linux-kernel - Re: [LINUX PATCH v17 1/2] mtd: rawnand: nand_micron: Do not over write driver's read_page()/write

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Date:   Wed, 26 Jun 2019 14:04:17 +0200
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     Naga Sureshkumar Relli <nagasure@...inx.com>
Cc:     "miquel.raynal@...tlin.com" <miquel.raynal@...tlin.com>,
        "helmut.grohne@...enta.de" <helmut.grohne@...enta.de>,
        "richard@....at" <richard@....at>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "computersforpeace@...il.com" <computersforpeace@...il.com>,
        "marek.vasut@...il.com" <marek.vasut@...il.com>,
        "vigneshr@...com" <vigneshr@...com>,
        "bbrezillon@...nel.org" <bbrezillon@...nel.org>,
        "yamada.masahiro@...ionext.com" <yamada.masahiro@...ionext.com>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [LINUX PATCH v17 1/2] mtd: rawnand: nand_micron: Do not over
 write driver's read_page()/write_page()

On Wed, 26 Jun 2019 11:51:12 +0000
Naga Sureshkumar Relli <nagasure@...inx.com> wrote:

> Hi Boris,
> 
> > -----Original Message-----
> > From: Boris Brezillon <boris.brezillon@...labora.com>
> > Sent: Wednesday, June 26, 2019 4:57 PM
> > To: Naga Sureshkumar Relli <nagasure@...inx.com>
> > Cc: miquel.raynal@...tlin.com; helmut.grohne@...enta.de; richard@....at;
> > dwmw2@...radead.org; computersforpeace@...il.com; marek.vasut@...il.com;
> > vigneshr@...com; bbrezillon@...nel.org; yamada.masahiro@...ionext.com; linux-
> > mtd@...ts.infradead.org; linux-kernel@...r.kernel.org
> > Subject: Re: [LINUX PATCH v17 1/2] mtd: rawnand: nand_micron: Do not over write
> > driver's read_page()/write_page()
> > 
> > On Wed, 26 Jun 2019 11:22:33 +0000
> > Naga Sureshkumar Relli <nagasure@...inx.com> wrote:
> >   
> > > Hi Boris,
> > >  
> > > > -----Original Message-----
> > > > From: Boris Brezillon <boris.brezillon@...labora.com>
> > > > Sent: Wednesday, June 26, 2019 12:18 PM
> > > > To: Naga Sureshkumar Relli <nagasure@...inx.com>
> > > > Cc: miquel.raynal@...tlin.com; helmut.grohne@...enta.de;
> > > > richard@....at; dwmw2@...radead.org; computersforpeace@...il.com;
> > > > marek.vasut@...il.com; vigneshr@...com; bbrezillon@...nel.org;
> > > > yamada.masahiro@...ionext.com; linux- mtd@...ts.infradead.org;
> > > > linux-kernel@...r.kernel.org
> > > > Subject: Re: [LINUX PATCH v17 1/2] mtd: rawnand: nand_micron: Do not
> > > > over write driver's read_page()/write_page()
> > > >
> > > > On Mon, 24 Jun 2019 22:46:29 -0600
> > > > Naga Sureshkumar Relli <naga.sureshkumar.relli@...inx.com> wrote:
> > > >  
> > > > > Add check before assigning chip->ecc.read_page() and
> > > > > chip->ecc.write_page()
> > > > >
> > > > > Signed-off-by: Naga Sureshkumar Relli
> > > > > <naga.sureshkumar.relli@...inx.com>
> > > > > ---
> > > > >  drivers/mtd/nand/raw/nand_micron.c | 7 +++++--
> > > > >  1 file changed, 5 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/drivers/mtd/nand/raw/nand_micron.c
> > > > > b/drivers/mtd/nand/raw/nand_micron.c
> > > > > index cbd4f09ac178..565f2696c747 100644
> > > > > --- a/drivers/mtd/nand/raw/nand_micron.c
> > > > > +++ b/drivers/mtd/nand/raw/nand_micron.c
> > > > > @@ -500,8 +500,11 @@ static int micron_nand_init(struct nand_chip *chip)
> > > > >  		chip->ecc.size = 512;
> > > > >  		chip->ecc.strength = chip->base.eccreq.strength;
> > > > >  		chip->ecc.algo = NAND_ECC_BCH;
> > > > > -		chip->ecc.read_page = micron_nand_read_page_on_die_ecc;
> > > > > -		chip->ecc.write_page = micron_nand_write_page_on_die_ecc;
> > > > > +		if (!chip->ecc.read_page)
> > > > > +			chip->ecc.read_page = micron_nand_read_page_on_die_ecc;
> > > > > +
> > > > > +		if (!chip->ecc.write_page)
> > > > > +			chip->ecc.write_page = micron_nand_write_page_on_die_ecc;  
> > > >
> > > > That's wrong, if you don't want on-die ECC to be used, simply don't
> > > > set nand-ecc-mode to "on- die".  
> > > Ok. But if we want to use on-die ECC then you mean to say it is mandatory to use  
> > micron_nand_read/write_page_on_die_ecc()?
> > 
> > Absolutely, and if it doesn't work that means you driver does not
> > implement raw accesses correctly, which means it's still buggy...  
> I agree. But let's say, if there is a limitation with the controller. Then it is must to have this check right?
> I mean, for pl353 controller, we must clear the CS during the data phase, hence we are splitting the 
> Transfer in the pl353_read/write_page_raw().
> +	pl353_nand_read_data_op(chip, buf, mtd->writesize, false);
> +	p = chip->oob_poi;
> +	pl353_nand_read_data_op(chip, p,
> +				(mtd->oobsize -
> +				PL353_NAND_LAST_TRANSFER_LENGTH), false);
> +	p += (mtd->oobsize - PL353_NAND_LAST_TRANSFER_LENGTH);
> +	xnfc->dataphase_addrflags |= PL353_NAND_CLEAR_CS;
> +	pl353_nand_read_data_op(chip, p, PL353_NAND_LAST_TRANSFER_LENGTH,
> +				false);
> As the above sequence is needed even for raw access, PL353 is unable to use the on_die_page reads.

This "de-assert CS on last access" logic should be done in the
exec_op() implementation. I also wonder how that works for operations
that don't have data cycles. Oh, BTW, most chips are CE-don't-care,
which means you can assert/de-assert CS on each read_data_op() without
any issues.