spi: dw: Clear DMAC register when done or stopped

If DMAC register is left uncleared any further DMAless transfers
may cause the DMAC hardware handshaking interface getting activated.
So the next DMA-based Rx/Tx transaction will be started right
after the dma_async_issue_pending() method is invoked even if no
DMATDLR/DMARDLR conditions are met. This at the same time may cause
the Tx/Rx FIFO buffers underrun/overrun. In order to fix this we
must clear DMAC register after a current DMA-based transaction is
finished.

Co-developed-by: Georgy Vlasov <Georgy.Vlasov@baikalelectronics.ru>
Signed-off-by: Georgy Vlasov <Georgy.Vlasov@baikalelectronics.ru>
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200515104758.6934-4-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/spi/spi-dw-mid.c b/drivers/spi/spi-dw-mid.c
index 177e1f5ec62b2e51942ea5c1fd0a93f97f524d83..f9757a37069918eadf994b0f6c3006fb1271c0c0 100644 (file)
--- a/drivers/spi/spi-dw-mid.c
+++ b/drivers/spi/spi-dw-mid.c
@@ -106,6 +106,8 @@ static void mid_spi_dma_exit(struct dw_spi *dws)
                dmaengine_terminate_sync(dws->rxchan);
                dma_release_channel(dws->rxchan);
        }
+
+       dw_writel(dws, DW_SPI_DMACR, 0);
 }
 
 static irqreturn_t dma_transfer(struct dw_spi *dws)
@@ -152,6 +154,8 @@ static void dw_spi_dma_tx_done(void *arg)
        clear_bit(TX_BUSY, &dws->dma_chan_busy);
        if (test_bit(RX_BUSY, &dws->dma_chan_busy))
                return;
+
+       dw_writel(dws, DW_SPI_DMACR, 0);
        spi_finalize_current_transfer(dws->master);
 }
 
@@ -199,6 +203,8 @@ static void dw_spi_dma_rx_done(void *arg)
        clear_bit(RX_BUSY, &dws->dma_chan_busy);
        if (test_bit(TX_BUSY, &dws->dma_chan_busy))
                return;
+
+       dw_writel(dws, DW_SPI_DMACR, 0);
        spi_finalize_current_transfer(dws->master);
 }
 
@@ -292,6 +298,8 @@ static void mid_spi_dma_stop(struct dw_spi *dws)
                dmaengine_terminate_sync(dws->rxchan);
                clear_bit(RX_BUSY, &dws->dma_chan_busy);
        }
+
+       dw_writel(dws, DW_SPI_DMACR, 0);
 }
 
 static const struct dw_spi_dma_ops mfld_dma_ops = {