On Tue, 10 Mar 2009, Robert Jarzmik wrote:
> The DMA transfers in pxa_camera showed some weaknesses in
> multiple queued buffers context :
> - poll/select problem
> The order between list pcdev->capture and DMA chain was
> not the same. This creates a discrepancy between video
> buffers marked as "done" by the IRQ handler, and the
> really finished video buffer.
Double-check. I still do not see how the order can be swapped. But don't
worry, this doesn't diminish the value of your work, I'm just trying to be
fair to the existing driver:-)
>
> The bug shows up with capture_example tool from v4l2 hg
> tree. The process just "stalls" on a "select timeout".
>
> The key problem is in pxa_videobuf_queue(), where the
> queued buffer is chained before the active buffer, while
> it should have been the active buffer first, and queued
> buffer tailed after.
>
> - 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.
>
> This patch attemps to address these issues.
>
> Signed-off-by: Robert Jarzmik <robert.jarz...@free.fr>
> ---
> drivers/media/video/pxa_camera.c | 329 +++++++++++++++++++++++--------------
> 1 files changed, 204 insertions(+), 125 deletions(-)
>
> diff --git a/drivers/media/video/pxa_camera.c
> b/drivers/media/video/pxa_camera.c
> index aca5374..6ec8135 100644
> --- a/drivers/media/video/pxa_camera.c
> +++ b/drivers/media/video/pxa_camera.c
> @@ -324,7 +324,7 @@ static int calculate_dma_sglen(struct scatterlist
> *sglist, int sglen,
> * Prepares the pxa dma descriptors to transfer one camera channel.
> * Beware sg_first and sg_first_ofs are both input and output parameters.
> *
> - * Returns 0
> + * Returns 0 or -ENOMEM si no coherent memory is available
s/si/if/ s'il vous plait:-)
> */
> static int pxa_init_dma_channel(struct pxa_camera_dev *pcdev,
> struct pxa_buffer *buf,
> @@ -369,6 +369,10 @@ static int pxa_init_dma_channel(struct pxa_camera_dev
> *pcdev,
> 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);
>
> @@ -402,6 +406,47 @@ static int pxa_init_dma_channel(struct pxa_camera_dev
> *pcdev,
> return 0;
> }
>
> +/*
> + * A DMA prepared buffer will have this structure :
> + * +------------+-----+---------------+-----------------+
> + * | desc-sg[0] | ... | desc-sg[last] | finisher/linker |
> + * +------------+-----+---------------+-----------------+
> + *
> + * This structure is pointed by dma->sg_cpu.
> + * The descriptors are used as follows :
> + * - desc-sg[i]: i-th descriptor, transfering the i-th sg
> + * element to the video buffer scatter gather
> + * - finisher: has ddadr=DADDR_STOP, dcmd=ENDIRQEN
> + * - linker: has ddadr= desc-sg[0] of next video buffer, dcmd=0
> + *
> + * For the next schema, let's assume d0=desc-sg[0] .. dN=desc-sg[N],
> + * "f" stands for finisher and "l" for linker.
> + * A typical running chain is :
> + *
> + * Videobuffer 1 Videobuffer 2
> + * +---------+----+---+ +----+----+----+---+
> + * | d0 | .. | dN | l | | d0 | .. | dN | f |
> + * +---------+----+-|-+ ^----+----+----+---+
> + * | |
> + * +----+
> + *
> + * After the chaining is finished, the chain looks like :
> + *
> + * Videobuffer 1 Videobuffer 2 Videobuffer 3
> + * +---------+----+---+ +----+----+----+---+ +----+----+----+---+
> + * | d0 | .. | dN | l | | d0 | .. | dN | l | | d0 | .. | dN | f |
> + * +---------+----+-|-+ ^----+----+----+-|-+ ^----+----+----+---+
> + * | | | |
> + * +----+ +----+
> + * new_link
> + *
> + * Now, the chaining done in pxa_videobuf_queue, creating "new_link" can
> happen
> + * while the DMA chain as already jumped to Videobuffer 2 "finisher". In this
> + * case, the DMA chain is stopped, and the DMA irq handler is pending.
> + * Then, the DMA irq completion handler will check if the DMA is finished
> and a
> + * buffer is still on the pcdev->capture list. If that's the case, the
> capture
> + * will be restarted.
> + */
Nice, how about putting this in Documentation/video4linux/pxa_camera.txt
and a reference to it in the comment?
> static int pxa_videobuf_prepare(struct videobuf_queue *vq,
> struct videobuf_buffer *vb, enum v4l2_field field)
> {
> @@ -517,6 +562,96 @@ out:
> 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;
> + pcdev->sg_tail[i]->ddadr = DDADR_STOP;
This function is now called "live" with running DMA, and you first append
the chain, and only then terminate it... It should be ok because it is
done with switched off IRQs, and DMA must be still at tail - 1 to
automatically continue onto the appended chain, so, you should have enough
time in 100% of cases, still it would look better to first terminate the
chain and then append it.
> + }
> +}
> +
> +static void pxa_dma_add_tail_buf(struct pxa_camera_dev *pcdev,
> + struct pxa_buffer *buf)
> +{
> + int i;
> +
> + for (i = 0; i < pcdev->channels; i++) {
> + 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__);
<quote>
I originally had a "reset the FIFOs" comment here, wouldn't hurt to add it
now too.
</quote>
> + cifr = __raw_readl(pcdev->base + CIFR) | CIFR_RESET_F;
> + __raw_writel(cifr, pcdev->base + CIFR);
> +
> + 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)
> {
> @@ -524,81 +659,19 @@ static void pxa_videobuf_queue(struct videobuf_queue
> *vq,
> 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);
> - spin_lock_irqsave(&pcdev->lock, flags);
> + 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);
I can understand adding an empty line between dev_dbg() and
spin_lock_irqsave(), but I do not understand why you removed one between
spin_lock_irqsave() and list_add_tail().
>
> vb->state = VIDEOBUF_ACTIVE;
> - active = pcdev->active;
> -
> - 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;
> - }
> + pxa_dma_add_tail_buf(pcdev, buf);
>
> - 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);
> }
> @@ -636,7 +709,7 @@ static void pxa_camera_wakeup(struct pxa_camera_dev
> *pcdev,
> 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);
> @@ -644,15 +717,13 @@ static void pxa_camera_wakeup(struct pxa_camera_dev
> *pcdev,
> 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;
> }
>
> @@ -660,6 +731,32 @@ static void pxa_camera_wakeup(struct pxa_camera_dev
> *pcdev,
> 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
> + *
> + * 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)
> {
> @@ -667,19 +764,23 @@ static void pxa_camera_dma_irq(int channel, struct
> pxa_camera_dev *pcdev,
> 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;
> @@ -690,38 +791,27 @@ static void pxa_camera_dma_irq(int channel, struct
> pxa_camera_dev *pcdev,
> 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);
> @@ -860,12 +950,11 @@ static irqreturn_t pxa_camera_irq(int irq, void *data)
> __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);
> +
> + pxa_dma_start_channels(pcdev);
> +
> cicr0 = __raw_readl(pcdev->base + CICR0) | CICR0_EOFM;
> __raw_writel(cicr0, pcdev->base + CICR0);
> }
> @@ -1417,18 +1506,8 @@ static int pxa_camera_resume(struct soc_camera_device
> *icd)
> 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;
> }
> --
> 1.5.6.5
>
Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
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