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

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Date:   Tue, 6 Nov 2018 17:16:55 +0100
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Liang Yang <liang.yang@...ogic.com>
Cc:     Jianxin Pan <jianxin.pan@...ogic.com>,
        <linux-mtd@...ts.infradead.org>, Yixun Lan <yixun.lan@...ogic.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        Jerome Brunet <jbrunet@...libre.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Carlo Caione <carlo@...one.org>,
        Kevin Hilman <khilman@...libre.com>,
        Rob Herring <robh@...nel.org>, Jian Hu <jian.hu@...ogic.com>,
        Hanjie Lin <hanjie.lin@...ogic.com>,
        Victor Wan <victor.wan@...ogic.com>,
        <linux-amlogic@...ts.infradead.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 2/2] mtd: rawnand: meson: add support for Amlogic
 NAND flash controller

On Tue, 6 Nov 2018 19:08:27 +0800
Liang Yang <liang.yang@...ogic.com> wrote:

> On 2018/11/6 18:22, Boris Brezillon wrote:
> > On Tue, 6 Nov 2018 18:00:37 +0800
> > Liang Yang <liang.yang@...ogic.com> wrote:
> >   
> >> On 2018/11/6 17:28, Boris Brezillon wrote:  
> >>> On Tue, 6 Nov 2018 17:08:00 +0800
> >>> Liang Yang <liang.yang@...ogic.com> wrote:
> >>>      
> >>>> On 2018/11/5 23:53, Boris Brezillon wrote:  
> >>>>> On Fri, 2 Nov 2018 00:42:21 +0800
> >>>>> Jianxin Pan <jianxin.pan@...ogic.com> 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.