linux-kernel - Re: [PATCH v3 15/16] mtd: rawnand: qcom: helper function for raw read

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Date:   Sun, 27 May 2018 15:53:11 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Abhishek Sahu <absahu@...eaurora.org>
Cc:     Boris Brezillon <boris.brezillon@...tlin.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mtd@...ts.infradead.org, Andy Gross <andy.gross@...aro.org>,
        Archit Taneja <architt@...eaurora.org>
Subject: Re: [PATCH v3 15/16] mtd: rawnand: qcom: helper function for raw
 read

Hi Abhishek,

On Fri, 25 May 2018 17:51:43 +0530, Abhishek Sahu
<absahu@...eaurora.org> wrote:

> This patch does minor code reorganization for raw reads.
> Currently the raw read is required for complete page but for
> subsequent patches related with erased codeword bit flips
> detection, only few CW should be read. So, this patch adds
> helper function and introduces the read CW bitmask which
> specifies which CW reads are required in complete page.
> 
> Signed-off-by: Abhishek Sahu <absahu@...eaurora.org>
> ---
> * Changes from v2:
>   NONE
> 
> * Changes from v1:
>  1. Included more detail in function comment
> 
>  drivers/mtd/nand/raw/qcom_nandc.c | 197 ++++++++++++++++++++++++--------------
>  1 file changed, 123 insertions(+), 74 deletions(-)
> 
> diff --git a/drivers/mtd/nand/raw/qcom_nandc.c b/drivers/mtd/nand/raw/qcom_nandc.c
> index 87f900e..34143a4 100644
> --- a/drivers/mtd/nand/raw/qcom_nandc.c
> +++ b/drivers/mtd/nand/raw/qcom_nandc.c
> @@ -1588,6 +1588,127 @@ static int check_flash_errors(struct qcom_nand_host *host, int cw_cnt)
>  }
>  
>  /*
> + * Helper to perform the page raw read operation. The read_cw_mask will be
> + * used to specify the codewords (CW) for which the data should be read. The
> + * single page contains multiple CW.
> + *
> + * Normally other NAND controllers store the data in main area and
> + * ecc bytes in OOB area. So, if page size is 2048+64 then 2048
> + * data bytes will go in main area followed by ECC bytes. The QCOM NAND
> + * controller follows different layout in which the data+OOB is internally
> + * divided in 528/532 bytes CW and each CW contains 516 bytes followed by
> + * ECC parity bytes for that CW. By this, 4 available OOB bytes per CW
> + * will also be protected with ECC.
> + *
> + * For each CW read, following are the 2 steps:
> + * 1. Read the codeword bytes from NAND chip to NAND controller internal HW
> + *    buffer.
> + * 2. Copy all these bytes from this HW buffer to actual buffer.
> + *
> + * Sometime, only few CW data is required in complete page. The read_cw_mask
> + * specifies which CW in a page needs to be read. Start address will be
> + * determined with this CW mask to skip unnecessary data copy from NAND
> + * flash device. Then, actual data copy from NAND controller HW internal buffer
> + * to data buffer will be done only for the CWs, which have the mask set.
> + */
> +static int
> +nandc_read_page_raw(struct mtd_info *mtd, struct nand_chip *chip,
> +		    u8 *data_buf, u8 *oob_buf,
> +		    int page, unsigned long read_cw_mask)

Please prefix the helper with "qcom_nandc"

> +{
> +	struct qcom_nand_host *host = to_qcom_nand_host(chip);
> +	struct qcom_nand_controller *nandc = get_qcom_nand_controller(chip);
> +	struct nand_ecc_ctrl *ecc = &chip->ecc;
> +	int i, ret;
> +	int read_loc, start_step, last_step;
> +
> +	nand_read_page_op(chip, page, 0, NULL, 0);
> +
> +	host->use_ecc = false;
> +	start_step = ffs(read_cw_mask) - 1;
> +	last_step = fls(read_cw_mask);
> +
> +	clear_bam_transaction(nandc);
> +	set_address(host, host->cw_size * start_step, page);
> +	update_rw_regs(host, last_step - start_step, true);
> +	config_nand_page_read(nandc);
> +
> +	for (i = start_step; i < last_step; i++) {

This comment applies for both patches 15 and 16:

I would really prefer having a qcom_nandc_read_cw_raw() that reads only
one CW. From qcom_nandc_read_page_raw() you would loop over all the CW
calling qcom_nandc_read_cw_raw() helper (it's raw reads, we don't care
about performances) and from ->read_page_raw() you would check
CW with uncorrectable errors for being blank with that helper. You
would avoid the not-so-nice logic where you read all the CW between the
first bad one and the last bad one.

Thanks,
Miquèl