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To: Bruce M Simpson <bms@incunabulum.net>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Mon, 17 Dec 2007 15:26:19 GMT."
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Date: Tue, 18 Dec 2007 00:16:37 +0000
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Cc: cvs-src@FreeBSD.org, src-committers@FreeBSD.org,
	"Bruce M. Simpson" <bms@FreeBSD.org>, cvs-all@FreeBSD.org
Subject: Re: cvs commit: src/sbin/atacontrol atacontrol.c 
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In message <4766951B.8090504@incunabulum.net>, Bruce M Simpson writes:

>Ah, let me rephrase, I meant:
>
>* NAND Flash embedded ATA controllers should not erase sectors 
>containing data unless absolutely necessary, to implement wear levelling.

That's part of the job description, but it is more complex than that.

> * BIO_DELETE provides the necessary hint from the OS, by way of the ATA 
>CFA ERASE command, to tell the flash controller that the upper layer 
>consumer of the blocks has marked the data as being erased.

Yes.

> * The NAND flash ATA controller is *then* in a position to know how 
>best to implement that wear levelling as the OS has told it "I'm not 
>using these sectors any more".

Possibly.  For "best" substitute "better" and I might agree.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.