Re: [PATCH v5 14/14] media: ti: j721e-csi2rx: Wait for the last drain completion

dmaengine_terminate_sync() causes all activity for the DMA channel to be
stopped, and may discard data in the DMA FIFO which hasn't been fully
transferred. No callback functions will be called for any
incomplete transfers[1].

In multistream use case, calling dmaengine_terminate_sync() immediately
after issuing the last drain transaction will result in no callback
for the last drain cycle.

Implement complete callback for the last drain cycle to make sure that
the last drain has completed properly, this will ensure that stale data
is not left out in the HW FIFO.

[1] : https://docs.kernel.org/driver-api/dmaengine/client.html

Signed-off-by: Rishikesh Donadkar <redacted>
---
 drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c b/drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c
index 4ac6a76b9409..520ee05eb5b4 100644
--- a/drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c
+++ b/drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c

@@ -62,6 +62,7 @@
 #define TI_CSI2RX_MAX_PADS             (1 + TI_CSI2RX_MAX_SOURCE_PADS)
 
 #define DRAIN_BUFFER_SIZE              SZ_32K
+#define DRAIN_TIMEOUT_MS               50

 
 #define CSI2RX_BRIDGE_SOURCE_PAD       1
 

@@ -137,6 +138,7 @@ struct ti_csi2rx_dev {
                size_t                  len;
        } drain;
        bool                            vc_cached;
+       struct completion drain_complete;

 };
 
 static inline struct ti_csi2rx_dev *to_csi2rx_dev(struct v4l2_subdev *sd)

@@ -624,12 +626,14 @@ static void ti_csi2rx_setup_shim(struct ti_csi2rx_ctx *ctx)
 static void ti_csi2rx_drain_callback(void *param)
 {
        struct ti_csi2rx_ctx *ctx = param;
+       struct ti_csi2rx_dev *csi = ctx->csi;
        struct ti_csi2rx_dma *dma = &ctx->dma;
        unsigned long flags;
 
        spin_lock_irqsave(&dma->lock, flags);
 
        if (dma->state == TI_CSI2RX_DMA_STOPPED) {
+               complete(&csi->drain_complete);

                spin_unlock_irqrestore(&dma->lock, flags);
                return;
        }

@@ -774,6 +778,7 @@ static int ti_csi2rx_start_dma(struct ti_csi2rx_ctx *ctx,
 static void ti_csi2rx_stop_dma(struct ti_csi2rx_ctx *ctx)
 {
        struct ti_csi2rx_dma *dma = &ctx->dma;
+       struct ti_csi2rx_dev *csi = ctx->csi;
        enum ti_csi2rx_dma_state state;
        unsigned long flags;
        int ret;

@@ -783,6 +788,8 @@ static void ti_csi2rx_stop_dma(struct ti_csi2rx_ctx *ctx)
        dma->state = TI_CSI2RX_DMA_STOPPED;
        spin_unlock_irqrestore(&dma->lock, flags);
 
+       init_completion(&csi->drain_complete);
+
        if (state != TI_CSI2RX_DMA_STOPPED) {
                /*
                 * Normal DMA termination does not clean up pending data on

@@ -796,6 +803,10 @@ static void ti_csi2rx_stop_dma(struct ti_csi2rx_ctx *ctx)
                                 "Failed to drain DMA. Next frame might be bogus\n");
        }
 
+       if (!wait_for_completion_timeout(&csi->drain_complete,
+                                        msecs_to_jiffies(DRAIN_TIMEOUT_MS)))
+               dev_dbg(csi->dev, "DMA transfer timed out for drain buffer\n");
+
        ret = dmaengine_terminate_sync(ctx->dma.chan);
        if (ret)
                dev_err(ctx->csi->dev, "Failed to stop DMA: %d\n", ret);

-- 
2.34.1