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

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Message-ID: <20140910151759.GA31462@Robin-OptiPlex-780>
Date:	Wed, 10 Sep 2014 23:18:01 +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 12:45:30PM +0100, Mark Brown wrote:
> On Wed, Sep 10, 2014 at 07:22:59PM +0800, Robin Gong wrote:
> > On Wed, Sep 10, 2014 at 11:21:05AM +0100, Mark Brown wrote:
> 
> > > 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?
> 
> Right.
But looks spi core framework can make sure every rx or tx transfer in sequence.
If so, can_dma will never be called until this transfer finished
(spi_pump_messages), and my usedma flag also never be modified until next
transfer start. Please correct me if I am wrong, thanks.

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