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 <andriy.shevche...@linux.intel.com>
>
> Signed-off-by: Serge Semin <sergey.se...@baikalelectronics.ru>
> Cc: Georgy Vlasov <georgy.vla...@baikalelectronics.ru>
> Cc: Ramil Zaripov <ramil.zari...@baikalelectronics.ru>
> Cc: Alexey Malahov <alexey.mala...@baikalelectronics.ru>
> Cc: Thomas Bogendoerfer <tsbog...@alpha.franken.de>
> Cc: Paul Burton <paulbur...@kernel.org>
> Cc: Ralf Baechle <r...@linux-mips.org>
> Cc: Arnd Bergmann <a...@arndb.de>
> Cc: Allison Randal <alli...@lohutok.net>
> Cc: Andy Shevchenko <andriy.shevche...@linux.intel.com>
> Cc: Gareth Williams <gareth.williams...@renesas.com>
> Cc: Rob Herring <robh...@kernel.org>
> Cc: linux-m...@vger.kernel.org
> Cc: devicet...@vger.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 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
