linux-kernel - Re: [RESEND PATCH v9] mtd: spi-nor: add hisilicon spi-nor flash controller driver

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Date:	Fri, 08 Apr 2016 12:04:15 +0200
From:	Marek Vasut <marex@...x.de>
To:	Jiancheng Xue <xuejiancheng@...wei.com>,
	Brian Norris <computersforpeace@...il.com>
CC:	linux-mtd@...ts.infradead.org, robh+dt@...nel.org,
	dwmw2@...radead.org, boris.brezillon@...e-electrons.com,
	juhosg@...nwrt.org, furquan@...gle.com, suwenping@...ilicon.com,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	yanhaifeng@...ilicon.com, raojun@...ilicon.com,
	xuejiancheng@...ilicon.com, ml.yang@...ilicon.com,
	gaofei@...ilicon.com, yanghongwei@...ilicon.com,
	zhangzhenxing@...ilicon.com
Subject: Re: [RESEND PATCH v9] mtd: spi-nor: add hisilicon spi-nor flash controller
 driver

On 04/08/2016 10:26 AM, Jiancheng Xue wrote:
> Hi,
> 
> On 2016/4/7 10:28, Marek Vasut wrote:
>> On 04/07/2016 04:10 AM, Jiancheng Xue wrote:
>>> Hi Brian,
>>>    Thank you very much for your comments. I'll fix these issues in next version.
>>> In addition, for easy understanding I'd like to rewrite hisi_spi_nor_write and
>>> hisi_spi_nor_read. Your comments on these modifications will be highly appreciated.
>>
>> Would you please stop top-posting ? It rubs some people the wrong way.
>>
> I feel very sorry about that. I have read the etiquette and won't make the same mistake again.
> 
>>> static int hisi_spi_nor_read(struct spi_nor *nor, loff_t from, size_t len,
>>> 		size_t *retlen, u_char *read_buf)
>>> {
>>> 	struct hifmc_priv *priv = nor->priv;
>>> 	struct hifmc_host *host = priv->host;
>>> 	int i;
>>>
>>> 	/* read all bytes in only one time */
>>> 	if (len <= HIFMC_DMA_MAX_LEN) {
>>> 		hisi_spi_nor_dma_transfer(nor, from, host->dma_buffer,
>>> 				len, FMC_OP_READ);
>>> 		memcpy(read_buf, host->buffer, len);
>>
>> Is all the ad-hoc memcpying necessary? I think you can use
>> dma_map_single() and co to obtain DMAble memory for your
>> controller's use and then you can probably get rid of most
>> of this stuff.
>>
> Considering read_buf >= high_mem case, I think it is also complicated to use dma_map_*
> and the DMA buffer allocated by the driver is still needed. But I am not sure about
> this. Please let me know if I am wrong. Thank you!

Does your controller/DMA have a limitation where it's buffers must be in
the bottom 4GiB range ? The DMA framework should be able to take care of
such platform limitations.

Best regards,
Marek Vasut