linux-kernel - Re: [PATCH v4 3/5] mtd: rawnand: meson: always read whole OOB bytes

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Message-ID: <ae791be4-1c44-240d-2559-37523b654506@sberdevices.ru>
Date:   Mon, 29 May 2023 22:46:59 +0300
From:   Arseniy Krasnov <avkrasnov@...rdevices.ru>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
CC:     Liang Yang <liang.yang@...ogic.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Kevin Hilman <khilman@...libre.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Jianxin Pan <jianxin.pan@...ogic.com>,
        Yixun Lan <yixun.lan@...ogic.com>, <oxffffaa@...il.com>,
        <kernel@...rdevices.ru>, <linux-mtd@...ts.infradead.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-amlogic@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 3/5] mtd: rawnand: meson: always read whole OOB bytes



On 26.05.2023 20:09, Miquel Raynal wrote:
> Hi Arseniy,
> 
> avkrasnov@...rdevices.ru wrote on Tue, 23 May 2023 20:27:35 +0300:
> 
>> On 22.05.2023 18:38, Miquel Raynal wrote:
>>> Hi Arseniy,
>>>
>>> AVKrasnov@...rdevices.ru wrote on Mon, 15 May 2023 12:44:37 +0300:
>>>   
>>>> This changes size of read access to OOB area by reading all bytes of
>>>> OOB (free bytes + ECC engine bytes).  
>>>
>>> This is normally up to the user (user in your case == jffs2). The
>>> controller driver should expose a number of user accessible bytes and
>>> then when users want the OOB area, they should access it entirely. On
>>> top of that read, they can extract (or "write only") the user bytes.  
>>
>> Sorry, I didn't get it. If driver exposes N bytes of user accessible bytes,
>> I must always return whole OOB yes? E.g. N + rest of OOB
> 
> Yes. At the NAND controller level, you get asked for either a page of
> data (sometimes a subpage, but whatever), and/or the oob area. You need
> to provide what is requested, no more, no less. The upper layers will
> trim down what's uneeded and extract the bytes they want.

I see, so in this case I think this patch could be merged to the patch which
changes OOB layout be moving it out of ECC area? Because driver MUST return all
bytes of OOB area.

> 
>>>> Signed-off-by: Arseniy Krasnov <AVKrasnov@...rdevices.ru>
>>>> ---
>>>>  drivers/mtd/nand/raw/meson_nand.c | 24 ++++++++++++++++++++++++
>>>>  1 file changed, 24 insertions(+)
>>>>
>>>> diff --git a/drivers/mtd/nand/raw/meson_nand.c b/drivers/mtd/nand/raw/meson_nand.c
>>>> index 8526a6b87720..a31106c943d7 100644
>>>> --- a/drivers/mtd/nand/raw/meson_nand.c
>>>> +++ b/drivers/mtd/nand/raw/meson_nand.c
>>>> @@ -755,6 +755,30 @@ static int __meson_nfc_read_oob(struct nand_chip *nand, int page,
>>>>  	u32 oob_bytes;
>>>>  	u32 page_size;
>>>>  	int ret;
>>>> +	int i;
>>>> +
>>>> +	/* Read ECC codes and user bytes. */
>>>> +	for (i = 0; i < nand->ecc.steps; i++) {
>>>> +		u32 ecc_offs = nand->ecc.size * (i + 1) +
>>>> +			       NFC_OOB_PER_ECC(nand) * i;
>>>> +
>>>> +		ret = nand_read_page_op(nand, page, 0, NULL, 0);
>>>> +		if (ret)
>>>> +			return ret;
>>>> +
>>>> +		/* Use temporary buffer, because 'nand_change_read_column_op()'
>>>> +		 * seems work with some alignment, so we can't read data to
>>>> +		 * 'oob_buf' directly.  
>>>
>>> DMA?  
>>
>> Yes I guess, this address passed to exec_op code and used as DMA.
> 
> If your controller uses DMA on exec_op accesses, then yes. Exec_op
> reads/writes are usually small enough (or not time sensitive at all if
> they are bigger) so it's not required to use DMA there. Anyhow, oob_buf
> is suitable for DMA purposes, so I'm a bit surprised you need a bounce
> buffer, if that's the only reason. Maybe you need a bounce buffer to
> reorganize the data. That would be a much better explanation.

Yes! I remove this temporary buffer, seems my mistake! Without it everything works
good, I'll remove it from the next version!

Thanks, Arseniy

> 
>>>> +		 */
>>>> +		ret = nand_change_read_column_op(nand, ecc_offs, meson_chip->oob_buf,
>>>> +						 NFC_OOB_PER_ECC(nand), false);
>>>> +		if (ret)
>>>> +			return ret;
>>>> +
>>>> +		memcpy(oob_buf + i * NFC_OOB_PER_ECC(nand),
>>>> +		       meson_chip->oob_buf,
>>>> +		       NFC_OOB_PER_ECC(nand));
>>>> +	}
>>>>  
>>>>  	oob_bytes = meson_nfc_get_oob_bytes(nand);
>>>>    
>>>
>>>
>>> Thanks,
>>> Miquèl  
>>
>> Thanks, Arseniy
> 
> 
> Thanks,
> Miquèl