linux-kernel - Re: [PATCH v5] spi: spi-imx: add DMA support

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Date:	Wed, 10 Sep 2014 19:22:59 +0800
From:	Robin Gong <b38343@...escale.com>
To:	Mark Brown <broonie@...nel.org>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	<linux-spi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<marex@...x.de>, <shawn.guo@...aro.org>, <Frank.Li@...escale.com>
Subject: Re: [PATCH v5] spi: spi-imx: add DMA support

On Wed, Sep 10, 2014 at 11:21:05AM +0100, Mark Brown wrote:
> On Wed, Sep 10, 2014 at 09:30:04AM +0800, Robin Gong wrote:
> 
> > +static bool spi_imx_can_dma(struct spi_master *master, struct spi_device *spi,
> > +			 struct spi_transfer *transfer)
> > +{
> > +	struct spi_imx_data *spi_imx = spi_master_get_devdata(master);
> > +
> > +	if (spi_imx->dma_is_inited && (transfer->len > spi_imx->rx_wml)
> > +	    && (transfer->len > spi_imx->tx_wml))
> > +		spi_imx->usedma = true;
> > +	else
> > +		spi_imx->usedma = false;
> > +
> > +	return spi_imx->usedma;
> > +}
> 
> This isn't going to work, anything that looks at the usedma flag will
> see the result of the last thing that was checked which may or may not
> be the transfer that it's handling.  The driver should check to see if
> the core mapped the transfer for DMA.
Yes, you're right. I should use "transfer->tx_sg->sgl == NULL" or
"transfer->rx_sg->sgl == NULL" instead of usedma flag in driver, right?

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