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

From: Richard Weinberger <richard@nod.at>
To: Cheng Ming Lin <linchengming884@gmail.com>
Cc: chengzhihao1 <chengzhihao1@huawei.com>,
	 Miquel Raynal <miquel.raynal@bootlin.com>,
	 Vignesh Raghavendra <vigneshr@ti.com>,
	 linux-mtd <linux-mtd@lists.infradead.org>,
	 linux-kernel <linux-kernel@vger.kernel.org>,
	 Alvin Zhou <alvinzhou@mxic.com.tw>,
	leoyu@mxic.com.tw,  Cheng Ming Lin <chengminglin@mxic.com.tw>
Subject: Re: [RFC] mtd: ubi: skip programming unused bits in ubi headers
Date: Tue, 12 Aug 2025 08:57:08 +0200 (CEST)	[thread overview]
Message-ID: <152133202.103367.1754981828821.JavaMail.zimbra@nod.at> (raw)
In-Reply-To: <20250812051949.983040-1-linchengming884@gmail.com>

----- Ursprüngliche Mail -----
> Von: "Cheng Ming Lin" <linchengming884@gmail.com>
> An: "richard" <richard@nod.at>, "chengzhihao1" <chengzhihao1@huawei.com>, "Miquel Raynal" <miquel.raynal@bootlin.com>,
> "Vignesh Raghavendra" <vigneshr@ti.com>, "linux-mtd" <linux-mtd@lists.infradead.org>, "linux-kernel"
> <linux-kernel@vger.kernel.org>
> CC: "Alvin Zhou" <alvinzhou@mxic.com.tw>, leoyu@mxic.com.tw, "Cheng Ming Lin" <chengminglin@mxic.com.tw>
> Gesendet: Dienstag, 12. August 2025 07:19:49
> Betreff: [RFC] mtd: ubi: skip programming unused bits in ubi headers

> From: Cheng Ming Lin <chengminglin@mxic.com.tw>
> 
> This patch prevents unnecessary programming of bits in ec_hdr and
> vid_hdr that are not used or read during normal UBI operation. These
> unused bits are typically already set to 1 in erased flash and do not
> need to be explicitly programmed to 0 if they are not used.
> 
> Programming such unused areas offers no functional benefit and may
> result in unnecessary flash wear, reducing the overall lifetime of the
> device. By skipping these writes, we preserve the flash state as much
> as possible and minimize wear caused by redundant operations.

We talk about programming a single (sub)page, right?

> This change ensures that only necessary fields are written when
> preparing UBI headers, improving flash efficiency without affecting
> functionality.

I have been told that writing 0xFF bytes to NAND should be avoided.
This is also why UBI initializes them to 0x00.

Do you have data which proves the opposite?

Thanks,
//richard

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