Re: [PATCH] mtd: nand: omap2: Fix subpage write

[Boris Brezillon <boris.brezillon@free-electrons.com>]

On Thu, 19 Oct 2017 17:11:34 +0300
Roger Quadros <rogerq@ti.com> wrote:

> On 19/10/17 16:51, Boris Brezillon wrote:
> > On Thu, 19 Oct 2017 11:41:29 +0300
> > Roger Quadros <rogerq@ti.com> wrote:
> >   
> >> Since v4.12, NAND subpage writes were causing a NULL pointer
> >> dereference on OMAP platforms (omap2-nand) using OMAP_ECC_BCH4_CODE_HW,
> >> OMAP_ECC_BCH8_CODE_HW and OMAP_ECC_BCH16_CODE_HW.
> >>
> >> This is because for those ECC modes, omap_calculate_ecc_bch()
> >> generates ECC bytes for the entire (multi-sector) page and this can
> >> overflow the ECC buffer provided by nand_write_subpage_hwecc()
> >> as it expects ecc.calculate() to return ECC bytes for just one sector.
> >>
> >> However, the root cause of the problem is present much before
> >> v4.12 but was not seen then as NAND buffers were being allocated
> >> as one big chunck prior to
> >> commit 3deb9979c731 ("mtd: nand: allocate aligned buffers if NAND_OWN_BUFFERS is unset")
> >>
> >> Fix the issue by providing a OMAP optimized write_subpage() implementation.
> >>
> >> cc: <stable@vger.kernel.org> # v4.12+
> >> Signed-off-by: Roger Quadros <rogerq@ti.com>
> >> ---
> >>  drivers/mtd/nand/omap2.c | 338 +++++++++++++++++++++++++++++++----------------
> >>  1 file changed, 225 insertions(+), 113 deletions(-)
> >>
> >> diff --git a/drivers/mtd/nand/omap2.c b/drivers/mtd/nand/omap2.c
> >> index 54540c8..a0bd456 100644
> >> --- a/drivers/mtd/nand/omap2.c
> >> +++ b/drivers/mtd/nand/omap2.c
> >> @@ -1133,129 +1133,172 @@ static u8  bch8_polynomial[] = {0xef, 0x51, 0x2e, 0x09, 0xed, 0x93, 0x9a, 0xc2,
> >>  				0x97, 0x79, 0xe5, 0x24, 0xb5};
> >>    
> 
> <snip>
> 
> >> +
> >> +/**
> >>   * omap_read_page_bch - BCH ecc based page read function for entire page
> >>   * @mtd:		mtd info structure
> >>   * @chip:		nand chip info structure
> >> @@ -2044,7 +2153,7 @@ static int omap_nand_probe(struct platform_device *pdev)
> >>  		nand_chip->ecc.strength		= 4;
> >>  		nand_chip->ecc.hwctl		= omap_enable_hwecc_bch;
> >>  		nand_chip->ecc.correct		= nand_bch_correct_data;
> >> -		nand_chip->ecc.calculate	= omap_calculate_ecc_bch;
> >> +		nand_chip->ecc.calculate	= omap_calculate_ecc_bch_sw;
> >>  		mtd_set_ooblayout(mtd, &omap_sw_ooblayout_ops);
> >>  		/* Reserve one byte for the OMAP marker */
> >>  		oobbytes_per_step		= nand_chip->ecc.bytes + 1;
> >> @@ -2066,9 +2175,10 @@ static int omap_nand_probe(struct platform_device *pdev)
> >>  		nand_chip->ecc.strength		= 4;
> >>  		nand_chip->ecc.hwctl		= omap_enable_hwecc_bch;
> >>  		nand_chip->ecc.correct		= omap_elm_correct_data;
> >> -		nand_chip->ecc.calculate	= omap_calculate_ecc_bch;
> >> +		nand_chip->ecc.calculate	= omap_calculate_ecc_bch_multi;
> >>  		nand_chip->ecc.read_page	= omap_read_page_bch;
> >>  		nand_chip->ecc.write_page	= omap_write_page_bch;
> >> +		nand_chip->ecc.write_subpage	= omap_write_subpage_bch;
> >>  		mtd_set_ooblayout(mtd, &omap_ooblayout_ops);
> >>  		oobbytes_per_step		= nand_chip->ecc.bytes;
> >>  
> >> @@ -2087,7 +2197,7 @@ static int omap_nand_probe(struct platform_device *pdev)
> >>  		nand_chip->ecc.strength		= 8;
> >>  		nand_chip->ecc.hwctl		= omap_enable_hwecc_bch;
> >>  		nand_chip->ecc.correct		= nand_bch_correct_data;
> >> -		nand_chip->ecc.calculate	= omap_calculate_ecc_bch;
> >> +		nand_chip->ecc.calculate	= omap_calculate_ecc_bch_sw;
> >>  		mtd_set_ooblayout(mtd, &omap_sw_ooblayout_ops);
> >>  		/* Reserve one byte for the OMAP marker */
> >>  		oobbytes_per_step		= nand_chip->ecc.bytes + 1;
> >> @@ -2109,9 +2219,10 @@ static int omap_nand_probe(struct platform_device *pdev)
> >>  		nand_chip->ecc.strength		= 8;
> >>  		nand_chip->ecc.hwctl		= omap_enable_hwecc_bch;
> >>  		nand_chip->ecc.correct		= omap_elm_correct_data;
> >> -		nand_chip->ecc.calculate	= omap_calculate_ecc_bch;
> >> +		nand_chip->ecc.calculate	= omap_calculate_ecc_bch_multi;  
> > 
> > Hm, it still looks wrong. omap_calculate_ecc_bch_multi() will generate
> > the same overflow when called by the core, or am I missing something?
> >   
> In the current setup core will never call ecc.calculate as we're overriding every op
> that can be used.

Do you have a custom ->read_subpage()? If you don't, the core will use
nand_read_subpage(), and it's calling ->calculate() internally.

> 
> The thing is that omap driver code uses these hooks as is so I wasn't sure
> if I should change the caller code to call the multi versions directly and fix these
> hooks to single sector versions.

I'd prefer this solution.

> 
> Alternatively, is it OK to set them to NULL?

Hm, I'm pretty sure it's not, see my comment about ->read_subpage().

> 
> 
> >>  		nand_chip->ecc.read_page	= omap_read_page_bch;
> >>  		nand_chip->ecc.write_page	= omap_write_page_bch;
> >> +		nand_chip->ecc.write_subpage	= omap_write_subpage_bch;
> >>  		mtd_set_ooblayout(mtd, &omap_ooblayout_ops);
> >>  		oobbytes_per_step		= nand_chip->ecc.bytes;
> >>  
> >> @@ -2131,9 +2242,10 @@ static int omap_nand_probe(struct platform_device *pdev)
> >>  		nand_chip->ecc.strength		= 16;
> >>  		nand_chip->ecc.hwctl		= omap_enable_hwecc_bch;
> >>  		nand_chip->ecc.correct		= omap_elm_correct_data;
> >> -		nand_chip->ecc.calculate	= omap_calculate_ecc_bch;
> >> +		nand_chip->ecc.calculate	= omap_calculate_ecc_bch_multi;
> >>  		nand_chip->ecc.read_page	= omap_read_page_bch;
> >>  		nand_chip->ecc.write_page	= omap_write_page_bch;
> >> +		nand_chip->ecc.write_subpage	= omap_write_subpage_bch;
> >>  		mtd_set_ooblayout(mtd, &omap_ooblayout_ops);
> >>  		oobbytes_per_step		= nand_chip->ecc.bytes;
> >>    
> >   
>