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Date:   Tue, 10 Apr 2018 11:44:28 +0200
From:   Miquel Raynal <miquel.raynal@bootlin.com>
To:     Abhishek Sahu <absahu@codeaurora.org>
Cc:     Boris Brezillon <boris.brezillon@free-electrons.com>,
        Archit Taneja <architt@codeaurora.org>,
        Richard Weinberger <richard@nod.at>,
        linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org,
        Marek Vasut <marek.vasut@gmail.com>,
        linux-mtd@lists.infradead.org,
        Cyrille Pitchen <cyrille.pitchen@wedev4u.fr>,
        Andy Gross <andy.gross@linaro.org>,
        Brian Norris <computersforpeace@gmail.com>,
        David Woodhouse <dwmw2@infradead.org>
Subject: Re: [PATCH 8/9] mtd: nand: qcom: helper function for raw read
Message-ID: <20180410114428.68d59c8d@xps13>
In-Reply-To: <1522845745-6624-9-git-send-email-absahu@codeaurora.org>
References: <1522845745-6624-1-git-send-email-absahu@codeaurora.org>
        <1522845745-6624-9-git-send-email-absahu@codeaurora.org>
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Hi Abhishek,

On Wed,  4 Apr 2018 18:12:24 +0530, Abhishek Sahu
<absahu@codeaurora.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.

I am not sure this is the right approach for subpage reads. If the
controller supports it, you should just enable it in chip->options.

> 
> Signed-off-by: Abhishek Sahu <absahu@codeaurora.org>
> ---
>  drivers/mtd/nand/qcom_nandc.c | 186 +++++++++++++++++++++++++-----------------
>  1 file changed, 110 insertions(+), 76 deletions(-)
> 
> diff --git a/drivers/mtd/nand/qcom_nandc.c b/drivers/mtd/nand/qcom_nandc.c
> index 40c790e..f5d1fa4 100644
> --- a/drivers/mtd/nand/qcom_nandc.c
> +++ b/drivers/mtd/nand/qcom_nandc.c
> @@ -1590,6 +1590,114 @@ 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 for which the data should be read. The
> + * single page contains multiple CW. Sometime, only few CW data is required
> + * in complete page. Also, 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 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)
> +{
> +	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++) {
> +		int data_size1, data_size2, oob_size1, oob_size2;
> +		int reg_off = FLASH_BUF_ACC;
> +
> +		data_size1 = mtd->writesize - host->cw_size * (ecc->steps - 1);
> +		oob_size1 = host->bbm_size;
> +
> +		if (i == (ecc->steps - 1)) {
> +			data_size2 = ecc->size - data_size1 -
> +				     ((ecc->steps - 1) << 2);
> +			oob_size2 = (ecc->steps << 2) + host->ecc_bytes_hw +
> +				    host->spare_bytes;
> +		} else {
> +			data_size2 = host->cw_data - data_size1;
> +			oob_size2 = host->ecc_bytes_hw + host->spare_bytes;
> +		}
> +
> +		/*
> +		 * Don't perform actual data copy from NAND controller to data
> +		 * buffer through DMA for this codeword
> +		 */
> +		if (!(read_cw_mask & BIT(i))) {
> +			if (nandc->props->is_bam)
> +				nandc_set_read_loc(nandc, 0, 0, 0, 1);
> +
> +			config_nand_cw_read(nandc, false);
> +
> +			data_buf += data_size1 + data_size2;
> +			oob_buf += oob_size1 + oob_size2;
> +
> +			continue;
> +		}
> +
> +		if (nandc->props->is_bam) {
> +			read_loc = 0;
> +			nandc_set_read_loc(nandc, 0, read_loc, data_size1, 0);
> +			read_loc += data_size1;
> +
> +			nandc_set_read_loc(nandc, 1, read_loc, oob_size1, 0);
> +			read_loc += oob_size1;
> +
> +			nandc_set_read_loc(nandc, 2, read_loc, data_size2, 0);
> +			read_loc += data_size2;
> +
> +			nandc_set_read_loc(nandc, 3, read_loc, oob_size2, 1);
> +		}
> +
> +		config_nand_cw_read(nandc, false);
> +
> +		read_data_dma(nandc, reg_off, data_buf, data_size1, 0);
> +		reg_off += data_size1;
> +		data_buf += data_size1;
> +
> +		read_data_dma(nandc, reg_off, oob_buf, oob_size1, 0);
> +		reg_off += oob_size1;
> +		oob_buf += oob_size1;
> +
> +		read_data_dma(nandc, reg_off, data_buf, data_size2, 0);
> +		reg_off += data_size2;
> +		data_buf += data_size2;
> +
> +		read_data_dma(nandc, reg_off, oob_buf, oob_size2, 0);
> +		oob_buf += oob_size2;
> +	}
> +
> +	ret = submit_descs(nandc);
> +	if (ret)
> +		dev_err(nandc->dev, "failure to read raw page\n");
> +
> +	free_descs(nandc);
> +
> +	if (!ret)
> +		ret = check_flash_errors(host, last_step - start_step);
> +
> +	return 0;
> +}
> +
> +/*
>   * reads back status registers set by the controller to notify page read
>   * errors. this is equivalent to what 'ecc->correct()' would do.
>   */
> @@ -1839,82 +1947,8 @@ static int qcom_nandc_read_page_raw(struct mtd_info *mtd,
>  				    struct nand_chip *chip, uint8_t *buf,
>  				    int oob_required, int page)
>  {
> -	struct qcom_nand_host *host = to_qcom_nand_host(chip);
> -	struct qcom_nand_controller *nandc = get_qcom_nand_controller(chip);
> -	u8 *data_buf, *oob_buf;
> -	struct nand_ecc_ctrl *ecc = &chip->ecc;
> -	int i, ret;
> -	int read_loc;
> -
> -	nand_read_page_op(chip, page, 0, NULL, 0);
> -	data_buf = buf;
> -	oob_buf = chip->oob_poi;
> -
> -	host->use_ecc = false;
> -
> -	clear_bam_transaction(nandc);
> -	update_rw_regs(host, ecc->steps, true);
> -	config_nand_page_read(nandc);
> -
> -	for (i = 0; i < ecc->steps; i++) {
> -		int data_size1, data_size2, oob_size1, oob_size2;
> -		int reg_off = FLASH_BUF_ACC;
> -
> -		data_size1 = mtd->writesize - host->cw_size * (ecc->steps - 1);
> -		oob_size1 = host->bbm_size;
> -
> -		if (i == (ecc->steps - 1)) {
> -			data_size2 = ecc->size - data_size1 -
> -				     ((ecc->steps - 1) << 2);
> -			oob_size2 = (ecc->steps << 2) + host->ecc_bytes_hw +
> -				    host->spare_bytes;
> -		} else {
> -			data_size2 = host->cw_data - data_size1;
> -			oob_size2 = host->ecc_bytes_hw + host->spare_bytes;
> -		}
> -
> -		if (nandc->props->is_bam) {
> -			read_loc = 0;
> -			nandc_set_read_loc(nandc, 0, read_loc, data_size1, 0);
> -			read_loc += data_size1;
> -
> -			nandc_set_read_loc(nandc, 1, read_loc, oob_size1, 0);
> -			read_loc += oob_size1;
> -
> -			nandc_set_read_loc(nandc, 2, read_loc, data_size2, 0);
> -			read_loc += data_size2;
> -
> -			nandc_set_read_loc(nandc, 3, read_loc, oob_size2, 1);
> -		}
> -
> -		config_nand_cw_read(nandc, false);
> -
> -		read_data_dma(nandc, reg_off, data_buf, data_size1, 0);
> -		reg_off += data_size1;
> -		data_buf += data_size1;
> -
> -		read_data_dma(nandc, reg_off, oob_buf, oob_size1, 0);
> -		reg_off += oob_size1;
> -		oob_buf += oob_size1;
> -
> -		read_data_dma(nandc, reg_off, data_buf, data_size2, 0);
> -		reg_off += data_size2;
> -		data_buf += data_size2;
> -
> -		read_data_dma(nandc, reg_off, oob_buf, oob_size2, 0);
> -		oob_buf += oob_size2;
> -	}
> -
> -	ret = submit_descs(nandc);
> -	if (ret)
> -		dev_err(nandc->dev, "failure to read raw page\n");
> -
> -	free_descs(nandc);
> -
> -	if (!ret)
> -		ret = check_flash_errors(host, ecc->steps);
> -
> -	return 0;
> +	return nandc_read_page_raw(mtd, chip, buf, chip->oob_poi, page,
> +				   BIT(chip->ecc.steps) - 1);

I don't understand this. chip->ecc.steps is constant, right? So you
always ask for the same subpage?

>  }
>  
>  /* implements ecc->read_oob() */


-- 
Miquel Raynal, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com