On Fri, May 15, 2020 at 01:47:51PM +0300, Serge Semin wrote: > 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.
I'm fine with this if Mark considers this right thing to do. So, conditionally Reviewed-by: Andy Shevchenko <[email protected]> > > Signed-off-by: Serge Semin <[email protected]> > Cc: Georgy Vlasov <[email protected]> > Cc: Ramil Zaripov <[email protected]> > Cc: Alexey Malahov <[email protected]> > Cc: Thomas Bogendoerfer <[email protected]> > Cc: Paul Burton <[email protected]> > Cc: Ralf Baechle <[email protected]> > Cc: Arnd Bergmann <[email protected]> > Cc: Allison Randal <[email protected]> > Cc: Andy Shevchenko <[email protected]> > Cc: Gareth Williams <[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 1edb8cdd11ee..31607b40147d 100644 > --- a/drivers/spi/spi-dw.c > +++ b/drivers/spi/spi-dw.c > @@ -517,6 +517,7 @@ 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; > } > } > > -- > 2.25.1 > -- With Best Regards, Andy Shevchenko
