dmaengine: imx-sdma - correct the dma transfer residue calculation

The residue calculation was taking in consideration that dma
transaction status will be always retrieved in the dma callback
used to inform that dma transfer is complete. However this is not
the case for all subsystems that use dma. Some subsystems use a
timer to check the dma status periodically.

Therefore the calculation was updated and residue is calculated
accordingly by a) update the residue calculation taking in
consideration the last used buffer index by using *buf_ptail* variable
and b) chn_real_count (number of bytes transferred) is initialized to
zero, when dma channel is created, to avoid using an uninitialized
value in residue calculation when dma status is checked without
waiting dma complete event.

Signed-off-by: Nandor Han <nandor.han@ge.com>
Acked-by: Peter Senna Tschudin <peter.senna@collabora.com>
Tested-by: Peter Senna Tschudin <peter.senna@collabora.com>
Tested-by: Marek Vasut <marex@denx.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

1 files changed, 9 insertions, 4 deletions

diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
index b9629b2bfc05..d1651a50c349 100644
--- a/drivers/dma/imx-sdma.c
+++ b/drivers/dma/imx-sdma.c
@@ -298,6 +298,7 @@ struct sdma_engine;
  * @event_id1           for channels that use 2 events
  * @word_size           peripheral access size
  * @buf_tail            ID of the buffer that was processed
+ * @buf_ptail           ID of the previous buffer that was processed
  * @num_bd              max NUM_BD. number of descriptors currently handling
  */
 struct sdma_channel {
@@ -309,6 +310,7 @@ struct sdma_channel {
         unsigned int                    event_id1;
         enum dma_slave_buswidth         word_size;
         unsigned int                    buf_tail;
+        unsigned int                    buf_ptail;
         unsigned int                    num_bd;
         unsigned int                    period_len;
         struct sdma_buffer_descriptor   *bd;
@@ -700,6 +702,8 @@ static void sdma_update_channel_loop(struct sdma_channel *sdmac)
                 sdmac->chn_real_count = bd->mode.count;
                 bd->mode.status |= BD_DONE;
                 bd->mode.count = sdmac->period_len;
+                sdmac->buf_ptail = sdmac->buf_tail;
+                sdmac->buf_tail = (sdmac->buf_tail + 1) % sdmac->num_bd;
 
                 /*
                  * The callback is called from the interrupt context in order
@@ -710,9 +714,6 @@ static void sdma_update_channel_loop(struct sdma_channel *sdmac)
 
                 dmaengine_desc_get_callback_invoke(&sdmac->desc, NULL);
 
-                sdmac->buf_tail++;
-                sdmac->buf_tail %= sdmac->num_bd;
-
                 if (error)
                         sdmac->status = old_status;
         }
@@ -1186,6 +1187,8 @@ static struct dma_async_tx_descriptor *sdma_prep_slave_sg(
         sdmac->flags = 0;
 
         sdmac->buf_tail = 0;
+        sdmac->buf_ptail = 0;
+        sdmac->chn_real_count = 0;
 
         dev_dbg(sdma->dev, "setting up %d entries for channel %d.\n",
                         sg_len, channel);
@@ -1288,6 +1291,8 @@ static struct dma_async_tx_descriptor *sdma_prep_dma_cyclic(
         sdmac->status = DMA_IN_PROGRESS;
 
         sdmac->buf_tail = 0;
+        sdmac->buf_ptail = 0;
+        sdmac->chn_real_count = 0;
         sdmac->period_len = period_len;
 
         sdmac->flags |= IMX_DMA_SG_LOOP;
@@ -1385,7 +1390,7 @@ static enum dma_status sdma_tx_status(struct dma_chan *chan,
         u32 residue;
 
         if (sdmac->flags & IMX_DMA_SG_LOOP)
-                residue = (sdmac->num_bd - sdmac->buf_tail) *
+                residue = (sdmac->num_bd - sdmac->buf_ptail) *
                            sdmac->period_len - sdmac->chn_real_count;
         else
                 residue = sdmac->chn_count - sdmac->chn_real_count;