From: Serge Semin <Sergey.Semin@xxxxxxxxxxxxxxxxxxxx> [ 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@xxxxxxxxxxxxxxxxxxxx> Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> Cc: Georgy Vlasov <Georgy.Vlasov@xxxxxxxxxxxxxxxxxxxx> Cc: Ramil Zaripov <Ramil.Zaripov@xxxxxxxxxxxxxxxxxxxx> Cc: Alexey Malahov <Alexey.Malahov@xxxxxxxxxxxxxxxxxxxx> Cc: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx> Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: Feng Tang <feng.tang@xxxxxxxxx> Cc: Rob Herring <robh+dt@xxxxxxxxxx> Cc: linux-mips@xxxxxxxxxxxxxxx Cc: devicetree@xxxxxxxxxxxxxxx Link: https://lore.kernel.org/r/20200529131205.31838-9-Sergey.Semin@xxxxxxxxxxxxxxxxxxxx Signed-off-by: Mark Brown <broonie@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- 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 b461200871f8..26ed3b4233a2 100644 --- a/drivers/spi/spi-dw.c +++ b/drivers/spi/spi-dw.c @@ -526,6 +526,7 @@ 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; } } -- 2.25.1
