linux-kernel - Re: [RFC] mtd: ubi: skip programming unused bits in ubi headers

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Message-ID: <1899901955.27456.1757663848457.JavaMail.zimbra@nod.at>
Date: Fri, 12 Sep 2025 09:57:28 +0200 (CEST)
From: Richard Weinberger <richard@....at>
To: Cheng Ming Lin <linchengming884@...il.com>
Cc: chengzhihao1 <chengzhihao1@...wei.com>, 
	Miquel Raynal <miquel.raynal@...tlin.com>, 
	Vignesh Raghavendra <vigneshr@...com>, 
	linux-mtd <linux-mtd@...ts.infradead.org>, 
	linux-kernel <linux-kernel@...r.kernel.org>, 
	Alvin Zhou <alvinzhou@...c.com.tw>, leoyu <leoyu@...c.com.tw>, 
	Cheng Ming Lin <chengminglin@...c.com.tw>
Subject: Re: [RFC] mtd: ubi: skip programming unused bits in ubi headers

----- Ursprüngliche Mail -----
> Von: "Cheng Ming Lin" <linchengming884@...il.com>
>> That's the crucial question. Is this true for all NAND chips?
>> Do avoid larger writes of 0xFF patterns file systems such as UBIFS
>> also use compression a lot.
>> At least that's what I have been told when I asked 10+ years ago
>> how UBI works.
> 
> You are correct that there is an issue when blank data pages are repeatedly
> erased. This can lead to cells entering a too deep VT state, which may
> cause program failures in subsequent operations.
> 
> To address this, newer NAND generations typically perform a pre-program
> step before executing the actual erase. This keeps the VT distribution from
> going too deep, thereby avoiding the blank-page degradation problem.
> Such pre-PGM techniques have been widely adopted for roughly the past
> 10–15 years.
> 
> Additionally, JESD22-A117E (page 6, section 4.1.2.1) specifies examples of
> acceptable data patterns, including solid-programmed, checkerboard/inverse-
> checkerboard, and checkerboard-with-fill patterns. According to
> qualification knowledge bases, using 0x00 can sometimes trigger special
> failure modes, whereas writing 0xFF is more robust.
> 
> Additionally, the Kioxia TC58NVG1S3HTA00 datasheet (page 63) also notes
> that continuous program/erase cycling with a high percentage of ‘0'
> bits in the data pattern can accelerate block endurance degradation.
> This further supports avoiding large 0x00 patterns.

Thanks for the detailed answer!
So, yes let's apply this change.

Thanks,
//richard