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Date:   Tue, 11 Dec 2018 09:39:33 +0100
From:   Boris Brezillon <boris.brezillon@bootlin.com>
To:     Liang Yang <liang.yang@amlogic.com>
Cc:     Miquel Raynal <miquel.raynal@bootlin.com>,
        Jianxin Pan <jianxin.pan@amlogic.com>,
        <linux-mtd@lists.infradead.org>, Yixun Lan <yixun.lan@amlogic.com>,
        David Woodhouse <dwmw2@infradead.org>,
        Brian Norris <computersforpeace@gmail.com>,
        Marek Vasut <marek.vasut@gmail.com>,
        Richard Weinberger <richard@nod.at>,
        Jerome Brunet <jbrunet@baylibre.com>,
        Neil Armstrong <narmstrong@baylibre.com>,
        Martin Blumenstingl <martin.blumenstingl@googlemail.com>,
        Carlo Caione <carlo@caione.org>,
        Kevin Hilman <khilman@baylibre.com>,
        Rob Herring <robh@kernel.org>, Jian Hu <jian.hu@amlogic.com>,
        Hanjie Lin <hanjie.lin@amlogic.com>,
        Victor Wan <victor.wan@amlogic.com>,
        <linux-amlogic@lists.infradead.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v7 2/2] mtd: rawnand: meson: add support for Amlogic
 NAND flash controller
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On Tue, 11 Dec 2018 09:56:25 +0800
Liang Yang <liang.yang@amlogic.com> wrote:

> Hi Miquel,
> 
> On 2018/12/10 22:50, Miquel Raynal wrote:
> > Hi Liang,
> > 
> > Liang Yang <liang.yang@amlogic.com> wrote on Mon, 10 Dec 2018 20:12:39
> > +0800:
> >   
> >> On 2018/12/10 19:38, Boris Brezillon wrote:  
> >>> On Mon, 10 Dec 2018 19:23:46 +0800
> >>> Liang Yang <liang.yang@amlogic.com> wrote:
> >>>      
> >>>>>> +			mtd->ecc_stats.failed++;
> >>>>>> +			continue;
> >>>>>> +		}
> >>>>>> +		mtd->ecc_stats.corrected += ECC_ERR_CNT(*info);
> >>>>>> +		bitflips = max_t(u32, bitflips, ECC_ERR_CNT(*info));
> >>>>>> +	}  
> >>>>>
> >>>>> Are you sure you handle correctly empty pages with bf?  
> >>>>>     >> if scramble is enable, i would say yes here.  
> >>>> when scramble is disabled, i am considering how to use the helper
> >>>> nand_check_erased_ecc_chunk, but it seems that i can't get the ecc
> >>>> bytes which is caculated by ecc engine.by the way, nfc dma doesn't send
> >>>> out the ecc parity bytes.  
> >>>
> >>> Even if the ECC engine is disabled?
> >>>      
> >> No.
> >> When ECC engine is disabled, it can read the ecc parity bytes ; but there is another problem that i need to consider how code struct looks better when reading error with ecc opened and then try to raw read.
> >> Is there a good idea?  
> > 
> > When reading with ECC enabled, in case of uncorrectable error you
> > must re-read without ECC, then check if the page is empty or not with
> > the core helpers (nand_check_erased_*()).
> > 
> > Is this what you meant?
> >   
> yes. when uncorrectable ECC error, i need firstly read out the ECC bytes 
> without ECC engine and then use the helper nand_check_erased_ecc_chunk 
> to check if blank page.
> Of course, the precondition is without scrambler, or the bland page can 
> be detected by meson NFC.

Yep, raw accessors should disable both the scrambler and the ECC
engine (see what's done in sunxi_nand.c).