Re: [PATCH 4.19 182/267] spi: dw: Return any value retrieved from the dma_transfer callback

[Ralph Siemsen]

Hi Serge, Pavel, Greg,

On Mon, Jun 22, 2020 at 11:51:21PM +0300, Serge Semin wrote:
> Hello Pavel
>
> On Fri, Jun 19, 2020 at 11:07:19PM +0200, Pavel Machek wrote:
>
> > Mainline patch simply changes return value, but code is different in
> > v4.19, and poll_transfer will now be avoided when dws->dma_mapped. Is
> > that a problem?
>
> Actually no.) In that old 4.19 context it's even better to return straight away
> no matter what value is returned by the dma_transfer() callback.

This patch changes the return dma_transfer return value from 0 to 1, 
however it was only done in spi-dw-mid.c func mid_spi_dma_transfer().

There is an identical function in spi-dw-mmio.c that needs the same 
treatment, otherwise access to the SPI device becomes erratic and even 
causes kernel to hang. Guess how I found this ;-)

So the following patch is needed as well, at least in 4.9 and 4.19, I 
did not check/test other versions. Mainline does not need this, since 
the code seems to have been refactored to avoid the duplication.

Regards,
-Ralph

diff --git a/drivers/spi/spi-dw-mmio.c b/drivers/spi/spi-dw-mmio.c
index c563c2815093..99641c485288 100644
--- a/drivers/spi/spi-dw-mmio.c
+++ b/drivers/spi/spi-dw-mmio.c
@@ -358,7 +358,7 @@ static int mmio_spi_dma_transfer(struct dw_spi *dws, struct spi_transfer *xfer)
		dma_async_issue_pending(dws->txchan);
	}

-	return 0;
+	return 1;
}

static void mmio_spi_dma_stop(struct dw_spi *dws)
--
2.17.1