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Date:   Wed, 10 Apr 2019 09:16:12 +0200
From:   Miquel Raynal <miquel.raynal@bootlin.com>
To:     masonccyang@mxic.com.tw
Cc:     "Boris Brezillon" <boris.brezillon@collabora.com>,
        bbrezillon@kernel.org, computersforpeace@gmail.com,
        dwmw2@infradead.org, juliensu@mxic.com.tw,
        linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org,
        marek.vasut@gmail.com, richard@nod.at, zhengxunli@mxic.com.tw
Subject: Re: [PATCH] mtd: rawnand: Add Macronix NAND read retry and
 randomizer support
Message-ID: <20190410091612.229c91b4@xps13>
In-Reply-To: <OF9601E14B.A48284C4-ON482583D8.0005E3EB-482583D8.0006CC14@mxic.com.tw>
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        <OF6C97E4DE.45261545-ON482583D7.00340468-482583D7.0034B3FE@mxic.com.tw>
        <20190409114701.744c2c8c@collabora.com>
        <OF9601E14B.A48284C4-ON482583D8.0005E3EB-482583D8.0006CC14@mxic.com.tw>
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Hi Mason,

masonccyang@mxic.com.tw wrote on Wed, 10 Apr 2019 09:14:14 +0800:

> Hi Boris,
> 
> > 
> > Subject
> > 
> > Re: [PATCH] mtd: rawnand: Add Macronix NAND read retry and randomizer   
> support
> > 
> > On Tue, 9 Apr 2019 17:35:39 +0800
> > masonccyang@mxic.com.tw wrote:
> >   
> > > > > +
> > > > > +static const struct kobj_attribute sysfs_mxic_nand =
> > > > > +   __ATTR(nand_random, S_IRUGO | S_IWUSR,
> > > > > +          mxic_nand_rand_type_show,
> > > > > +          mxic_nand_rand_type_store);   
> > > > 
> > > > No, we don't want to expose that through a sysfs file, especially   
> since
> > > > changing the randomizer config means making the NAND unreadable for
> > > > those that have used it before the change.
> > > >   
> > > 
> > > Our on-die randomizer is still readable from user after the function 
> > > is enabled.  
> > 
> > You mean the memory is still readable no matter the randomizer state.
> > Not sure how that's possible, but okay.

So if you write non-randomized data to the NAND chip, then enable the
randomizer en read back the data, all will be ok?

And if randomized data is written to the NAND chip and we disable the
randomizer, then the data will also be correct?

> >   
> > > This randomizer is just like a internal memory cell 
> > > reliability enhanced.  
> > 
> > Why don't you enable it by default then?  
> 
> The penalty of randomizer is read/write performance down.
> i.e,. tPROG 300 us to 340 us (randomizer enable)
> therefore, disable it by default.

Is this info somewhere in the ONFI param page? I suppose once
randomization is enabled we should also tweak the timings and verify
that the controller supports it.

> > > It could be enable at any time with OTP bit function and that's why
> > > we patch it by sys-fs.  
> > 
> > Sorry, but that's not a good reason to expose that through sysfs.  
> 
> Any good way to expose randomizer function for user ?
> 
> thanks & best regards,
> Mason
> 

Thanks,
Miquèl