linux-kernel - Re: [PATCH v2 02/10] mtd: rawnand: denali: refactor syndrome layout handling for raw access

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Date:   Mon, 4 Mar 2019 10:01:06 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     linux-mtd@...ts.infradead.org,
        Boris Brezillon <bbrezillon@...nel.org>,
        Brian Norris <computersforpeace@...il.com>,
        linux-kernel@...r.kernel.org, Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH v2 02/10] mtd: rawnand: denali: refactor syndrome layout
 handling for raw access

Hi Masahiro,

Masahiro Yamada <yamada.masahiro@...ionext.com> wrote on Tue, 12 Feb
2019 16:12:54 +0900:

> The Denali IP adopts the syndrome page layout (payload and ECC are
> interleaved). The *_page_raw() and *_oob() callbacks are complicated
> because they must hide the underlying layout used by the hardware,
> and always return contiguous in-band and out-of-band data.
> 
> Currently, similar code is duplicated to reorganize the data layout.
> For example, denali_read_page_raw() and denali_write_page_raw() look
> almost the same.
> 
> The idea for refactoring is to split the code into two parts:
>   [1] conversion of page layout
>   [2] what to do at every ECC chunk boundary
> 
> For [1], I wrote denali_raw_payload_op() and denali_raw_oob_op().
> They manipulate data for the Denali controller's specific page layout
> of in-band, out-of-band, respectively.

Could you please comment the purpose of these two functions in the code
as well?

> 
> The difference between write and read is just the operation at
> ECC chunk boundaries. For example, denali_read_oob() calls
> nand_change_read_column_op(), whereas denali_write_oob() calls
> nand_change_write_column_op(). So, I implemented [2] as a callback
> passed into [1].
> 
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> ---
> 
> Changes in v2: None
> 
> drivers/mtd/nand/raw/denali.c | 354 +++++++++++++++++++-----------------------
> 1 file changed, 163 insertions(+), 191 deletions(-)

Too bad that the size of the driver did not shrink more than that :)

[...]

> -	/* OOB free */
> -	len = oobsize - (bufpoi - chip->oob_poi);
> -	if (write)
> -		nand_change_write_column_op(chip, size - len, bufpoi, len,
> -					    false);
> -	else
> -		nand_change_read_column_op(chip, size - len, bufpoi, len,
> -					   false);
> +	return 0;
> +}
> +
> +static int denali_memcpy_in(void *buf, unsigned int offset, unsigned int len,
> +			    void *priv)
> +{
> +	memcpy(buf, priv + offset, len);
> +	return 0;
>  }

Maybe this "callback" and the (_out cousin) could be part of you
controller's structure, and you could use a read/write flag instead of
passing the functions' pointer?


Thanks,
Miquèl