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Date:   Wed, 10 Apr 2019 11:15:21 +0200
From:   Miquel Raynal <miquel.raynal@bootlin.com>
To:     masonccyang@mxic.com.tw
Cc:     bbrezillon@kernel.org,
        "Boris Brezillon" <boris.brezillon@collabora.com>,
        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: <20190410111521.026c7010@xps13>
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Hi masonccyang@mxic.com.tw,

masonccyang@mxic.com.tw wrote on Wed, 10 Apr 2019 16:40:25 +0800:

> Hi Miquel,
>  
> > > > 
> > > > 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?  

s/en/and/

> 
> yes !

I don't understand how this is possible. Have you tried it yourself?

Can you explain how this is supposed to work?

> 
> > 
> > And if randomized data is written to the NAND chip and we disable the
> > randomizer, then the data will also be correct?
> >   
> 
> Enable randomizer is a OTP(One-Time-Program) bit and can't be erased 
> again!
> That means never disable it once it has been enabled.
> 
> > > >   
> > > > > 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.  
> 
> yes, it is in ONFI param page@Byte# 167 of bit 1 (Vendor Blocks 
> starting@Byte# 164).
> 
> +#define ONFI_FEATURE_ADDR_MXIC_RANDOMIZER 0xB0
> +
> +struct nand_onfi_vendor_macronix {
> +                u8 reserved[1];
> +                u8 reliability_func;
> +} __packed;
> 
> 
> in addition, enable randomizer has no any impact on timing of tRC, tRP, 
> tWC and so on.
> host driver just need to check the status pin of RY/#BY as like standard
> read/write operation flow.
> 
> thanks & best regards,
> Mason
> 


Thanks,
Miquèl