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Subject[PATCH v6 08/16] spi: dw: Fix Rx-only DMA transfers
Tx-only DMA transfers are working perfectly fine since in this case
the code just ignores the Rx FIFO overflow interrupts. But it turns
out the SPI Rx-only transfers are broken since nothing pushing any
data to the shift registers, so the Rx FIFO is left empty and the
SPI core subsystems just returns a timeout error. Since DW DMAC
driver doesn't support something like cyclic write operations of
a single byte to a device register, the only way to support the
Rx-only SPI transfers is to fake it by using a dummy Tx-buffer.
This is what we intend to fix in this commit by setting the
SPI_CONTROLLER_MUST_TX flag for DMA-capable platform.

Signed-off-by: Serge Semin <>
Reviewed-by: Andy Shevchenko <>
Cc: Georgy Vlasov <>
Cc: Ramil Zaripov <>
Cc: Alexey Malahov <>
Cc: Thomas Bogendoerfer <>
Cc: Arnd Bergmann <>
Cc: Feng Tang <>
Cc: Rob Herring <>
drivers/spi/spi-dw.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/drivers/spi/spi-dw.c b/drivers/spi/spi-dw.c
index 6939e003e3e9..4d1849699a12 100644
--- a/drivers/spi/spi-dw.c
+++ b/drivers/spi/spi-dw.c
@@ -515,6 +515,7 @@ int dw_spi_add_host(struct device *dev, struct dw_spi *dws)
dev_warn(dev, "DMA init failed\n");
} else {
master->can_dma = dws->dma_ops->can_dma;
+ master->flags |= SPI_CONTROLLER_MUST_TX;

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