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 <[email protected]> Reviewed-by: Andy Shevchenko <[email protected]> Cc: Georgy Vlasov <[email protected]> Cc: Ramil Zaripov <[email protected]> Cc: Alexey Malahov <[email protected]> Cc: Thomas Bogendoerfer <[email protected]> Cc: Arnd Bergmann <[email protected]> Cc: Feng Tang <[email protected]> Cc: Rob Herring <[email protected]> Cc: [email protected] Cc: [email protected] --- 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; } } -- 2.26.2
