linux-kernel - Re: [PATCH v5] spi: spi-ti-qspi: Add DMA support for QSPI mmap read

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Message-ID: <20160809113329.GA9347@sirena.org.uk>
Date:	Tue, 9 Aug 2016 12:33:29 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Vignesh R <vigneshr@...com>
Cc:	linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-omap@...r.kernel.org
Subject: Re: [PATCH v5] spi: spi-ti-qspi: Add DMA support for QSPI mmap read

On Tue, Aug 09, 2016 at 04:33:11PM +0530, Vignesh R wrote:

> +static int ti_qspi_map_buf(struct ti_qspi *qspi, void *buf,
> +			   unsigned int len, struct sg_table *sgt)
> +{
> +	unsigned int max_seg_size =
> +		dma_get_max_seg_size(qspi->rx_chan->device->dev);
> +	unsigned int desc_len = min_t(int, max_seg_size, PAGE_SIZE);
> +	int sgs = DIV_ROUND_UP(len + offset_in_page(buf), desc_len);
> +	struct page *vm_page;
> +	size_t min;
> +	int i, ret;
> +
> +	ret = sg_alloc_table(sgt, sgs, GFP_KERNEL);
> +	if (ret)
> +		return ret;
> +
> +	for (i = 0; i < sgs; i++) {
> +		min = min_t(size_t, len, desc_len -
> +			    offset_in_page(buf));
> +		vm_page = kmap_to_page(buf);
> +		if (!vm_page) {
> +			sg_free_table(sgt);
> +			return -ENOMEM;
> +		}
> +		sg_set_page(&sgt->sgl[i], vm_page, min,
> +			    offset_in_page(buf));
> +		buf += min;
> +		len -= min;

This looks a lot like the core code for mapping the buffers - why is
this open coded rather than reused?

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