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

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Message-ID: <VE1PR04MB6638D0C9FE0289FFE13ABA49899C0@VE1PR04MB6638.eurprd04.prod.outlook.com>
Date:   Mon, 15 Jun 2020 14:53:29 +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 22:36 Mark Brown <broonie@...nel.org> wrote: 
> 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?
> 
> > #define EBADR           53      /* Invalid request descriptor */
> 
> We could also pass in a flag that could be set separately to the error code 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 = ctlr->transfer_one(ctlr, msg->spi, xfer);
                        if (ret < 0) {
+                               if (ret == - EBADR && ctlr->cur_msg_mapped &&
+                                  (ctlr->flags & SPI_CONTROLLER_FALLBACK)) {
+                                       __spi_unmap_msg(ctlr, msg);
+                                       ctlr->fallback = true;
+                                       goto fallback_pio;
+                               }
+