Re: [PATCH v6 2/2] mtd: rawnand: meson: add support for Amlogic NAND flash controller

[Liang Yang]

On 2018/11/7 0:16, Boris Brezillon wrote:
> On Tue, 6 Nov 2018 19:08:27 +0800
> Liang Yang <liang.yang@xxxxxxxxxxx> wrote:
>
> > On 2018/11/6 18:22, Boris Brezillon wrote:
> > > On Tue, 6 Nov 2018 18:00:37 +0800
> > > Liang Yang <liang.yang@xxxxxxxxxxx> wrote:
> > >    
> > > > On 2018/11/6 17:28, Boris Brezillon wrote:
> > > > > On Tue, 6 Nov 2018 17:08:00 +0800
> > > > > Liang Yang <liang.yang@xxxxxxxxxxx> wrote:
> > > > >       
> > > > > > On 2018/11/5 23:53, Boris Brezillon wrote:
> > > > > > > On Fri, 2 Nov 2018 00:42:21 +0800
> > > > > > > Jianxin Pan <jianxin.pan@xxxxxxxxxxx> wrote:
> > > > > > >          
> > > > > > > > +
> > > > > > > > +static inline u8 meson_nfc_read_byte(struct mtd_info *mtd)
> > > > > > > > +{
> > > > > > > > +	struct nand_chip *nand = mtd_to_nand(mtd);
> > > > > > > > +	struct meson_nfc *nfc = nand_get_controller_data(nand);
> > > > > > > > +	u32 cmd;
> > > > > > > > +
> > > > > > > > +	cmd = nfc->param.chip_select | NFC_CMD_DRD | 0;
> > > > > > > > +	writel(cmd, nfc->reg_base + NFC_REG_CMD);
> > > > > > > > +
> > > > > > > > +	meson_nfc_drain_cmd(nfc);
> > > > > > >
> > > > > > > You probably don't want to drain the FIFO every time you read a byte on
> > > > > > > the bus, and I guess the INPUT FIFO is at least as big as the CMD
> > > > > > > FIFO, right? If that's the case, you should queue as much DRD cmd as
> > > > > > > possible and only sync when the user explicitly requests it or when
> > > > > > > the INPUT/READ FIFO is full.
> > > > > > >          
> > > > > > Register 'NFC_REG_BUF' can holds only 4 bytes, also DRD sends only one
> > > > > > nand cycle to read one byte and covers the 1st byte every time reading.
> > > > > > i think nfc controller is faster than nand cycle, but really it is not
> > > > > > high efficiency when reading so many bytes once.
> > > > > > Or use dma command here like read_page and read_page_raw.
> > > > >
> > > > > Yep, that's also an alternative, though you'll have to make sure the
> > > > > buffer passed through the nand_op_inst is DMA-safe, and use a bounce
> > > > > buffer when that's not the case.
> > > > >       
> > > > ok, i will try dma here.
> > >
> > > We should probably expose the bounce buf handling as generic helpers at
> > > the rawnand level:
> > >
> > > void *nand_op_get_dma_safe_input_buf(struct nand_op_instr *instr)
> > > {
> > > 	void *buf;
> > >
> > > 	if (WARN_ON(instr->type != NAND_OP_DATA_IN_INSTR))
> > > 		return NULL;
> > >
> > > 	if (virt_addr_valid(instr->data.in) &&
> > > 	    !object_is_on_stack(instr->data.buf.in))
> > > 		return instr->data.buf.in;
> > >
> > > 	return kzalloc(instr->data.len, GFP_KERNEL);
> > > }
> > >
> > > void nand_op_put_dma_safe_input_buf(struct nand_op_instr *instr,
> > > 				    void *buf)
> > > {
> > > 	if (WARN_ON(instr->type != NAND_OP_DATA_IN_INSTR) ||
> > > 	    WARN_ON(!buf))
> > > 		return;
> > >
> > > 	if (buf == instr->data.buf.in)
> > > 		return;
> > >
> > > 	memcpy(instr->data.buf.in, buf, instr->data.len);
> > > 	kfree(buf);
> > > }
> > >
> > > const void *nand_op_get_dma_safe_output_buf(struct nand_op_instr *instr)
> > > {
> > > 	void *buf;
> > >
> > > 	if (WARN_ON(instr->type != NAND_OP_DATA_OUT_INSTR))
> > > 		return NULL;
> > >
> > > 	if (virt_addr_valid(instr->data.out) &&
> > > 	    !object_is_on_stack(instr->data.buf.out))
> > > 		return instr->data.buf.out;
> > >
> > > 	return kmemdup(instr->data.buf.out, GFP_KERNEL);
> > > }
> > >
> > > void nand_op_put_dma_safe_output_buf(struct nand_op_instr *instr,
> > > 				    void *buf)
> > > {
> > > 	if (WARN_ON(instr->type != NAND_OP_DATA_OUT_INSTR) ||
> > > 	    WARN_ON(!buf))
> > > 		return;
> > >
> > > 	if (buf != instr->data.buf.out)
> > > 		kfree(buf);
> > > }
> > >   
> >
> > that is more convenient.
> > i will use meson_chip->databuf as the bounce mid-buffer now.
>
> It won't work: the bounce buffer is allocated after the detection, and
> the detection code is calling ->exec_op().
>
> Just add a new patch to you series adding these helpers to nand_base.c.

when using these helpers, i finally find that i still need a *info 
buffer* which is used to get status and ecc counter. even i don't need
to check *info buffer*, it is still needed. i just malloc *info_buffer* 
in driver now. and then i think some dedicated dma may need a minimum 
size(such as 4 bytes). it is luckly that meson nfc is not limited about 
the minimum size and i tested it.
so what is your suggestion about it?

> .