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Merge remote-tracking branch 'spi/for-5.8' into spi-linus

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Mark Brown 2020-07-29 14:51:58 +01:00
commit 8ade0c2fab
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1 changed files with 13 additions and 1 deletions
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14
drivers/spi/spi-dw-dma.c
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@ -372,8 +372,20 @@ static int dw_spi_dma_setup(struct dw_spi *dws, struct spi_transfer *xfer)
{
u16 imr = 0, dma_ctrl = 0;
/*
* Having a Rx DMA channel serviced with higher priority than a Tx DMA
* channel might not be enough to provide a well balanced DMA-based
* SPI transfer interface. There might still be moments when the Tx DMA
* channel is occasionally handled faster than the Rx DMA channel.
* That in its turn will eventually cause the SPI Rx FIFO overflow if
* SPI bus speed is high enough to fill the SPI Rx FIFO in before it's
* cleared by the Rx DMA channel. In order to fix the problem the Tx
* DMA activity is intentionally slowed down by limiting the SPI Tx
* FIFO depth with a value twice bigger than the Tx burst length
* calculated earlier by the dw_spi_dma_maxburst_init() method.
*/
dw_writel(dws, DW_SPI_DMARDLR, dws->rxburst - 1);
dw_writel(dws, DW_SPI_DMATDLR, dws->fifo_len - dws->txburst);
dw_writel(dws, DW_SPI_DMATDLR, dws->txburst);
if (xfer->tx_buf)
dma_ctrl |= SPI_DMA_TDMAE;