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 11:44:33 +0200
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	Jiancheng Xue <xuejiancheng@...wei.com>
Cc:	Marek Vasut <marex@...x.de>,
	Brian Norris <computersforpeace@...il.com>,
	<linux-mtd@...ts.infradead.org>, <robh+dt@...nel.org>,
	<dwmw2@...radead.org>, <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>,
	Russell King - ARM Linux <linux@....linux.org.uk>
Subject: Re: [RESEND PATCH v9] mtd: spi-nor: add hisilicon spi-nor flash
 controller driver

+Russell

Hi Jiancheng,

On Tue, 12 Apr 2016 17:32:08 +0800
Jiancheng Xue <xuejiancheng@...wei.com> wrote:

> 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?

You might want to have a look at this series [1], and particularly at
Russell's answers regarding DMA operations on non-lowmem memory.

Best Regards,

Boris

[1]http://thread.gmane.org/gmane.linux.kernel.mm/149015

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com