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

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Message-ID: <570BF933.2000607@denx.de>
Date:	Mon, 11 Apr 2016 21:21:23 +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 04/11/2016 03:28 AM, Jiancheng Xue wrote:
> Hi,
> 
> On 2016/4/8 18:04, Marek Vasut wrote:
>> 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.
>>
> When read_buf is allocated by vmalloc, the underlying physical memory may be not contiguous.
> In this case, dma_map_single can't be used directly. I think inner DMA buffer and memcpy are still
> needed. Am I right?

Take a look at drivers/spi/spi-mxs.c , look for "vmalloc" , does that
solution help you in any way ?

-- 
Best regards,
Marek Vasut