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

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Date:	Tue, 12 Apr 2016 17:32:08 +0800
From:	Jiancheng Xue <xuejiancheng@...wei.com>
To:	Marek Vasut <marex@...x.de>,
	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>,
	<jalen.hsu@...ilicon.com>
Subject: Re: [RESEND PATCH v9] mtd: spi-nor: add hisilicon spi-nor flash
 controller driver

Hi Marek,

On 2016/4/12 3:21, Marek Vasut wrote:
> 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 ?
> 
No. I think this solution just processes the buffer within only one page.
I had referred to drivers/mtd/onenand/samsung.c and other files.
The corresponding code segment is as follows:
static int s5pc110_read_bufferram(struct mtd_info *mtd, int area,
                unsigned char *buffer, int offset, size_t count)
{
	void *buf = (void *) buffer;
        dma_addr_t dma_src, dma_dst;
	...
	/* Handle vmalloc address */
        if (buf >= high_memory) {
                struct page *page;

                if (((size_t) buf & PAGE_MASK) !=
                    ((size_t) (buf + count - 1) & PAGE_MASK))
                        goto normal;
                page = vmalloc_to_page(buf);
                if (!page)
                        goto normal;

                ...
        } else {
		...
	}

normal:
        ...
        memcpy(buffer, p, count);

	return 0;
}
I think memcpy in "normal" clause can't be removed. So I'd like to keep my original
implementation if it is also OK. What's your opinion?

Regards,
Jiancheng