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Subject: RE: [PATCH v9 RESEND 01/13] spi: imx: add dma_sync_sg_for_device
 after fallback from dma
Thread-Topic: [PATCH v9 RESEND 01/13] spi: imx: add dma_sync_sg_for_device
 after fallback from dma
Thread-Index: AQHWPBYcMy4ZpJEEjkym0JBjSJknZajOy8sAgAABToA=
Date:   Mon, 8 Jun 2020 15:08:45 +0000
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 <20200608143458.GH4593@sirena.org.uk>
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On 2020/06/08 22:35 Mark Brown <broonie@kernel.org> wrote:
> On Sun, Jun 07, 2020 at 07:21:05AM +0800, Robin Gong wrote:
> > In case dma transfer failed and fallback to pio, tx_buf/rx_buf need to
> > be taken care cache since they have already been maintained by spi.c
>=20
> Is this needed as part of this series?  This looks like an independent fi=
x and it
> seems better to get this in independently.
But that's used to fix one patch [05/13]of the v8 patch set. To be honest, =
I'm also
not sure how to handle it so that I merged both into first v9....For now, I=
 think you
are right, since 'fallback pio' patch could be independent this series. Wil=
l resend in
v10.
>=20
> > Fixes: bcd8e7761ec9("spi: imx: fallback to PIO if dma setup failure")
> > Signed-off-by: Robin Gong <yibin.gong@nxp.com>
> > Reported-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
> > Link:
> > https://lore.kernel.org/linux-arm-kernel/5d246dd81607bb6e5cb9af86ad4e5
> > 3f7a7a99c50.camel@ew.tq-group.com/
>=20
> The Link is usually to the patch on the list.
Okay, will remove it.
>=20
> > --- a/drivers/spi/spi-imx.c
> > +++ b/drivers/spi/spi-imx.c
> > @@ -1456,6 +1456,13 @@ static int spi_imx_pio_transfer(struct spi_devic=
e
> *spi,
> >  		return -ETIMEDOUT;
> >  	}
> >
> > +	if (transfer->rx_sg.sgl) {
> > +		struct device *rx_dev =3D spi->controller->dma_rx->device->dev;
> > +
> > +		dma_sync_sg_for_device(rx_dev, transfer->rx_sg.sgl,
> > +				       transfer->rx_sg.nents, DMA_TO_DEVICE);
> > +	}
> > +
> >  	return transfer->len;
> >  }
>=20
> This is confusing - why are we DMA mapping to the device after doing a PI=
O
> transfer?
'transfer->rx_sg.sgl' condition check that's the case fallback PIO after DM=
A transfer
failed. But the spi core still think the buffer should be in 'device' while=
 spi driver
touch it by PIO(CPU), so sync it back to device to ensure all received data=
 flush to DDR.
 =20