linux-kernel - Re: [PATCH 4/9] spi: sun4i: add DMA support

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Message-ID: <20150820185850.GQ12027@sirena.org.uk>
Date:	Thu, 20 Aug 2015 11:58:50 -0700
From:	Mark Brown <broonie@...nel.org>
To:	Emilio López <emilio@...pez.com.ar>
Cc:	linux-sunxi@...glegroups.com, Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org
Subject: Re: [PATCH 4/9] spi: sun4i: add DMA support

On Thu, Aug 20, 2015 at 02:19:46PM -0000, Emilio López wrote:

> -	sun4i_spi_drain_fifo(sspi, SUN4I_FIFO_DEPTH);
> +	if (sun4i_spi_can_dma(master, spi, tfr) && desc_rx) {
> +		/* The receive transfer should be the last one to finish */
> +		dma_wait_for_async_tx(desc_rx);

What if it's a transmit only transfer?  We'll fall over to this...

> +	} else {
> +		sun4i_spi_drain_fifo(sspi, SUN4I_FIFO_DEPTH);
> +	}

...which manually reads data from the FIFO which doesn't seem like what
we want, won't it conflict with the DMA?

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