RE: [LINUX PATCH v17 1/2] mtd: rawnand: nand_micron: Do not over write driver's read_page()/write_page()

[Naga Sureshkumar Relli <nagasure@xilinx.com>]

Hi Boris,

> -----Original Message-----
> From: Boris Brezillon <boris.brezillon@collabora.com>
> Sent: Wednesday, June 26, 2019 5:34 PM
> To: Naga Sureshkumar Relli <nagasure@xilinx.com>
> Cc: miquel.raynal@bootlin.com; helmut.grohne@intenta.de; richard@nod.at;
> dwmw2@infradead.org; computersforpeace@gmail.com; marek.vasut@gmail.com;
> vigneshr@ti.com; bbrezillon@kernel.org; yamada.masahiro@socionext.com; linux-
> mtd@lists.infradead.org; linux-kernel@vger.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@xilinx.com> wrote:
> 
> > Hi Boris,
> >
> > > -----Original Message-----
> > > From: Boris Brezillon <boris.brezillon@collabora.com>
> > > Sent: Wednesday, June 26, 2019 4:57 PM
> > > To: Naga Sureshkumar Relli <nagasure@xilinx.com>
> > > Cc: miquel.raynal@bootlin.com; helmut.grohne@intenta.de;
> > > richard@nod.at; dwmw2@infradead.org; computersforpeace@gmail.com;
> > > marek.vasut@gmail.com; vigneshr@ti.com; bbrezillon@kernel.org;
> > > yamada.masahiro@socionext.com; linux- mtd@lists.infradead.org;
> > > linux-kernel@vger.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@xilinx.com> wrote:
> > >
> > > > Hi Boris,
> > > >
> > > > > -----Original Message-----
> > > > > From: Boris Brezillon <boris.brezillon@collabora.com>
> > > > > Sent: Wednesday, June 26, 2019 12:18 PM
> > > > > To: Naga Sureshkumar Relli <nagasure@xilinx.com>
> > > > > Cc: miquel.raynal@bootlin.com; helmut.grohne@intenta.de;
> > > > > richard@nod.at; dwmw2@infradead.org;
> > > > > computersforpeace@gmail.com; marek.vasut@gmail.com;
> > > > > vigneshr@ti.com; bbrezillon@kernel.org;
> > > > > yamada.masahiro@socionext.com; linux- mtd@lists.infradead.org;
> > > > > linux-kernel@vger.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@xilinx.com> wrote:
> > > > >
> > > > > > Add check before assigning chip->ecc.read_page() and
> > > > > > chip->ecc.write_page()
> > > > > >
> > > > > > Signed-off-by: Naga Sureshkumar Relli
> > > > > > <naga.sureshkumar.relli@xilinx.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.
Yes, we can assert/de-assert CS on each read/write_data_op().
But what about transfer length splitting?
+	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);
This should be done as a part of pl353_raw_read/write() right?

Thanks,
Naga Sureshkumar Relli