linux-kernel - [PATCH v2 03/19] spi: dw: Clear DMAC register when done or stopped

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Date:   Fri, 15 May 2020 13:47:42 +0300
From:   Serge Semin <Sergey.Semin@...kalelectronics.ru>
To:     Mark Brown <broonie@...nel.org>
CC:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Serge Semin <fancer.lancer@...il.com>,
        Georgy Vlasov <Georgy.Vlasov@...kalelectronics.ru>,
        Ramil Zaripov <Ramil.Zaripov@...kalelectronics.ru>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Paul Burton <paulburton@...nel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Arnd Bergmann <arnd@...db.de>,
        Allison Randal <allison@...utok.net>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Gareth Williams <gareth.williams.jx@...esas.com>,
        Rob Herring <robh+dt@...nel.org>, <linux-mips@...r.kernel.org>,
        <devicetree@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>,
        Wan Ahmad Zainie <wan.ahmad.zainie.wan.mohamad@...el.com>,
        Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        <linux-spi@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH v2 03/19] 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@...kalelectronics.ru>
Signed-off-by: Georgy Vlasov <Georgy.Vlasov@...kalelectronics.ru>
Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
Cc: Ramil Zaripov <Ramil.Zaripov@...kalelectronics.ru>
Cc: Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>
Cc: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc: Paul Burton <paulburton@...nel.org>
Cc: Ralf Baechle <ralf@...ux-mips.org>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Allison Randal <allison@...utok.net>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Gareth Williams <gareth.williams.jx@...esas.com>
Cc: Rob Herring <robh+dt@...nel.org>
Cc: linux-mips@...r.kernel.org
Cc: devicetree@...r.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