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Subject: Re: [PATCH 2/3] mtd: mediatek: driver for MTK Smart Device Gen1 NAND
To: Boris Brezillon <boris.brezillon@free-electrons.com>
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From: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@linaro.org>
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Date: Tue, 15 Mar 2016 08:28:37 -0400
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On 03/08/2016 11:24 AM, Boris Brezillon wrote:
>> +static int mtk_nfc_write_page(struct mtd_info *mtd,
>> > +			struct nand_chip *chip, const uint8_t *buf,
>> > +			int oob_on, int page, int raw)
>> > +{
>> > +
>> > +	struct mtk_nfc_host *host = nand_get_controller_data(chip);
>> > +	struct completion *nfi = &host->nfi.complete;
>> > +	struct device *dev = host->dev;
>> > +	const bool use_ecc = !raw;
>> > +	void *q = (void *) buf;
>> > +	dma_addr_t dma_addr;
>> > +	size_t dmasize;
>> > +	u32 reg;
>> > +	int ret;
>> > +
>> > +	dmasize = mtd->writesize + (raw ? mtd->oobsize : 0);
>> > +
>> > +	dma_addr = dma_map_single(dev, q, dmasize, DMA_TO_DEVICE);
> buf is not guaranteed to be physically contiguous, so you can't just
> use it with DMA without doing a few more verifications.
>
> In case you're interested in using a generic approach to do this
> verification, you can have a look at this series [2].
>

unfortunately the internal dma controller does not support scatter gather
operations (we need to DMA in/out of memory in a single shot)
If we enable NAND_USE_BOUNCE_BUFFER, I think this guarantees that the buffer
will be contiguous (since they are allocated with kmalloc)
...although maybe I should have the bounce buffers in the driver and allocate
them with devm_get_free_pages instead

would either of this would be acceptable?