linux-kernel - Re: [PATCH v2] mtd: nand: brcmnand: fix mtd corrected bits stat

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Message-ID: <8734c9z2ye.fsf@bootlin.com>
Date: Mon, 09 Jun 2025 11:20:09 +0200
From: Miquel Raynal <miquel.raynal@...tlin.com>
To: David Regan <dregan@...adcom.com>
Cc: linux-kernel@...r.kernel.org,  linux-mtd@...ts.infradead.org,
  bcm-kernel-feedback-list@...adcom.com,  william.zhang@...adcom.com,
  anand.gore@...adcom.com,  florian.fainelli@...adcom.com,
  kamal.dasu@...adcom.com,  dan.beygelman@...adcom.com,  Álvaro Fernández
 Rojas <noltari@...il.com>,  rafal@...ecki.pl,
  computersforpeace@...il.com,  frieder.schrempf@...tron.de,
  vigneshr@...com,  richard@....at,  bbrezillon@...nel.org,
  kdasu.kdev@...il.com,  jaimeliao.tw@...il.com,  kilobyte@...band.pl,
  jonas.gorski@...il.com,  dgcbueu@...il.com,  dregan@...l.com
Subject: Re: [PATCH v2] mtd: nand: brcmnand: fix mtd corrected bits stat

On 06/06/2025 at 09:57:03 -07, David Regan <dregan@...adcom.com> wrote:

> Currently we attempt to get the amount of flipped bits from a hardware
> location which is reset on every subpage. Instead obtain total flipped
> bits stat from hardware accumulator. In addition identify the correct
> maximum subpage corrected bits.
>
> Signed-off-by: David Regan <dregan@...adcom.com>
> Reviewed-by: William Zhang <william.zhang@...adcom.com>
> ---

Hello,

Can you please give the output of nandbiterrs -i /dev/mtdX?

>  v2: Add >= v4 NAND controller support as requested by Jonas.
>      mtd->ecc_stats.corrected accumulates instead of set to total.
>      Remove DMA specific flipped bits count.

The changelog does not mention the fact that you return the maximum
number of corrected bitflips as I requested, and the diff does not show
a straightforward implementation of that. It is very important to get
this right.

If we take the following example of a page with 4 ECC steps, if we get
respectively: 0, 2, 3, 0 bitflips per step, the returned value shall be
3.

To be very certain that this is correct, you can use the nandflipbit
tool from the mtd-utils test suite. You can manually insert bitflips in
various areas of a page and then read the page again with ECC enabled
and see how many bit errors are reported.

Thanks,
Miquèl