linux-kernel - Re: [PATCH 6/6] spi: sun4i: add DMA transfers support

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Message-ID: <20180403081711.rqsp77mgnuvlnzt5@flea>
Date:   Tue, 3 Apr 2018 10:17:11 +0200
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Sergey Suloev <ssuloev@...altech.com>
Cc:     Mark Brown <broonie@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        linux-spi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/6] spi: sun4i: add DMA transfers support

On Thu, Mar 29, 2018 at 09:59:07PM +0300, Sergey Suloev wrote:
> +static int sun4i_spi_dma_setup(struct device *dev,
> +			       struct resource *res)
> +{
> +	struct spi_master *master = dev_get_drvdata(dev);
> +	struct dma_slave_config dma_sconf;
> +	int ret;
> +
> +	master->dma_tx = dma_request_slave_channel_reason(dev, "tx");
> +	if (IS_ERR(master->dma_tx)) {
> +		dev_err(dev, "Unable to acquire DMA TX channel\n");
> +		ret = PTR_ERR(master->dma_tx);
> +		goto out;
> +	}
> +
> +	dma_sconf.direction = DMA_MEM_TO_DEV;
> +	dma_sconf.src_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
> +	dma_sconf.dst_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;

I guess that would depend on the size of the transfer, right?

> +	dma_sconf.dst_addr = res->start + SUN4I_TXDATA_REG;
> +	dma_sconf.dst_maxburst = 1;
> +	dma_sconf.src_maxburst = 1;

And a burst of 1 seems sub-optimal here.

> +	ret = sun4i_spi_dma_setup(&pdev->dev, res);
> +	if (ret) {
> +		if (ret == -EPROBE_DEFER) {
> +			/* wait for the dma driver to load */
> +			goto err_free_master;
> +		}
> +		dev_warn(&pdev->dev, "DMA transfer not supported\n");

Saying why it's not supported would be great.

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

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