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 19:08:27 +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 2018/11/6 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.

>>>
>>> Isn't the controller engine able to wait on the data transfer to be
>>> complete before sending the next instruction in the CMD FIFO pipe?
>>> I'm pretty sure it's able to do that, which would make
>>> meson_nfc_wait_dma_finish() useless, and all you'd have to do is wait
>>> for the CMD FIFO to be empty (assuming it guarantees the last command
>>> has been executed).
>>> Maybe the nfc design is difference. dedicated nfc dma engine is
>> concatenated with the command fifo, there is no other status to check
>> whether dma is done.
> 
> No, I mean that internally a "DMA-transfer" instruction probably
> forces the NAND controller to wait for the DMA transfer to be finished
> before dequeuing/executing the next instruction. So, it should be safe
> to queue the PROG and WAIT_RB instructions and just rely on the "FIFO
> empty" event to consider the operation as finished. Then, all you'll
> have to do is check the status reg to determine whether the
> write operation succeeded or not.
> 
em, i got the point. indeed, until dma is checked done, nfc will execute 
next command in the command queue. so i will consider it.

> .
>