The way discard buffer was previously handled lead
to possible races that made a buffer that was not
yet ready to be overwritten by new video data. This
is easily detected at 25fps just adding "#define DEBUG"
to enable the "memset" check and seeing how the image
is corrupted.

A new "discard" queue and two discard buffers have
been added to make them flow trough the pipeline
of queues and thus provide suitable event ordering.

Signed-off-by: Javier Martin <javier.mar...@vista-silicon.com>
---
 Changes since v1:
 - Don't allocate discard buffer on every set_fmt.

---
 drivers/media/video/mx2_camera.c |  261 +++++++++++++++++++++-----------------
 1 files changed, 144 insertions(+), 117 deletions(-)

diff --git a/drivers/media/video/mx2_camera.c b/drivers/media/video/mx2_camera.c
index 045c018..71054ab 100644
--- a/drivers/media/video/mx2_camera.c
+++ b/drivers/media/video/mx2_camera.c
@@ -237,7 +237,8 @@ struct mx2_buffer {
        struct list_head                queue;
        enum mx2_buffer_state           state;
 
-       int bufnum;
+       int                             bufnum;
+       bool                            discard;
 };
 
 struct mx2_camera_dev {
@@ -256,6 +257,7 @@ struct mx2_camera_dev {
 
        struct list_head        capture;
        struct list_head        active_bufs;
+       struct list_head        discard;
 
        spinlock_t              lock;
 
@@ -268,6 +270,7 @@ struct mx2_camera_dev {
 
        u32                     csicr1;
 
+       struct mx2_buffer       buf_discard[2];
        void                    *discard_buffer;
        dma_addr_t              discard_buffer_dma;
        size_t                  discard_size;
@@ -329,6 +332,30 @@ static struct mx2_fmt_cfg *mx27_emma_prp_get_format(
        return &mx27_emma_prp_table[0];
 };
 
+static void mx27_update_emma_buf(struct mx2_camera_dev *pcdev,
+                                unsigned long phys, int bufnum)
+{
+       struct mx2_fmt_cfg *prp = pcdev->emma_prp;
+
+       if (prp->cfg.channel == 1) {
+               writel(phys, pcdev->base_emma +
+                               PRP_DEST_RGB1_PTR + 4 * bufnum);
+       } else {
+               writel(phys, pcdev->base_emma +
+                       PRP_DEST_Y_PTR - 0x14 * bufnum);
+               if (prp->out_fmt == V4L2_PIX_FMT_YUV420) {
+                       u32 imgsize = pcdev->icd->user_height *
+                                       pcdev->icd->user_width;
+
+                       writel(phys + imgsize,
+                       pcdev->base_emma + PRP_DEST_CB_PTR -
+                       0x14 * bufnum);
+                       writel(phys + ((5 * imgsize) / 4), pcdev->base_emma +
+                       PRP_DEST_CR_PTR - 0x14 * bufnum);
+               }
+       }
+}
+
 static void mx2_camera_deactivate(struct mx2_camera_dev *pcdev)
 {
        unsigned long flags;
@@ -377,7 +404,7 @@ static int mx2_camera_add_device(struct soc_camera_device 
*icd)
        writel(pcdev->csicr1, pcdev->base_csi + CSICR1);
 
        pcdev->icd = icd;
-       pcdev->frame_count = -1;
+       pcdev->frame_count = 0;
 
        dev_info(icd->parent, "Camera driver attached to camera %d\n",
                 icd->devnum);
@@ -631,7 +658,7 @@ static void mx2_videobuf_release(struct vb2_buffer *vb)
 
        spin_lock_irqsave(&pcdev->lock, flags);
        if (mx27_camera_emma(pcdev)) {
-               list_del_init(&buf->queue);
+               INIT_LIST_HEAD(&buf->queue);
        } else if (cpu_is_mx25() && buf->state == MX2_STATE_ACTIVE) {
                if (pcdev->fb1_active == buf) {
                        pcdev->csicr1 &= ~CSICR1_FB1_DMA_INTEN;
@@ -647,6 +674,34 @@ static void mx2_videobuf_release(struct vb2_buffer *vb)
        spin_unlock_irqrestore(&pcdev->lock, flags);
 }
 
+static void mx27_camera_emma_buf_init(struct soc_camera_device *icd,
+               int bytesperline)
+{
+       struct soc_camera_host *ici =
+               to_soc_camera_host(icd->parent);
+       struct mx2_camera_dev *pcdev = ici->priv;
+       struct mx2_fmt_cfg *prp = pcdev->emma_prp;
+
+       writel((icd->user_width << 16) | icd->user_height,
+              pcdev->base_emma + PRP_SRC_FRAME_SIZE);
+       writel(prp->cfg.src_pixel,
+              pcdev->base_emma + PRP_SRC_PIXEL_FORMAT_CNTL);
+       if (prp->cfg.channel == 1) {
+               writel((icd->user_width << 16) | icd->user_height,
+                       pcdev->base_emma + PRP_CH1_OUT_IMAGE_SIZE);
+               writel(bytesperline,
+                       pcdev->base_emma + PRP_DEST_CH1_LINE_STRIDE);
+               writel(prp->cfg.ch1_pixel,
+                       pcdev->base_emma + PRP_CH1_PIXEL_FORMAT_CNTL);
+       } else { /* channel 2 */
+               writel((icd->user_width << 16) | icd->user_height,
+                       pcdev->base_emma + PRP_CH2_OUT_IMAGE_SIZE);
+       }
+
+       /* Enable interrupts */
+       writel(prp->cfg.irq_flags, pcdev->base_emma + PRP_INTR_CNTL);
+}
+
 static int mx2_start_streaming(struct vb2_queue *q, unsigned int count)
 {
        struct soc_camera_device *icd = soc_camera_from_vb2q(q);
@@ -654,7 +709,11 @@ static int mx2_start_streaming(struct vb2_queue *q, 
unsigned int count)
                to_soc_camera_host(icd->parent);
        struct mx2_camera_dev *pcdev = ici->priv;
        struct mx2_fmt_cfg *prp = pcdev->emma_prp;
+       struct vb2_buffer *vb;
+       struct mx2_buffer *buf;
        unsigned long flags;
+       unsigned long phys;
+       int bytesperline;
        int ret = 0;
 
        spin_lock_irqsave(&pcdev->lock, flags);
@@ -664,6 +723,63 @@ static int mx2_start_streaming(struct vb2_queue *q, 
unsigned int count)
                        goto err;
                }
 
+               buf = list_entry(pcdev->capture.next,
+                                struct mx2_buffer, queue);
+               buf->bufnum = 0;
+               vb = &buf->vb;
+               buf->state = MX2_STATE_ACTIVE;
+
+               phys = vb2_dma_contig_plane_dma_addr(vb, 0);
+               mx27_update_emma_buf(pcdev, phys, buf->bufnum);
+               list_move_tail(pcdev->capture.next, &pcdev->active_bufs);
+
+               buf = list_entry(pcdev->capture.next,
+                                struct mx2_buffer, queue);
+               buf->bufnum = 1;
+               vb = &buf->vb;
+               buf->state = MX2_STATE_ACTIVE;
+
+               phys = vb2_dma_contig_plane_dma_addr(vb, 0);
+               mx27_update_emma_buf(pcdev, phys, buf->bufnum);
+               list_move_tail(pcdev->capture.next, &pcdev->active_bufs);
+
+               if (pcdev->discard_buffer) {
+                       dma_free_coherent(ici->v4l2_dev.dev,
+                               pcdev->discard_size, pcdev->discard_buffer,
+                               pcdev->discard_buffer_dma);
+
+                       pcdev->buf_discard[0].discard = true;
+                       INIT_LIST_HEAD(&pcdev->buf_discard[0].queue);
+                       list_add_tail(&pcdev->buf_discard[0].queue,
+                                     &pcdev->discard);
+
+                       pcdev->buf_discard[1].discard = true;
+                       INIT_LIST_HEAD(&pcdev->buf_discard[1].queue);
+                       list_add_tail(&pcdev->buf_discard[1].queue,
+                                     &pcdev->discard);
+               }
+
+               bytesperline = soc_mbus_bytes_per_line(icd->user_width,
+                               icd->current_fmt->host_fmt);
+               if (bytesperline < 0)
+                       return bytesperline;
+
+               /*
+                * I didn't manage to properly enable/disable the prp
+                * on a per frame basis during running transfers,
+                * thus we allocate a buffer here and use it to
+                * discard frames when no buffer is available.
+                * Feel free to work on this ;)
+                */
+               pcdev->discard_size = icd->user_height * bytesperline;
+               pcdev->discard_buffer = dma_alloc_coherent(ici->v4l2_dev.dev,
+                               pcdev->discard_size, &pcdev->discard_buffer_dma,
+                               GFP_KERNEL);
+               if (!pcdev->discard_buffer)
+                       return -ENOMEM;
+
+               mx27_camera_emma_buf_init(icd, bytesperline);
+
                if (prp->cfg.channel == 1) {
                        writel(PRP_CNTL_CH1EN |
                                PRP_CNTL_CSIEN |
@@ -711,6 +827,9 @@ static int mx2_stop_streaming(struct vb2_queue *q)
                        writel(cntl & ~PRP_CNTL_CH2EN,
                               pcdev->base_emma + PRP_CNTL);
                }
+               INIT_LIST_HEAD(&pcdev->capture);
+               INIT_LIST_HEAD(&pcdev->active_bufs);
+               INIT_LIST_HEAD(&pcdev->discard);
        }
        spin_unlock_irqrestore(&pcdev->lock, flags);
 
@@ -766,63 +885,6 @@ static int mx27_camera_emma_prp_reset(struct 
mx2_camera_dev *pcdev)
        return -ETIMEDOUT;
 }
 
-static void mx27_camera_emma_buf_init(struct soc_camera_device *icd,
-               int bytesperline)
-{
-       struct soc_camera_host *ici =
-               to_soc_camera_host(icd->parent);
-       struct mx2_camera_dev *pcdev = ici->priv;
-       struct mx2_fmt_cfg *prp = pcdev->emma_prp;
-       u32 imgsize = pcdev->icd->user_height * pcdev->icd->user_width;
-
-       if (prp->cfg.channel == 1) {
-               writel(pcdev->discard_buffer_dma,
-                               pcdev->base_emma + PRP_DEST_RGB1_PTR);
-               writel(pcdev->discard_buffer_dma,
-                               pcdev->base_emma + PRP_DEST_RGB2_PTR);
-
-               writel((icd->user_width << 16) | icd->user_height,
-                       pcdev->base_emma + PRP_SRC_FRAME_SIZE);
-               writel((icd->user_width << 16) | icd->user_height,
-                       pcdev->base_emma + PRP_CH1_OUT_IMAGE_SIZE);
-               writel(bytesperline,
-                       pcdev->base_emma + PRP_DEST_CH1_LINE_STRIDE);
-               writel(prp->cfg.src_pixel,
-                       pcdev->base_emma + PRP_SRC_PIXEL_FORMAT_CNTL);
-               writel(prp->cfg.ch1_pixel,
-                       pcdev->base_emma + PRP_CH1_PIXEL_FORMAT_CNTL);
-       } else { /* channel 2 */
-               writel(pcdev->discard_buffer_dma,
-                       pcdev->base_emma + PRP_DEST_Y_PTR);
-               writel(pcdev->discard_buffer_dma,
-                       pcdev->base_emma + PRP_SOURCE_Y_PTR);
-
-               if (prp->cfg.out_fmt == PRP_CNTL_CH2_OUT_YUV420) {
-                       writel(pcdev->discard_buffer_dma + imgsize,
-                               pcdev->base_emma + PRP_DEST_CB_PTR);
-                       writel(pcdev->discard_buffer_dma + ((5 * imgsize) / 4),
-                               pcdev->base_emma + PRP_DEST_CR_PTR);
-                       writel(pcdev->discard_buffer_dma + imgsize,
-                               pcdev->base_emma + PRP_SOURCE_CB_PTR);
-                       writel(pcdev->discard_buffer_dma + ((5 * imgsize) / 4),
-                               pcdev->base_emma + PRP_SOURCE_CR_PTR);
-               }
-
-               writel((icd->user_width << 16) | icd->user_height,
-                       pcdev->base_emma + PRP_SRC_FRAME_SIZE);
-
-               writel((icd->user_width << 16) | icd->user_height,
-                       pcdev->base_emma + PRP_CH2_OUT_IMAGE_SIZE);
-
-               writel(prp->cfg.src_pixel,
-                       pcdev->base_emma + PRP_SRC_PIXEL_FORMAT_CNTL);
-
-       }
-
-       /* Enable interrupts */
-       writel(prp->cfg.irq_flags, pcdev->base_emma + PRP_INTR_CNTL);
-}
-
 static int mx2_camera_set_bus_param(struct soc_camera_device *icd,
                __u32 pixfmt)
 {
@@ -906,27 +968,6 @@ static int mx2_camera_set_bus_param(struct 
soc_camera_device *icd,
                ret = mx27_camera_emma_prp_reset(pcdev);
                if (ret)
                        return ret;
-
-               if (pcdev->discard_buffer)
-                       dma_free_coherent(ici->v4l2_dev.dev,
-                               pcdev->discard_size, pcdev->discard_buffer,
-                               pcdev->discard_buffer_dma);
-
-               /*
-                * I didn't manage to properly enable/disable the prp
-                * on a per frame basis during running transfers,
-                * thus we allocate a buffer here and use it to
-                * discard frames when no buffer is available.
-                * Feel free to work on this ;)
-                */
-               pcdev->discard_size = icd->user_height * bytesperline;
-               pcdev->discard_buffer = dma_alloc_coherent(ici->v4l2_dev.dev,
-                               pcdev->discard_size, &pcdev->discard_buffer_dma,
-                               GFP_KERNEL);
-               if (!pcdev->discard_buffer)
-                       return -ENOMEM;
-
-               mx27_camera_emma_buf_init(icd, bytesperline);
        } else if (cpu_is_mx25()) {
                writel((bytesperline * icd->user_height) >> 2,
                                pcdev->base_csi + CSIRXCNT);
@@ -1174,18 +1215,24 @@ static struct soc_camera_host_ops 
mx2_soc_camera_host_ops = {
 static void mx27_camera_frame_done_emma(struct mx2_camera_dev *pcdev,
                int bufnum)
 {
-       u32 imgsize = pcdev->icd->user_height * pcdev->icd->user_width;
-       struct mx2_fmt_cfg *prp = pcdev->emma_prp;
        struct mx2_buffer *buf;
        struct vb2_buffer *vb;
        unsigned long phys;
 
-       if (!list_empty(&pcdev->active_bufs)) {
-               buf = list_entry(pcdev->active_bufs.next,
-                       struct mx2_buffer, queue);
+       BUG_ON(list_empty(&pcdev->active_bufs));
+
+       buf = list_entry(pcdev->active_bufs.next,
+                        struct mx2_buffer, queue);
 
-               BUG_ON(buf->bufnum != bufnum);
+       BUG_ON(buf->bufnum != bufnum);
 
+       if (buf->discard) {
+               /*
+                * Discard buffer must not be returned to user space.
+                * Just return it to the discard queue.
+                */
+               list_move_tail(pcdev->active_bufs.next, &pcdev->discard);
+       } else {
                vb = &buf->vb;
 #ifdef DEBUG
                phys = vb2_dma_contig_plane_dma_addr(vb, 0);
@@ -1207,6 +1254,7 @@ static void mx27_camera_frame_done_emma(struct 
mx2_camera_dev *pcdev,
                        }
                }
 #endif
+
                dev_dbg(pcdev->dev, "%s (vb=0x%p) 0x%p %lu\n", __func__, vb,
                                vb2_plane_vaddr(vb, 0),
                                vb2_get_plane_payload(vb, 0));
@@ -1219,30 +1267,19 @@ static void mx27_camera_frame_done_emma(struct 
mx2_camera_dev *pcdev,
 
        pcdev->frame_count++;
 
-       if (list_empty(&pcdev->capture)) {
-               if (prp->cfg.channel == 1) {
-                       writel(pcdev->discard_buffer_dma, pcdev->base_emma +
-                                       PRP_DEST_RGB1_PTR + 4 * bufnum);
-               } else {
-                       writel(pcdev->discard_buffer_dma, pcdev->base_emma +
-                                               PRP_DEST_Y_PTR -
-                                               0x14 * bufnum);
-                       if (prp->out_fmt == V4L2_PIX_FMT_YUV420) {
-                               writel(pcdev->discard_buffer_dma + imgsize,
-                                      pcdev->base_emma + PRP_DEST_CB_PTR -
-                                      0x14 * bufnum);
-                               writel(pcdev->discard_buffer_dma +
-                                      ((5 * imgsize) / 4), pcdev->base_emma +
-                                      PRP_DEST_CR_PTR - 0x14 * bufnum);
-                       }
-               }
+       if (list_empty(&pcdev->capture) && !list_empty(&pcdev->discard)) {
+               buf = list_entry(pcdev->discard.next,
+                       struct mx2_buffer, queue);
+               buf->bufnum = bufnum;
+               list_move_tail(pcdev->discard.next, &pcdev->active_bufs);
+               mx27_update_emma_buf(pcdev, pcdev->discard_buffer_dma, bufnum);
                return;
        }
 
        buf = list_entry(pcdev->capture.next,
                        struct mx2_buffer, queue);
 
-       buf->bufnum = !bufnum;
+       buf->bufnum = bufnum;
 
        list_move_tail(pcdev->capture.next, &pcdev->active_bufs);
 
@@ -1250,18 +1287,7 @@ static void mx27_camera_frame_done_emma(struct 
mx2_camera_dev *pcdev,
        buf->state = MX2_STATE_ACTIVE;
 
        phys = vb2_dma_contig_plane_dma_addr(vb, 0);
-       if (prp->cfg.channel == 1) {
-               writel(phys, pcdev->base_emma + PRP_DEST_RGB1_PTR + 4 * bufnum);
-       } else {
-               writel(phys, pcdev->base_emma +
-                               PRP_DEST_Y_PTR - 0x14 * bufnum);
-               if (prp->cfg.out_fmt == PRP_CNTL_CH2_OUT_YUV420) {
-                       writel(phys + imgsize, pcdev->base_emma +
-                                       PRP_DEST_CB_PTR - 0x14 * bufnum);
-                       writel(phys + ((5 * imgsize) / 4), pcdev->base_emma +
-                                       PRP_DEST_CR_PTR - 0x14 * bufnum);
-               }
-       }
+       mx27_update_emma_buf(pcdev, phys, bufnum);
 }
 
 static irqreturn_t mx27_camera_emma_irq(int irq_emma, void *data)
@@ -1413,6 +1439,7 @@ static int __devinit mx2_camera_probe(struct 
platform_device *pdev)
 
        INIT_LIST_HEAD(&pcdev->capture);
        INIT_LIST_HEAD(&pcdev->active_bufs);
+       INIT_LIST_HEAD(&pcdev->discard);
        spin_lock_init(&pcdev->lock);
 
        /*
-- 
1.7.0.4

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