From: Serge Semin Sergey.Semin@baikalelectronics.ru
[ 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 Sergey.Semin@baikalelectronics.ru Reviewed-by: Andy Shevchenko andriy.shevchenko@linux.intel.com Cc: Georgy Vlasov Georgy.Vlasov@baikalelectronics.ru Cc: Ramil Zaripov Ramil.Zaripov@baikalelectronics.ru Cc: Alexey Malahov Alexey.Malahov@baikalelectronics.ru Cc: Thomas Bogendoerfer tsbogend@alpha.franken.de Cc: Arnd Bergmann arnd@arndb.de Cc: Feng Tang feng.tang@intel.com Cc: Rob Herring robh+dt@kernel.org Cc: linux-mips@vger.kernel.org Cc: devicetree@vger.kernel.org Link: https://lore.kernel.org/r/20200529131205.31838-9-Sergey.Semin@baikalelectron... Signed-off-by: Mark Brown broonie@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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 dbf9b8d5cebe..5725c37544f2 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; } }