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 <redacted>
Signed-off-by: Georgy Vlasov <redacted>
Signed-off-by: Serge Semin <redacted>
Cc: Ramil Zaripov <redacted>
Cc: Alexey Malahov <redacted>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Paul Burton <paulburton@kernel.org>
Cc: Ralf Baechle <redacted>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Allison Randal <redacted>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Gareth Williams <redacted>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: devicetree@vger.kernel.org

---

Changelog v2:
- Move the patch to the head of the series so one could be picked up to
  the stable kernels as a fix.
- Clear the DMACR in the DMA exit callback too.
---
 drivers/spi/spi-dw-mid.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/spi/spi-dw-mid.c b/drivers/spi/spi-dw-mid.c
index 7a5ae1506365..0c597b6bb154 100644
--- a/drivers/spi/spi-dw-mid.c
+++ b/drivers/spi/spi-dw-mid.c

@@ -108,6 +108,8 @@ 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)

@@ -178,6 +180,8 @@ 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);
 }
 

@@ -249,6 +253,8 @@ 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);
 }
 

@@ -342,6 +348,8 @@ 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 = {

-- 
2.25.1