[4.14,092/190] spi: dw: Fix Rx-only DMA transfers

Commit Message

Greg KH June 19, 2020, 2:32 p.m. UTC

From: Serge Semin <[e-mail]>

[ Upstream commit 46164fde6b7890e7a3982d54549947c8394c0192 ]

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 <[e-mail]>
Reviewed-by: Andy Shevchenko <[e-mail]>
Cc: Georgy Vlasov <[e-mail]>
Cc: Ramil Zaripov <[e-mail]>
Cc: Alexey Malahov <[e-mail]>
Cc: Thomas Bogendoerfer <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Feng Tang <[e-mail]>
Cc: Rob Herring <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>
Signed-off-by: Sasha Levin <[e-mail]>
---
 drivers/spi/spi-dw.c | 1 +
 1 file changed, 1 insertion(+)

Patch

diff --git a/drivers/spi/spi-dw.c b/drivers/spi/spi-dw.c
index b11d0cd3fd20..9fcee7273a79 100644
--- a/drivers/spi/spi-dw.c
+++ b/drivers/spi/spi-dw.c
@@ -531,6 +531,7 @@  int dw_spi_add_host(struct device *dev, struct dw_spi *dws)
 			dws->dma_inited = 0;
 		} else {
 			master->can_dma = dws->dma_ops->can_dma;
+			master->flags |= SPI_CONTROLLER_MUST_TX;
 		}
 	}