linux-kernel - Re: [PATCH 4/4] UBI: Implement bitrot checking

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Message-ID: <551D824D.3000004@nod.at>
Date:	Thu, 02 Apr 2015 19:54:21 +0200
From:	Richard Weinberger <richard@....at>
To:	Andrea Scian <rnd4@...e-tech.it>
CC:	linux-mtd@...ts.infradead.org, boris.brezillon@...e-electrons.com,
	linux-kernel@...r.kernel.org, dedekind1@...il.com
Subject: Re: [PATCH 4/4] UBI: Implement bitrot checking

Hi!

Am 02.04.2015 um 19:34 schrieb Andrea Scian:
> 
> Richard,
> 
> Il 29/03/2015 14:13, Richard Weinberger ha scritto:
>> +	mutex_lock(&ubi->buf_mutex);
>> +	err = ubi_io_read(ubi, ubi->peb_buf, e->pnum, 0, ubi->peb_size);
>> +	mutex_unlock(&ubi->buf_mutex);
>> +	if (err == UBI_IO_BITFLIPS) {
>> +		dbg_wl("found bitflips in PEB %d", e->pnum);
>> +		spin_lock(&ubi->wl_lock);
>> +
> 
> IIUC you trigger the action as soon as you have a bitflip error, is this
> correct?

I trigger it as soon UBI sees the bitflip. This depends on the configured MTD
bitflip_threshold.

> Isn't this too much conservative? You usually have a RBER on MLC devices
> that's between 1E-7 (for brand new devices) and 1E-4 (for devices with
> 1k-2k P/E cycle after 100k-300k read-without-P/E)
> 
> Having a few bitflips on a block read is more that usual and current ECC
> can correct more that 16 bit error over 512/1KiB.

Please see above. :)

Thanks,
//richard

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