linux-kernel - Re: [PATCH] mtd: denali: Disable sub-page writes in Denali NAND driver

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Date:	Fri, 06 Feb 2015 10:28:53 +0100
From:	Richard Weinberger <richard@....at>
To:	Ricard Wanderlof <ricard.wanderlof@...s.com>,
	Graham Moore <grmoore@...nsource.altera.com>
CC:	Dinh Nguyen <dinh.linux@...il.com>,
	Josh Triplett <josh@...htriplett.org>,
	Linux List <linux-kernel@...r.kernel.org>,
	"yamada.m@...panasonic.com" <yamada.m@...panasonic.com>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	Dinh Nguyen <dinguyen@...nsource.altera.com>,
	Brian Norris <computersforpeace@...il.com>,
	David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH] mtd: denali: Disable sub-page writes in Denali NAND driver

Am 06.02.2015 um 09:29 schrieb Ricard Wanderlof:
> 
> On Thu, 5 Feb 2015, Graham Moore wrote:
> 
>> Actually, we made this change to make UBIFS work.  So, yes, the driver 
>> never worked for UBI.  Worked fine for JFFS2, raw data.
>>
>> A customer reported an issue with ECC errors when using UBIFS on NAND 
>> flash with Altera SoC.
>>
>> We debugged it and found the ECC errors occur because the UBI subsystem 
>> is trying to write sub-pages in the NAND, but neither the NAND chip 
>> itself nor the Denali NAND controller support sub-page writes.
> 
> Just a bit curious.
> 
> It is not uncommon for controllers or chips not to support sub-page 
> writes. In that case however, the partition(s) used by UBI should be 
> formatted accordingly, i.e. using the appropriate --sub-page-size argument 
> to ubiformat (when formatting partitions on the system itself), or the 
> corresponding argument to ubinize (when preparing images offline).
> 
> If that is done correctly, then the lack of subpage write capability is 
> not a problem per se (of course, the UBI EC and VID headers then take up 
> more space so less space is available for user data; on a flash with 2k 
> pages it is only 2k bytes per LEB that is lost however).

Yeah, but UBI automatically will use subpages unless you specify
use the vid_hdr_offs parameter.
IOW, if the driver advertises subpages UBI will use them.

Thanks,
//richard
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