diff options
| -rw-r--r-- | drivers/staging/media/imx/imx7-media-csi.c | 76 |
1 files changed, 76 insertions, 0 deletions
diff --git a/drivers/staging/media/imx/imx7-media-csi.c b/drivers/staging/media/imx/imx7-media-csi.c index cb7d8381f6f2..e643a9f38cc8 100644 --- a/drivers/staging/media/imx/imx7-media-csi.c +++ b/drivers/staging/media/imx/imx7-media-csi.c @@ -1295,12 +1295,88 @@ static int imx7_csi_video_buf_prepare(struct vb2_buffer *vb) return 0; } +static bool imx7_csi_fast_track_buffer(struct imx7_csi *csi, + struct imx7_csi_vb2_buffer *buf) +{ + unsigned long flags; + dma_addr_t phys; + int buf_num; + u32 isr; + + if (!csi->is_streaming) + return false; + + phys = vb2_dma_contig_plane_dma_addr(&buf->vbuf.vb2_buf, 0); + + /* + * buf_num holds the framebuffer ID of the most recently (*not* the + * next anticipated) triggered interrupt. Without loss of generality, + * if buf_num is 0, the hardware is capturing to FB2. If FB1 has been + * programmed with a dummy buffer (as indicated by active_vb2_buf[0] + * being NULL), then we can fast-track the new buffer by programming + * its address in FB1 before the hardware completes FB2, instead of + * adding it to the buffer queue and incurring a delay of one + * additional frame. + * + * The irqlock prevents races with the interrupt handler that updates + * buf_num when it programs the next buffer, but we can still race with + * the hardware if we program the buffer in FB1 just after the hardware + * completes FB2 and switches to FB1 and before buf_num can be updated + * by the interrupt handler for FB2. The fast-tracked buffer would + * then be ignored by the hardware while the driver would think it has + * successfully been processed. + * + * To avoid this problem, if we can't avoid the race, we can detect + * that we have lost it by checking, after programming the buffer in + * FB1, if the interrupt flag indicating completion of FB2 has been + * raised. If that is not the case, fast-tracking succeeded, and we can + * update active_vb2_buf[0]. Otherwise, we may or may not have lost the + * race (as the interrupt flag may have been raised just after + * programming FB1 and before we read the interrupt status register), + * and we need to assume the worst case of a race loss and queue the + * buffer through the slow path. + */ + + spin_lock_irqsave(&csi->irqlock, flags); + + buf_num = csi->buf_num; + if (csi->active_vb2_buf[buf_num]) { + spin_unlock_irqrestore(&csi->irqlock, flags); + return false; + } + + imx7_csi_update_buf(csi, phys, buf_num); + + isr = imx7_csi_reg_read(csi, CSI_CSISR); + if (isr & (buf_num ? BIT_DMA_TSF_DONE_FB1 : BIT_DMA_TSF_DONE_FB2)) { + /* + * The interrupt for the /other/ FB just came (the isr hasn't + * run yet though, because we have the lock here); we can't be + * sure we've programmed buf_num FB in time, so queue the buffer + * to the buffer queue normally. No need to undo writing the FB + * register, since we won't return it as active_vb2_buf is NULL, + * so it's okay to potentially write it to both FB1 and FB2; + * only the one where it was queued normally will be returned. + */ + spin_unlock_irqrestore(&csi->irqlock, flags); + return false; + } + + csi->active_vb2_buf[buf_num] = buf; + + spin_unlock_irqrestore(&csi->irqlock, flags); + return true; +} + static void imx7_csi_video_buf_queue(struct vb2_buffer *vb) { struct imx7_csi *csi = vb2_get_drv_priv(vb->vb2_queue); struct imx7_csi_vb2_buffer *buf = to_imx7_csi_vb2_buffer(vb); unsigned long flags; + if (imx7_csi_fast_track_buffer(csi, buf)) + return; + spin_lock_irqsave(&csi->q_lock, flags); list_add_tail(&buf->list, &csi->ready_q); |