linux-kernel - Re: [PATCH 0/2] Fix double counting of S/W ECC engines' ECC stat

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Message-ID: <OF12EB0BE9.7879DE49-ON482586DB.0039FC49-482586DB.003C2449@mxic.com.tw>
Date:   Thu, 20 May 2021 18:56:54 +0800
From:   ycllin@...c.com.tw
To:     "Miquel Raynal" <miquel.raynal@...tlin.com>
Cc:     juliensu@...c.com.tw, linux-kernel@...r.kernel.org,
        linux-mtd@...ts.infradead.org, richard@....at,
        "Thomas Petazzoni" <thomas.petazzoni@...tlin.com>, vigneshr@...com
Subject: Re: [PATCH 0/2] Fix double counting of S/W ECC engines' ECC stat

Hi Miquèl,

> "Miquel Raynal" <miquel.raynal@...tlin.com> 
> Re: [PATCH 0/2] Fix double counting of S/W ECC engines' ECC stat
> 
> Hi YouChing,
> 
> ycllin@...c.com.tw wrote on Thu, 13 May 2021 10:11:02 +0800:
> 
> > > "Miquel Raynal" <miquel.raynal@...tlin.com> 
> > <deleted>
> > > 
> > > Good catch!
> > > 
> > > However I don't think the current fix is valid because these engines
> > > are meant to be used by the raw NAND core as well, I propose 
something
> > > like the below, can you please tell me if it works as expected? (not
> > > even build tested)
> > > 
> > > Thanks,
> > > Miquèl
> > > 
> > > 
> > <deleted>
> > 
> > Thanks for your work.
> > 
> > I tested the two patches(yours and mine) separately in our 
environment: 
> > 1) MXIC NFC(&raw NAND),2) MXIC SPI host(&SPI-NAND) with S/W BCH 
engine. 
> > Both patches are valid(using nandtest/nandbiterrs, values of ecc_stats 
are 
> > normal).
> > 
> > This seems to be because the function(nand_ecc_sw_bch_finish_io_req() 
> > in ecc-sw-bch.c) that would increase the ecc_stats counter is not used 

> > in the raw NAND world. Am I misunderstanding or is it platform 
dependency?
> 
> I don't think it can be called a platform dependency, it's more like
> legacy from the raw NAND world which makes the use of the generic ECC
> framework hard and thus is limited to a given set of functions.
> 
> > BTW, I think your modification should be more in line with the design 
> > spirit 
> > of generic ECC engine framework.
> 
> Yes, ideally raw NAND should fully comply to this framework but this
> would require a hundred days of work and dozens of available boards to
> test. During the past 20 years people assumed NAND controller and ECC
> engine were a single entity which makes the use of the generic ECC
> framework hard to implemented in the raw NAND. So I decided not to put
> all my energy there in order to first get this framework available to
> SPI-NAND devices.

Thanks for your detailed explanation. 
I agree with your change and it works fine in SPI-NAND world 
(with on-die or S/W ECC engines) and raw NAND world(with S/W ECC engines).

Tested-by: YouChing Lin <ycllin@...c.com.tw>

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