linux-kernel - RE: [PATCH v1 RFC 1/2] spi: introduce fallback to pio

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Date:   Tue, 16 Jun 2020 02:03:40 +0000
From:   Robin Gong <yibin.gong@....com>
To:     Mark Brown <broonie@...nel.org>
CC:     Vinod Koul <vkoul@...nel.org>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "matthias.schiffer@...tq-group.com" 
        <matthias.schiffer@...tq-group.com>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        dl-linux-imx <linux-imx@....com>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v1 RFC 1/2] spi: introduce fallback to pio

On 2020/06/15 22:56 Mark Brown <broonie@...nel.org> wrote: 
> On Mon, Jun 15, 2020 at 02:53:29PM +0000, Robin Gong wrote: 
> > Do you mean spi-imx.c checking 'ctlr->flags' before return such error code?
> > Or just like below done in spi.c.
> 
> No, I mean passing in an additional argument which can provide richer data
> than trying to smash things into the return value.
Okay, how about adding this additional argument in struct spi_transfer like below?
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 95291fe4..7c19099 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -943,6 +943,9 @@ struct spi_transfer {
        bool            timestamped;

        struct list_head transfer_list;
+
+#define        SPI_TRANS_DMA_PREP_FAIL BIT(3)  /* prepare dma failed */
+       u16             flags;
 };

While spi core checking it as below after it set in spi-imx.c:
fallback_pio:
        ret = ctlr->transfer_one(ctlr, msg->spi, xfer);
        if (ret < 0) {
                 if (ctlr->cur_msg_mapped &&
                   (xfer->flags & SPI_TRANS_DMA_PREP_FAIL)) {
                   __spi_unmap_msg(ctlr, msg);
                   ctlr->fallback = true;
                   xfer->flags &= ~SPI_TRANS_DMA_PREP_FAIL;
                   goto fallback_pio;
                 }