RE: [EXT] [PATCH v2 3/3] mtd: rawnand: micron: Address the shallow erase issue

From: "Bean Huo (beanhuo)" <beanhuo@micron.com>
To: Boris Brezillon <boris.brezillon@collabora.com>,
	Richard Weinberger <richard@nod.at>
Cc: Vignesh Raghavendra <vigneshr@ti.com>,
	Tudor Ambarus <Tudor.Ambarus@microchip.com>,
	Steve deRosier <derosier@gmail.com>,
	"Zoltan Szubbocsev \(zszubbocsev\)" <zszubbocsev@micron.com>,
	"linux-mtd@lists.infradead.org" <linux-mtd@lists.infradead.org>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	Miquel Raynal <miquel.raynal@bootlin.com>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	Piotr Wojtaszczyk <WojtaszczykP@cumminsallison.com>
Subject: RE: [EXT] [PATCH v2 3/3] mtd: rawnand: micron: Address the shallow erase issue
Date: Wed, 6 May 2020 15:50:32 +0000	[thread overview]
Message-ID: <BN7PR08MB5684D8DFC50CB93B53705619DBA40@BN7PR08MB5684.namprd08.prod.outlook.com> (raw)
In-Reply-To: <20200506104522.6c90f88f@collabora.com>

Hi, Boris

> 
> On Wed, 6 May 2020 08:28:43 +0000
> "Bean Huo (beanhuo)" <beanhuo@micron.com> wrote:
> 
> > Hi, Miquel
> > I have two questions about your patch, please help me.
> >
> > > +	 */
> > > +	for (eb = first_eb; eb < first_eb + nb_eb; eb++) {
> > > +		/* Il all the first pages are not written yet, do it */
> > > +		if (micron->writtenp[eb] != MICRON_PAGE_MASK_TRIGGER)
> > > +			micron_nand_avoid_shallow_erase(chip, eb);
> > > +
> > > +		micron->writtenp[eb] = 0;
> > > +	}
> >
> >
> > Here, if the power loss happens before erasing this block, for the
> > next time boot up, What will happen from FS layer in case FS detect this filled
> data?
> 
> Most likely ECC errors will be returned, but that doesn't matter since this block
> was about to be erased. You have pretty much the same problem for partially
> erase blocks already, and that should be handled by the wear-leveling/FS, if not,
> that would be bug (note that it's properly handled by UBI, which just considers
> the block as invalid and schedules an erase).
> 

Concerning this, I still have question, for the UBIFS,  If I am correct, there are
EC and VID header both being damaged, then UBIFS will re-erase it. I don't know if
UBIFS can handle there is dirty/filling data in the some pages  and EC/VID valid.
Maybe Richard has fixed it.

> >
> > This micron->written is stored in the system memory, once power cut,
> > for the next time Boot up, will it be reinstated or it will be 0x00?
> 
> Yep, and that shouldn't be a problem, it just means we might have unneeded
> page writes if the pages were already written, but, other than the perf penalty it
> incurs, it should work fine.
> 
> We can optimize that a bit by adding a ->post_read_page() hook so we can flag
> already read pages as written/erased and avoid those unneeded writes in some
> situations.

That means we assume this block being read before erasing.

Thanks,

Bean

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