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From:   Robin Gong <yibin.gong@nxp.com>
To:     Mark Brown <broonie@kernel.org>
CC:     Vinod Koul <vkoul@kernel.org>,
        "shawnguo@kernel.org" <shawnguo@kernel.org>,
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Subject: RE: [PATCH v1 RFC 1/2] spi: introduce fallback to pio
Thread-Topic: [PATCH v1 RFC 1/2] spi: introduce fallback to pio
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Date:   Mon, 15 Jun 2020 14:53:29 +0000
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On 2020/06/15 22:36 Mark Brown <broonie@kernel.org> wrote:=20
> On Mon, Jun 15, 2020 at 02:18:54PM +0000, Robin Gong wrote:
> > Seems not easy to find a suitable error value, how about EBADR which
> > sounds like no any available dma_async_tx_descriptor got by calling
> dmaengine_prep_slave_sg?
>=20
> > #define EBADR           53      /* Invalid request descriptor */
>=20
> We could also pass in a flag that could be set separately to the error co=
de to
> indicate that nothing had happened to the hardware yet.
Do you mean spi-imx.c checking 'ctlr->flags' before return such error code?
Or just like below done in spi.c.
+fallback_pio:
                        ret =3D ctlr->transfer_one(ctlr, msg->spi, xfer);
                        if (ret < 0) {
+                               if (ret =3D=3D - EBADR && ctlr->cur_msg_map=
ped &&
+                                  (ctlr->flags & SPI_CONTROLLER_FALLBACK))=
 {
+                                       __spi_unmap_msg(ctlr, msg);
+                                       ctlr->fallback =3D true;
+                                       goto fallback_pio;
+                               }
+