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SubjectRe: [PATCH v4 04/23] mtd: nand: denali: avoid hard-coding ECC step, strength, bytes
On Tue,  6 Jun 2017 08:21:43 +0900
Masahiro Yamada <yamada.masahiro@socionext.com> wrote:

> This driver was originally written for the Intel MRST platform with
> several platform-specific parameters hard-coded.
>
> Currently, the ECC settings are hard-coded as follows:
>
> #define ECC_SECTOR_SIZE 512
> #define ECC_8BITS 14
> #define ECC_15BITS 26
>
> Therefore, the driver can only support two cases.
> - ecc.size = 512, ecc.strength = 8 --> ecc.bytes = 14
> - ecc.size = 512, ecc.strength = 15 --> ecc.bytes = 26
>
> However, these are actually customizable parameters, for example,
> UniPhier platform supports the following:
>
> - ecc.size = 1024, ecc.strength = 8 --> ecc.bytes = 14
> - ecc.size = 1024, ecc.strength = 16 --> ecc.bytes = 28
> - ecc.size = 1024, ecc.strength = 24 --> ecc.bytes = 42
>
> So, we need to handle the ECC parameters in a more generic manner.
> Fortunately, the Denali User's Guide explains how to calculate the
> ecc.bytes. The formula is:
>
> ecc.bytes = 2 * CEIL(13 * ecc.strength / 16) (for ecc.size = 512)
> ecc.bytes = 2 * CEIL(14 * ecc.strength / 16) (for ecc.size = 1024)
>
> For DT platforms, it would be reasonable to allow DT to specify ECC
> strength by either "nand-ecc-strength" or "nand-ecc-maximize". If
> none of them is specified, the driver will try to meet the chip's ECC
> requirement.
>
> For PCI platforms, the max ECC strength is used to keep the original
> behavior.
>
> Newer versions of this IP need ecc.size and ecc.steps explicitly
> set up via the following registers:
> CFG_DATA_BLOCK_SIZE (0x6b0)
> CFG_LAST_DATA_BLOCK_SIZE (0x6c0)
> CFG_NUM_DATA_BLOCKS (0x6d0)
>
> For older IP versions, write accesses to these registers are just
> ignored.
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> Acked-by: Rob Herring <robh@kernel.org>
> ---
>
> Changes in v4:
> - Rewrite by using generic helpers, nand_check_caps(),
> nand_match_ecc_req(), nand_maximize_ecc().
>
> Changes in v3:
> - Move DENALI_CAP_ define out of struct denali_nand_info
> - Use chip->ecc_step_ds as a hint to choose chip->ecc.size
> where possible
>
> Changes in v2:
> - Change the capability prefix DENALI_CAPS_ -> DENALI_CAP_
> - Make ECC 512 cap and ECC 1024 cap independent
> - Set up three CFG_... registers
>
> .../devicetree/bindings/mtd/denali-nand.txt | 7 ++
> drivers/mtd/nand/denali.c | 103 ++++++++++++++-------
> drivers/mtd/nand/denali.h | 11 ++-
> drivers/mtd/nand/denali_dt.c | 8 ++
> drivers/mtd/nand/denali_pci.c | 9 ++
> 5 files changed, 101 insertions(+), 37 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/mtd/denali-nand.txt b/Documentation/devicetree/bindings/mtd/denali-nand.txt
> index e593bbe..b7742a7 100644
> --- a/Documentation/devicetree/bindings/mtd/denali-nand.txt
> +++ b/Documentation/devicetree/bindings/mtd/denali-nand.txt
> @@ -7,6 +7,13 @@ Required properties:
> - reg-names: Should contain the reg names "nand_data" and "denali_reg"
> - interrupts : The interrupt number.
>
> +Optional properties:
> + - nand-ecc-step-size: see nand.txt for details. If present, the value must be
> + 512 for "altr,socfpga-denali-nand"
> + - nand-ecc-strength: see nand.txt for details. Valid values are:
> + 8, 15 for "altr,socfpga-denali-nand"
> + - nand-ecc-maximize: see nand.txt for details
> +
> The device tree may optionally contain sub-nodes describing partitions of the
> address space. See partition.txt for more detail.
>
> diff --git a/drivers/mtd/nand/denali.c b/drivers/mtd/nand/denali.c
> index 16634df..3204c51 100644
> --- a/drivers/mtd/nand/denali.c
> +++ b/drivers/mtd/nand/denali.c
> @@ -886,8 +886,6 @@ static int denali_hw_ecc_fixup(struct mtd_info *mtd,
> return max_bitflips;
> }
>
> -#define ECC_SECTOR_SIZE 512
> -
> #define ECC_SECTOR(x) (((x) & ECC_ERROR_ADDRESS__SECTOR_NR) >> 12)
> #define ECC_BYTE(x) (((x) & ECC_ERROR_ADDRESS__OFFSET))
> #define ECC_CORRECTION_VALUE(x) ((x) & ERR_CORRECTION_INFO__BYTEMASK)
> @@ -899,6 +897,7 @@ static int denali_sw_ecc_fixup(struct mtd_info *mtd,
> struct denali_nand_info *denali,
> unsigned long *uncor_ecc_flags, uint8_t *buf)
> {
> + unsigned int ecc_size = denali->nand.ecc.size;
> unsigned int bitflips = 0;
> unsigned int max_bitflips = 0;
> uint32_t err_addr, err_cor_info;
> @@ -928,9 +927,9 @@ static int denali_sw_ecc_fixup(struct mtd_info *mtd,
> * an erased sector.
> */
> *uncor_ecc_flags |= BIT(err_sector);
> - } else if (err_byte < ECC_SECTOR_SIZE) {
> + } else if (err_byte < ecc_size) {
> /*
> - * If err_byte is larger than ECC_SECTOR_SIZE, means error
> + * If err_byte is larger than ecc_size, means error
> * happened in OOB, so we ignore it. It's no need for
> * us to correct it err_device is represented the NAND
> * error bits are happened in if there are more than
> @@ -939,7 +938,7 @@ static int denali_sw_ecc_fixup(struct mtd_info *mtd,
> int offset;
> unsigned int flips_in_byte;
>
> - offset = (err_sector * ECC_SECTOR_SIZE + err_byte) *
> + offset = (err_sector * ecc_size + err_byte) *
> denali->devnum + err_device;
>
> /* correct the ECC error */
> @@ -1345,13 +1344,55 @@ static void denali_hw_init(struct denali_nand_info *denali)
> denali_irq_init(denali);
> }
>
> -/*
> - * Althogh controller spec said SLC ECC is forceb to be 4bit,
> - * but denali controller in MRST only support 15bit and 8bit ECC
> - * correction
> - */
> -#define ECC_8BITS 14
> -#define ECC_15BITS 26
> +static int denali_calc_ecc_bytes(int step_size, int strength)
> +{
> + int coef;
> +
> + switch (step_size) {
> + case 512:
> + coef = 13;
> + break;
> + case 1024:
> + coef = 14;
> + break;
> + default:
> + return -ENOTSUPP;
> + }
> +
> + return DIV_ROUND_UP(strength * coef, 16) * 2;

or just

return DIV_ROUND_UP(strength * fls(8 * step_size), 16) * 2;

the array of supported step size/strength should guarantee that you're
called with unsupported settings.

> +}
> +
> +static int denali_ecc_setup(struct mtd_info *mtd, struct nand_chip *chip,
> + struct denali_nand_info *denali)
> +{
> + struct nand_ecc_caps caps;
> + int ret;
> +
> + caps.stepinfos = denali->stepinfo;
> + caps.nstepinfos = 1;
> + caps.calc_ecc_bytes = denali_calc_ecc_bytes;
> + caps.oob_reserve_bytes = denali->bbtskipbytes;

If you get rid of this oob_reserve_bytes field, you can define caps as
a static const and even directly store ecc_caps in denali_nand_info.

> +
> + /*
> + * If .size and .strength are already set (usually by DT),
> + * check if they are supported by this controller.
> + */
> + if (chip->ecc.size && chip->ecc.strength)
> + return nand_check_ecc_caps(mtd, chip, &caps);
> +
> + /*
> + * We want .size and .strength closest to the chip's requirement
> + * unless NAND_ECC_MAXIMIZE is requested.
> + */
> + if (!(chip->ecc.options & NAND_ECC_MAXIMIZE)) {
> + ret = nand_match_ecc_req(mtd, chip, &caps);
> + if (!ret)
> + return 0;
> + }
> +
> + /* Max ECC strength is the last thing we can do */
> + return nand_maximize_ecc(mtd, chip, &caps);
> +}

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