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

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Message-ID: <87ecw2ns3s.fsf@bootlin.com>
Date: Mon, 02 Jun 2025 16:19:35 +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] mtd: nand: brcmnand: fix mtd corrected bits stat

On 29/05/2025 at 20:46:59 -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.

This change does not feel correct. We gather two statistics:
- the maximum number of bitflips corrected in a single ECC chunk
- the total number of bitflips among the whole page

The most important one is the former, because it may trigger wear
levelling from the top layer (UBI, usually). It feels like you are
breaking this, am I wrong? Would you mind to be more explicit otherwise?

Thanks,
Miquèl