linux-kernel - RE: [EXT] Re: [PATCH 5/6] spi: imx: support dynamic burst length for ECSPI DMA mode

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Message-ID:
 <VI2PR04MB111470B46C3B7B6AF66B69D07E8DEA@VI2PR04MB11147.eurprd04.prod.outlook.com>
Date: Wed, 26 Nov 2025 12:29:35 +0000
From: Carlos Song <carlos.song@....com>
To: Marc Kleine-Budde <mkl@...gutronix.de>
CC: "broonie@...nel.org" <broonie@...nel.org>, Frank Li <frank.li@....com>,
	"hawnguo@...nel.org" <hawnguo@...nel.org>, "s.hauer@...gutronix.de"
	<s.hauer@...gutronix.de>, "kernel@...gutronix.de" <kernel@...gutronix.de>,
	"festevam@...il.com" <festevam@...il.com>, "linux-spi@...r.kernel.org"
	<linux-spi@...r.kernel.org>, "imx@...ts.linux.dev" <imx@...ts.linux.dev>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [EXT] Re: [PATCH 5/6] spi: imx: support dynamic burst length for
 ECSPI DMA mode



> -----Original Message-----
> From: Marc Kleine-Budde <mkl@...gutronix.de>
> Sent: Wednesday, November 26, 2025 8:23 PM
> To: Carlos Song <carlos.song@....com>
> Cc: broonie@...nel.org; Frank Li <frank.li@....com>; hawnguo@...nel.org;
> s.hauer@...gutronix.de; kernel@...gutronix.de; festevam@...il.com;
> linux-spi@...r.kernel.org; imx@...ts.linux.dev;
> linux-arm-kernel@...ts.infradead.org; linux-kernel@...r.kernel.org
> Subject: [EXT] Re: [PATCH 5/6] spi: imx: support dynamic burst length for ECSPI
> DMA mode
> 
> On 25.11.2025 18:06:17, Carlos Song wrote:
> >  static int spi_imx_pio_transfer(struct spi_device *spi,
> >  				struct spi_transfer *transfer)
> >  {
> > @@ -1780,9 +2112,14 @@ static int spi_imx_transfer_one(struct
> spi_controller *controller,
> >  	 * transfer, the SPI transfer has already been mapped, so we
> >  	 * have to do the DMA transfer here.
> >  	 */
> > -	if (spi_imx->usedma)
> > -		return spi_imx_dma_transfer(spi_imx, transfer);
> > -
> > +	if (spi_imx->usedma) {
> > +		ret = spi_imx_dma_transfer(spi_imx, transfer);
> > +		if (transfer->error & SPI_TRANS_FAIL_NO_START) {
> > +			spi_imx->usedma = false;
> > +			return spi_imx_pio_transfer(spi, transfer);
> > +		}
> > +		return ret;
> > +	}
> 
> Why do you do this? AFAICS the framework already does this for you see:
> spi_transfer_one_message().
> 
Hi,

In frame work:
				if ((xfer->tx_sg_mapped || xfer->rx_sg_mapped) &&
				    (xfer->error & SPI_TRANS_FAIL_NO_START)) {
					__spi_unmap_msg(ctlr, msg);
					ctlr->fallback = true;
					xfer->error &= ~SPI_TRANS_FAIL_NO_START;
					goto fallback_pio;
				}

It only will help do this for "framework finished DMA map case". But DMA dynamic burst feature is mapped in driver.
So this condition never meet: (xfer->tx_sg_mapped || xfer->rx_sg_mapped) I think..
Carlos

> Marc
> 
> --
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