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

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Message-ID: <7afe4622-7233-3266-51dd-a764458e5d34@amlogic.com>
Date:   Thu, 8 Nov 2018 15:41:53 +0800
From:   Liang Yang <liang.yang@...ogic.com>
To:     Boris Brezillon <boris.brezillon@...tlin.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 2018/11/7 0:16, Boris Brezillon wrote:
> 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.
> 

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?

> .
>