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    SubjectRe: [PATCH 7/9] mtd: nand: qcom: check for operation errors in case of raw read
    Hi Abhishek,

    On Wed, 4 Apr 2018 18:12:23 +0530, Abhishek Sahu
    <absahu@codeaurora.org> wrote:

    > Currently there is no error checking for raw read. For raw
    > reads, there won’t be any ECC failure but the operational
    > failures are possible so schedule the NAND_FLASH_STATUS read
    > after each codeword.
    >
    > Signed-off-by: Abhishek Sahu <absahu@codeaurora.org>
    > ---
    > drivers/mtd/nand/qcom_nandc.c | 56 +++++++++++++++++++++++++++++++++++--------
    > 1 file changed, 46 insertions(+), 10 deletions(-)
    >
    > diff --git a/drivers/mtd/nand/qcom_nandc.c b/drivers/mtd/nand/qcom_nandc.c
    > index dce97e8..40c790e 100644
    > --- a/drivers/mtd/nand/qcom_nandc.c
    > +++ b/drivers/mtd/nand/qcom_nandc.c
    > @@ -1099,7 +1099,8 @@ static void config_nand_page_read(struct qcom_nand_controller *nandc)
    > * Helper to prepare DMA descriptors for configuring registers
    > * before reading each codeword in NAND page.
    > */
    > -static void config_nand_cw_read(struct qcom_nand_controller *nandc)
    > +static void
    > +config_nand_cw_read(struct qcom_nand_controller *nandc, bool use_ecc)
    > {
    > if (nandc->props->is_bam)
    > write_reg_dma(nandc, NAND_READ_LOCATION_0, 4,
    > @@ -1108,19 +1109,25 @@ static void config_nand_cw_read(struct qcom_nand_controller *nandc)
    > write_reg_dma(nandc, NAND_FLASH_CMD, 1, NAND_BAM_NEXT_SGL);
    > write_reg_dma(nandc, NAND_EXEC_CMD, 1, NAND_BAM_NEXT_SGL);
    >
    > - read_reg_dma(nandc, NAND_FLASH_STATUS, 2, 0);
    > - read_reg_dma(nandc, NAND_ERASED_CW_DETECT_STATUS, 1,
    > - NAND_BAM_NEXT_SGL);
    > + if (use_ecc) {
    > + read_reg_dma(nandc, NAND_FLASH_STATUS, 2, 0);
    > + read_reg_dma(nandc, NAND_ERASED_CW_DETECT_STATUS, 1,
    > + NAND_BAM_NEXT_SGL);
    > + } else {
    > + read_reg_dma(nandc, NAND_FLASH_STATUS, 1, NAND_BAM_NEXT_SGL);
    > + }
    > }
    >
    > /*
    > * Helper to prepare dma descriptors to configure registers needed for reading a
    > * single codeword in page
    > */
    > -static void config_nand_single_cw_page_read(struct qcom_nand_controller *nandc)
    > +static void
    > +config_nand_single_cw_page_read(struct qcom_nand_controller *nandc,
    > + bool use_ecc)
    > {
    > config_nand_page_read(nandc);
    > - config_nand_cw_read(nandc);
    > + config_nand_cw_read(nandc, use_ecc);
    > }
    >
    > /*
    > @@ -1201,7 +1208,7 @@ static int nandc_param(struct qcom_nand_host *host)
    > nandc->buf_count = 512;
    > memset(nandc->data_buffer, 0xff, nandc->buf_count);
    >
    > - config_nand_single_cw_page_read(nandc);
    > + config_nand_single_cw_page_read(nandc, false);
    >
    > read_data_dma(nandc, FLASH_BUF_ACC, nandc->data_buffer,
    > nandc->buf_count, 0);
    > @@ -1565,6 +1572,23 @@ struct read_stats {
    > __le32 erased_cw;
    > };
    >
    > +/* reads back FLASH_STATUS register set by the controller */
    > +static int check_flash_errors(struct qcom_nand_host *host, int cw_cnt)
    > +{
    > + struct nand_chip *chip = &host->chip;
    > + struct qcom_nand_controller *nandc = get_qcom_nand_controller(chip);
    > + int i;
    > +
    > + for (i = 0; i < cw_cnt; i++) {
    > + u32 flash = le32_to_cpu(nandc->reg_read_buf[i]);
    > +
    > + if (flash & (FS_OP_ERR | FS_MPU_ERR))
    > + return -EIO;

    This is already checked in parse_read_error(), maybe it would be
    preferable to have different path inside this function depending on the
    'raw' nature of the operation?

    > + }
    > +
    > + return 0;
    > +}
    > +
    > /*
    > * reads back status registers set by the controller to notify page read
    > * errors. this is equivalent to what 'ecc->correct()' would do.
    > @@ -1707,7 +1731,7 @@ static int read_page_ecc(struct qcom_nand_host *host, u8 *data_buf,
    > }
    > }
    >
    > - config_nand_cw_read(nandc);
    > + config_nand_cw_read(nandc, true);
    >
    > if (data_buf)
    > read_data_dma(nandc, FLASH_BUF_ACC, data_buf,
    > @@ -1771,7 +1795,7 @@ static int copy_last_cw(struct qcom_nand_host *host, int page)
    > set_address(host, host->cw_size * (ecc->steps - 1), page);
    > update_rw_regs(host, 1, true);
    >
    > - config_nand_single_cw_page_read(nandc);
    > + config_nand_single_cw_page_read(nandc, host->use_ecc);
    >
    > read_data_dma(nandc, FLASH_BUF_ACC, nandc->data_buffer, size, 0);
    >
    > @@ -1781,6 +1805,15 @@ static int copy_last_cw(struct qcom_nand_host *host, int page)
    >
    > free_descs(nandc);
    >
    > + if (!ret) {
    > + if (host->use_ecc)
    > + ret = parse_read_errors(host, nandc->data_buffer,
    > + nandc->data_buffer + size,
    > + true);
    > + else
    > + ret = check_flash_errors(host, 1);

    This way you would avoid this ^

    > + }
    > +

    As a general way, I don't like very much this kind of error checking
    structure:

    if (!ret)
    ret = something();
    ...
    return ret;

    I would rather prefer:

    if (ret)
    return ret;

    return something();

    > return ret;
    > }
    >
    > @@ -1854,7 +1887,7 @@ static int qcom_nandc_read_page_raw(struct mtd_info *mtd,
    > nandc_set_read_loc(nandc, 3, read_loc, oob_size2, 1);
    > }
    >
    > - config_nand_cw_read(nandc);
    > + config_nand_cw_read(nandc, false);
    >
    > read_data_dma(nandc, reg_off, data_buf, data_size1, 0);
    > reg_off += data_size1;
    > @@ -1878,6 +1911,9 @@ static int qcom_nandc_read_page_raw(struct mtd_info *mtd,
    >
    > free_descs(nandc);
    >
    > + if (!ret)
    > + ret = check_flash_errors(host, ecc->steps);
    > +

    There is not point in doing ret = ... if you return 0 right after.
    Please check what would be the most appropriate.

    > return 0;
    > }
    >

    Thanks,
    Miquèl

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