)
+{
+ int i;
+
+ for (i = 0; i < pcdev->channels; i++)
+ pcdev->sg_tail[i] = buf->dmas[i].sg_cpu + buf->dmas[i].sglen;
+}
+
+static void pxa_dma_add_tail_buf(struct pxa_camera_dev *pcdev,
+ struct pxa_buffer *buf)
+{
+ int i;
+ struct pxa_dma_desc *buf_last_desc;
+
+ for (i = 0; i < pcdev->channels; i++) {
+ buf_last_desc = buf->dmas[i].sg_cpu + buf->dmas[i].sglen;
+ buf_last_desc->ddadr = DDADR_STOP;
+
+ if (!pcdev->sg_tail[i])
+ continue;
+ pcdev->sg_tail[i]->ddadr = buf->dmas[i].sg_dma;
+ }
+
+ pxa_dma_update_sg_tail(pcdev, buf);
+}
+
+/**
+ * pxa_camera_start_capture - start video capturing
+ * @pcdev: camera device
+ *
+ * Launch capturing. DMA channels should not be active yet. They should get
+ * activated at the end of frame interrupt, to capture only whole frames, and
+ * never begin the capture of a partial frame.
+ */
+static void pxa_camera_start_capture(struct pxa_camera_dev *pcdev)
+{
+ unsigned long cicr0, cifr;
+
+ dev_dbg(pcdev->dev, "%s\n", __func__);
+ /* Reset the FIFOs */
+ cifr = __raw_readl(pcdev->base + CIFR) | CIFR_RESET_F;
+ __raw_writel(cifr, pcdev->base + CIFR);
+ /* Enable End-Of-Frame Interrupt */
+ cicr0 = __raw_readl(pcdev->base + CICR0) | CICR0_ENB;
+ cicr0 &= ~CICR0_EOFM;
+ __raw_writel(cicr0, pcdev->base + CICR0);
+}
+
+static void pxa_camera_stop_capture(struct pxa_camera_dev *pcdev)
+{
+ unsigned long cicr0;
+
+ pxa_dma_stop_channels(pcdev);
+
+ cicr0 = __raw_readl(pcdev->base + CICR0) & ~CICR0_ENB;
+ __raw_writel(cicr0, pcdev->base + CICR0);
+
+ dev_dbg(pcdev->dev, "%s\n", __func__);
+}
+
static void pxa_videobuf_queue(struct videobuf_queue *vq,
struct videobuf_buffer *vb)
{
@@ -525,81 +634,20 @@
struct soc_camera_host *ici = to_soc_camera_host(icd->dev.parent);
struct pxa_camera_dev *pcdev = ici->priv;
struct pxa_buffer *buf = container_of(vb, struct pxa_buffer, vb);
- struct pxa_buffer *active;
unsigned long flags;
- int i;
- dev_dbg(&icd->dev, "%s (vb=0x%p) 0x%08lx %d\n", __func__,
- vb, vb->baddr, vb->bsize);
+ dev_dbg(&icd->dev, "%s (vb=0x%p) 0x%08lx %d active=%p\n", __func__,
+ vb, vb->baddr, vb->bsize, pcdev->active);
+
spin_lock_irqsave(&pcdev->lock, flags);
list_add_tail(&vb->queue, &pcdev->capture);
vb->state = VIDEOBUF_ACTIVE;
- active = pcdev->active;
+ pxa_dma_add_tail_buf(pcdev, buf);
- if (!active) {
- unsigned long cifr, cicr0;
-
- cifr = __raw_readl(pcdev->base + CIFR) | CIFR_RESET_F;
- __raw_writel(cifr, pcdev->base + CIFR);
-
- for (i = 0; i < pcdev->channels; i++) {
- DDADR(pcdev->dma_chans[i]) = buf->dmas[i].sg_dma;
- DCSR(pcdev->dma_chans[i]) = DCSR_RUN;
- pcdev->sg_tail[i] = buf->dmas[i].sg_cpu + buf->dmas[i].sglen - 1;
- }
-
- pcdev->active = buf;
-
- cicr0 = __raw_readl(pcdev->base + CICR0) | CICR0_ENB;
- __raw_writel(cicr0, pcdev->base + CICR0);
- } else {
- struct pxa_cam_dma *buf_dma;
- struct pxa_cam_dma *act_dma;
- int nents;
-
- for (i = 0; i < pcdev->channels; i++) {
- buf_dma = &buf->dmas[i];
- act_dma = &active->dmas[i];
- nents = buf_dma->sglen;
-
- /* Stop DMA engine */
- DCSR(pcdev->dma_chans[i]) = 0;
-
- /* Add the descriptors we just initialized to
- the currently running chain */
- pcdev->sg_tail[i]->ddadr = buf_dma->sg_dma;
- pcdev->sg_tail[i] = buf_dma->sg_cpu + buf_dma->sglen - 1;
-
- /* Setup a dummy descriptor with the DMA engines current
- * state
- */
- buf_dma->sg_cpu[nents].dsadr =
- pcdev->res->start + 0x28 + i*8; /* CIBRx */
- buf_dma->sg_cpu[nents].dtadr =
- DTADR(pcdev->dma_chans[i]);
- buf_dma->sg_cpu[nents].dcmd =
- DCMD(pcdev->dma_chans[i]);
-
- if (DDADR(pcdev->dma_chans[i]) == DDADR_STOP) {
- /* The DMA engine is on the last
- descriptor, set the next descriptors
- address to the descriptors we just
- initialized */
- buf_dma->sg_cpu[nents].ddadr = buf_dma->sg_dma;
- } else {
- buf_dma->sg_cpu[nents].ddadr =
- DDADR(pcdev->dma_chans[i]);
- }
-
- /* The next descriptor is the dummy descriptor */
- DDADR(pcdev->dma_chans[i]) = buf_dma->sg_dma + nents *
- sizeof(struct pxa_dma_desc);
-
- DCSR(pcdev->dma_chans[i]) = DCSR_RUN;
- }
- }
+ if (!pcdev->active)
+ pxa_camera_start_capture(pcdev);
spin_unlock_irqrestore(&pcdev->lock, flags);
}
@@ -637,7 +685,7 @@
struct videobuf_buffer *vb,
struct pxa_buffer *buf)
{
- unsigned long cicr0;
+ int i;
/* _init is used to debug races, see comment in pxa_camera_reqbufs() */
list_del_init(&vb->queue);
@@ -645,15 +693,13 @@
do_gettimeofday(&vb->ts);
vb->field_count++;
wake_up(&vb->done);
+ dev_dbg(pcdev->dev, "%s dequeud buffer (vb=0x%p)\n", __func__, vb);
if (list_empty(&pcdev->capture)) {
+ pxa_camera_stop_capture(pcdev);
pcdev->active = NULL;
- DCSR(pcdev->dma_chans[0]) = 0;
- DCSR(pcdev->dma_chans[1]) = 0;
- DCSR(pcdev->dma_chans[2]) = 0;
-
- cicr0 = __raw_readl(pcdev->base + CICR0) & ~CICR0_ENB;
- __raw_writel(cicr0, pcdev->base + CICR0);
+ for (i = 0; i < pcdev->channels; i++)
+ pcdev->sg_tail[i] = NULL;
return;
}
@@ -661,6 +707,35 @@
struct pxa_buffer, vb.queue);
}
+/**
+ * pxa_camera_check_link_miss - check missed DMA linking
+ * @pcdev: camera device
+ *
+ * The DMA chaining is done with DMA running. This means a tiny temporal window
+ * remains, where a buffer is queued on the chain, while the chain is already
+ * stopped. This means the tailed buffer would never be transfered by DMA.
+ * This function restarts the capture for this corner case, where :
+ * - DADR() == DADDR_STOP
+ * - a videobuffer is queued on the pcdev->capture list
+ *
+ * Please check the "DMA hot chaining timeslice issue" in
+ * Documentation/video4linux/pxa_camera.txt
+ *
+ * Context: should only be called within the dma irq handler
+ */
+static void pxa_camera_check_link_miss(struct pxa_camera_dev *pcdev)
+{
+ int i, is_dma_stopped = 1;
+
+ for (i = 0; i < pcdev->channels; i++)
+ if (DDADR(pcdev->dma_chans[i]) != DDADR_STOP)
+ is_dma_stopped = 0;
+ dev_dbg(pcdev->dev, "%s : top queued buffer=%p, dma_stopped=%d\n",
+ __func__, pcdev->active, is_dma_stopped);
+ if (pcdev->active && is_dma_stopped)
+ pxa_camera_start_capture(pcdev);
+}
+
static void pxa_camera_dma_irq(int channel, struct pxa_camera_dev *pcdev,
enum pxa_camera_active_dma act_dma)
{
@@ -668,19 +743,23 @@
unsigned long flags;
u32 status, camera_status, overrun;
struct videobuf_buffer *vb;
- unsigned long cifr, cicr0;
spin_lock_irqsave(&pcdev->lock, flags);
status = DCSR(channel);
- DCSR(channel) = status | DCSR_ENDINTR;
+ DCSR(channel) = status;
+
+ camera_status = __raw_readl(pcdev->base + CISR);
+ overrun = CISR_IFO_0;
+ if (pcdev->channels == 3)
+ overrun |= CISR_IFO_1 | CISR_IFO_2;
if (status & DCSR_BUSERR) {
dev_err(pcdev->dev, "DMA Bus Error IRQ!\n");
goto out;
}
- if (!(status & DCSR_ENDINTR)) {
+ if (!(status & (DCSR_ENDINTR | DCSR_STARTINTR))) {
dev_err(pcdev->dev, "Unknown DMA IRQ source, "
"status: 0x%08x\n", status);
goto out;
@@ -691,38 +770,28 @@
goto out;
}
- camera_status = __raw_readl(pcdev->base + CISR);
- overrun = CISR_IFO_0;
- if (pcdev->channels == 3)
- overrun |= CISR_IFO_1 | CISR_IFO_2;
- if (camera_status & overrun) {
- dev_dbg(pcdev->dev, "FIFO overrun! CISR: %x\n", camera_status);
- /* Stop the Capture Interface */
- cicr0 = __raw_readl(pcdev->base + CICR0) & ~CICR0_ENB;
- __raw_writel(cicr0, pcdev->base + CICR0);
-
- /* Stop DMA */
- DCSR(channel) = 0;
- /* Reset the FIFOs */
- cifr = __raw_readl(pcdev->base + CIFR) | CIFR_RESET_F;
- __raw_writel(cifr, pcdev->base + CIFR);
- /* Enable End-Of-Frame Interrupt */
- cicr0 &= ~CICR0_EOFM;
- __raw_writel(cicr0, pcdev->base + CICR0);
- /* Restart the Capture Interface */
- __raw_writel(cicr0 | CICR0_ENB, pcdev->base + CICR0);
- goto out;
- }
-
vb = &pcdev->active->vb;
buf = container_of(vb, struct pxa_buffer, vb);
WARN_ON(buf->inwork || list_empty(&vb->queue));
- dev_dbg(pcdev->dev, "%s (vb=0x%p) 0x%08lx %d\n", __func__,
- vb, vb->baddr, vb->bsize);
- buf->active_dma &= ~act_dma;
- if (!buf->active_dma)
- pxa_camera_wakeup(pcdev, vb, buf);
+ dev_dbg(pcdev->dev, "%s channel=%d %s%s(vb=0x%p) dma.desc=%x\n",
+ __func__, channel, status & DCSR_STARTINTR ? "SOF " : "",
+ status & DCSR_ENDINTR ? "EOF " : "", vb, DDADR(channel));
+
+ if (status & DCSR_ENDINTR) {
+ if (camera_status & overrun) {
+ dev_dbg(pcdev->dev, "FIFO overrun! CISR: %x\n",
+ camera_status);
+ pxa_camera_stop_capture(pcdev);
+ pxa_camera_start_capture(pcdev);
+ goto out;
+ }
+ buf->active_dma &= ~act_dma;
+ if (!buf->active_dma) {
+ pxa_camera_wakeup(pcdev, vb, buf);
+ pxa_camera_check_link_miss(pcdev);
+ }
+ }
out:
spin_unlock_irqrestore(&pcdev->lock, flags);
@@ -851,6 +920,8 @@
{
struct pxa_camera_dev *pcdev = data;
unsigned long status, cicr0;
+ struct pxa_buffer *buf;
+ struct videobuf_buffer *vb;
status = __raw_readl(pcdev->base + CISR);
dev_dbg(pcdev->dev, "Camera interrupt status 0x%lx\n", status);
@@ -861,12 +932,14 @@
__raw_writel(status, pcdev->base + CISR);
if (status & CISR_EOF) {
- int i;
- for (i = 0; i < pcdev->channels; i++) {
- DDADR(pcdev->dma_chans[i]) =
- pcdev->active->dmas[i].sg_dma;
- DCSR(pcdev->dma_chans[i]) = DCSR_RUN;
- }
+ pcdev->active = list_first_entry(&pcdev->capture,
+ struct pxa_buffer, vb.queue);
+ vb = &pcdev->active->vb;
+ buf = container_of(vb, struct pxa_buffer, vb);
+ pxa_videobuf_set_actdma(pcdev, buf);
+
+ pxa_dma_start_channels(pcdev);
+
cicr0 = __raw_readl(pcdev->base + CICR0) | CICR0_EOFM;
__raw_writel(cicr0, pcdev->base + CICR0);
}
@@ -1449,18 +1522,8 @@
ret = pcdev->icd->ops->resume(pcdev->icd);
/* Restart frame capture if active buffer exists */
- if (!ret && pcdev->active) {
- unsigned long cifr, cicr0;
-
- /* Reset the FIFOs */
- cifr = __raw_readl(pcdev->base + CIFR) | CIFR_RESET_F;
- __raw_writel(cifr, pcdev->base + CIFR);
-
- cicr0 = __raw_readl(pcdev->base + CICR0);
- cicr0 &= ~CICR0_EOFM; /* Enable End-Of-Frame Interrupt */
- cicr0 |= CICR0_ENB; /* Restart the Capture Interface */
- __raw_writel(cicr0, pcdev->base + CICR0);
- }
+ if (!ret && pcdev->active)
+ pxa_camera_start_capture(pcdev);
return ret;
}