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

From: Boris Brezillon
Date: Tue Apr 12 2016 - 05:44:41 EST


+Russell

Hi Jiancheng,

On Tue, 12 Apr 2016 17:32:08 +0800
Jiancheng Xue <xuejiancheng@xxxxxxxxxx> 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