Re: [RESEND v5 07/21] mtd: rawnand: Create a new enumeration to describe OOB placement

From: Boris Brezillon <boris.brezillon@collabora.com>
To: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	devicetree@vger.kernel.org, Vignesh Raghavendra <vigneshr@ti.com>,
	Tudor Ambarus <Tudor.Ambarus@microchip.com>,
	Richard Weinberger <richard@nod.at>,
	Rob Herring <robh+dt@kernel.org>,
	linux-mtd@lists.infradead.org
Subject: Re: [RESEND v5 07/21] mtd: rawnand: Create a new enumeration to describe OOB placement
Date: Wed, 27 May 2020 10:22:57 +0200	[thread overview]
Message-ID: <20200527102257.788fc5a0@collabora.com> (raw)
In-Reply-To: <20200527100050.7e54713a@xps13>

On Wed, 27 May 2020 10:00:50 +0200
Miquel Raynal <miquel.raynal@bootlin.com> wrote:

> Hi Boris,
> 
> Boris Brezillon <boris.brezillon@collabora.com> wrote on Wed, 27 May
> 2020 00:39:04 +0200:
> 
> > On Tue, 26 May 2020 21:56:19 +0200
> > Miquel Raynal <miquel.raynal@bootlin.com> wrote:
> >   
> > > There is currently a confusion between the ECC type/mode/provider
> > > (eg. hardware, software, on-die or none) and the ECC bytes placement.
> > > 
> > > Create a new enumeration to describe this placement.
> > > 
> > > Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> > > Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
> > > ---
> > >  drivers/mtd/nand/raw/nand_base.c |  4 ++++
> > >  include/linux/mtd/rawnand.h      | 12 ++++++++++++
> > >  2 files changed, 16 insertions(+)
> > > 
> > > diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
> > > index ef70ca0828c3..a4470a19c805 100644
> > > --- a/drivers/mtd/nand/raw/nand_base.c
> > > +++ b/drivers/mtd/nand/raw/nand_base.c
> > > @@ -5018,6 +5018,10 @@ static const char * const nand_ecc_modes[] = {
> > >  	[NAND_ECC_ON_DIE]	= "on-die",
> > >  };
> > >  
> > > +static const char * const nand_ecc_placement[] = {
> > > +	[NAND_ECC_PLACEMENT_INTERLEAVED] = "interleaved",
> > > +};
> > > +
> > >  static int of_get_nand_ecc_mode(struct device_node *np)
> > >  {
> > >  	const char *pm;
> > > diff --git a/include/linux/mtd/rawnand.h b/include/linux/mtd/rawnand.h
> > > index 8187056dd3a0..6eb4d91b07eb 100644
> > > --- a/include/linux/mtd/rawnand.h
> > > +++ b/include/linux/mtd/rawnand.h
> > > @@ -92,6 +92,18 @@ enum nand_ecc_mode {
> > >  	NAND_ECC_ON_DIE,
> > >  };
> > >  
> > > +/**
> > > + * enum nand_ecc_placement - NAND ECC placement
> > > + * @NAND_ECC_PLACEMENT_FREE: The driver can decide where to put ECC bytes.    
> > 
> > Can we name that one UNDEFINED instead of FREE, and it's not really the
> > driver that decides (unless you have a choice or use SW ECC), more the ECC
> > engine itself.  
> 
> Ack.
> 
> >   
> > > + *                           Default behavior is to put them at the end of the
> > > + *                           OOB area.    
> > 
> > I wouldn't even define a default behavior here, but instead add a value for
> > OOB/TAIL placement.  
> 
> This is for legacy reasons, maybe I should not say it is a default, but
> rather a common location (or say nothing).

I wouldn't even mention what the most common pattern is. But I think
defining @NAND_ECC_PLACEMENT_OOB is a good thing.

> 
> >   
> > > + * @NAND_ECC_PLACEMENT_INTERLEAVED: Syndrome layout: interleave data and OOB.    
> > 
> > 
> > 									     ^ECC bytes
> >   
> > > + */
> > > +enum nand_ecc_placement {
> > > +	NAND_ECC_PLACEMENT_FREE,
> > > +	NAND_ECC_PLACEMENT_INTERLEAVED,
> > > +};
> > > +
> > >  enum nand_ecc_algo {
> > >  	NAND_ECC_UNKNOWN,
> > >  	NAND_ECC_HAMMING,    
> >   

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