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SubjectRe: [PATCH v2] mtd: nand: support for Toshiba BENAND (Built-in ECC NAND)
> Please see my patches how to deal with that. Maybe you can find a better solution.

Thank you for your suggestion. I considered to use your submitted patch on BENAND
driver, but I believe reading twice the same page approach will affect read performance.
Additionally, BENAND does not support Disable ECC. So, I cannot use same approach.

I consider other solutions.

BENAND Read Status CMD (70h) can report Rewrite Recommend. BENAND also has extended
ECC Status CMD (7Ah). This can report number of bit error / sector data.
If I can use an extended ECC Status CMD (7Ah) in BENAND driver (nand_benand.c),
I suggest to implement it as the follows:

+++ b/drivers/mtd/nand/nand_benand.c
.....

+/* ECC Status Read Command */
+#define NAND_CMD_ECC_STATUS 0x7A
.....
+ chip->ecc.strength = 8;
.....
+ /* correctable */
+ else if (status & NAND_STATUS_RECOM_REWRT) {
+ if (chip->cmd_ctrl &&
+ IS_ENABLED(CONFIG_MTD_NAND_BENAND_ECC_STATUS)) {
+
+ /* Check Read ECC Status */
+ chip->cmd_ctrl(mtd, NAND_CMD_ECC_STATUS,
+ NAND_NCE | NAND_CLE | NAND_CTRL_CHANGE);
+ ecc_status = chip->read_byte(mtd);
+ bitflips = ecc_status & 0xff;
+ mtd->ecc_stats.corrected += bitflips;


If above implementation cannot be acceptable, I would like to use "mtd->bitflip_threshold"
to inform number of bitflip, as the follows:

+ } else {
+ /*
+ * If can't use chip->cmd_ctrl,
+ * we can't get real number of bitflips.
+ * So, we set bitflips mtd->bitflip_threshold.
+ */
+ bitflips = mtd->bitflip_threshold;
+ mtd->ecc_stats.corrected += bitflips;
+ }
+ }
+
+ return bitflips;
+}

-- Yoshi

On 2015/06/16 22:53, Richard Weinberger wrote:
> Am 16.06.2015 um 15:33 schrieb KOBAYASHI Yoshitake:
>>>> + /* correctable */
>>>> + else if (status & NAND_STATUS_RECOM_REWRT) {
>>>> + pr_info("BENAND : Recommended to rewrite!\n");
>>>> + bitflips = chip->ecc.strength;
>>>
>>> In your case this might be okay, as you set strength to 1.
>>> Otherweise you'd have to report the real number of bitflips.
>>
>> I also thought it is okay in this case.
>> BENAND return corrected data to Host NAND Controller till uncorrectable status.
>> The current patch uses this Read Status command 70h to abstract BENAND Multi
>> bit ECC and Need to Rewrite judgement so BENAND would look like 1bit ECC device.
>
> The layers above MTD need to know how many bits got repaired.
> It seems like BENAND suffers from the same shortcomings than On-Die-ECC. ;-\
> Please see my patches how to deal with that. Maybe you can find a better solution.
>
> Thanks,
> //richard
>
>
>

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