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

[Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>]

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

> Hi Boris,
> 
> > -----Original Message-----
> > From: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
> > Sent: Wednesday, June 26, 2019 4:57 PM
> > To: Naga Sureshkumar Relli <nagasure@xxxxxxxxxx>
> > Cc: miquel.raynal@xxxxxxxxxxx; helmut.grohne@xxxxxxxxxx; richard@xxxxxx;
> > dwmw2@xxxxxxxxxxxxx; computersforpeace@xxxxxxxxx; marek.vasut@xxxxxxxxx;
> > vigneshr@xxxxxx; bbrezillon@xxxxxxxxxx; yamada.masahiro@xxxxxxxxxxxxx; linux-
> > mtd@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> > 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@xxxxxxxxxx> wrote:
> >   
> > > Hi Boris,
> > >  
> > > > -----Original Message-----
> > > > From: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
> > > > Sent: Wednesday, June 26, 2019 12:18 PM
> > > > To: Naga Sureshkumar Relli <nagasure@xxxxxxxxxx>
> > > > Cc: miquel.raynal@xxxxxxxxxxx; helmut.grohne@xxxxxxxxxx;
> > > > richard@xxxxxx; dwmw2@xxxxxxxxxxxxx; computersforpeace@xxxxxxxxx;
> > > > marek.vasut@xxxxxxxxx; vigneshr@xxxxxx; bbrezillon@xxxxxxxxxx;
> > > > yamada.masahiro@xxxxxxxxxxxxx; linux- mtd@xxxxxxxxxxxxxxxxxxx;
> > > > linux-kernel@xxxxxxxxxxxxxxx
> > > > 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@xxxxxxxxxx> wrote:
> > > >  
> > > > > Add check before assigning chip->ecc.read_page() and
> > > > > chip->ecc.write_page()
> > > > >
> > > > > Signed-off-by: Naga Sureshkumar Relli
> > > > > <naga.sureshkumar.relli@xxxxxxxxxx>
> > > > > ---
> > > > >  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.

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