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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 <leoyu@mxic.com.tw>,
	 Cheng Ming Lin <chengminglin@mxic.com.tw>
Subject: Re: [RFC] mtd: ubi: skip programming unused bits in ubi headers
Date: Thu, 14 Aug 2025 13:30:13 +0200 (CEST)	[thread overview]
Message-ID: <608935583.115196.1755171013804.JavaMail.zimbra@nod.at> (raw)
In-Reply-To: <CAAyq3SaEqYiKhbjYwLH0p6F2G=UR-MwZF28AG1xVMoKhznS3Og@mail.gmail.com>

----- Ursprüngliche Mail -----
> Von: "Cheng Ming Lin" <linchengming884@gmail.com>
>> I have been told that writing 0xFF bytes to NAND should be avoided.
>> This is also why UBI initializes them to 0x00.
> 
> Normally, after a NAND flash block is erased, all bits are in the 0xFF
> state. Programming 0xFF in this case will not actually change the NAND
> cells, as the device can inhibit programming—either by raising the
> bitline voltage or using a self-boosted program inhibit mechanism.
> Therefore, programming 0xFF is a normal and harmless operation for NAND
> flash.

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.

Thanks,
//richard


______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

WARNING: multiple messages have this Message-ID (diff)
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 <leoyu@mxic.com.tw>,
	 Cheng Ming Lin <chengminglin@mxic.com.tw>
Subject: Re: [RFC] mtd: ubi: skip programming unused bits in ubi headers
Date: Thu, 14 Aug 2025 13:30:13 +0200 (CEST)	[thread overview]
Message-ID: <608935583.115196.1755171013804.JavaMail.zimbra@nod.at> (raw)
In-Reply-To: <CAAyq3SaEqYiKhbjYwLH0p6F2G=UR-MwZF28AG1xVMoKhznS3Og@mail.gmail.com>

----- Ursprüngliche Mail -----
> Von: "Cheng Ming Lin" <linchengming884@gmail.com>
>> I have been told that writing 0xFF bytes to NAND should be avoided.
>> This is also why UBI initializes them to 0x00.
> 
> Normally, after a NAND flash block is erased, all bits are in the 0xFF
> state. Programming 0xFF in this case will not actually change the NAND
> cells, as the device can inhibit programming—either by raising the
> bitline voltage or using a self-boosted program inhibit mechanism.
> Therefore, programming 0xFF is a normal and harmless operation for NAND
> flash.

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.

Thanks,
//richard


  reply	other threads:[~2025-08-14 14:31 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-08-12  5:19 [RFC] mtd: ubi: skip programming unused bits in ubi headers Cheng Ming Lin
2025-08-12  5:19 ` Cheng Ming Lin
2025-08-12  6:57 ` Richard Weinberger
2025-08-12  6:57   ` Richard Weinberger
2025-08-14 10:11   ` Cheng Ming Lin
2025-08-14 10:11     ` Cheng Ming Lin
2025-08-14 11:30     ` Richard Weinberger [this message]
2025-08-14 11:30       ` Richard Weinberger
2025-09-05  3:21       ` Cheng Ming Lin
2025-09-05  3:21         ` Cheng Ming Lin
2025-09-12  7:57         ` Richard Weinberger
2025-09-12  7:57           ` Richard Weinberger
2025-09-12  7:57           ` Cheng Ming Lin
2025-09-12  7:57             ` Cheng Ming Lin
2025-09-12  8:04             ` Richard Weinberger
2025-09-12  8:04               ` Richard Weinberger
2025-09-12  8:19               ` Cheng Ming Lin
2025-09-12  8:19                 ` Cheng Ming Lin

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