[U-Boot] [PATCH 5/5] NAND: DaVinci: allow forced disable of subpage writes

[Tom Rini <trini@ti.com>]

On Wed, Feb 12, 2014 at 06:00:22PM -0600, Scott Wood wrote:
> 
> On Tue, 2014-01-28 at 23:19 +0000, Karicheri, Muralidharan wrote:
> > >-----Original Message-----
> > >From: Scott Wood [mailto:scottwood at freescale.com]
> > >Sent: Wednesday, January 22, 2014 3:48 PM
> > >To: Karicheri, Muralidharan
> > >Cc: u-boot at lists.denx.de; Rini, Tom; Andrianov, Vitaly
> > >Subject: Re: [U-Boot] [PATCH 5/5] NAND: DaVinci: allow forced disable of subpage writes
> > >
> > >On Mon, 2014-01-20 at 17:10 -0500, Murali Karicheri wrote:
> > >> This patch introduces a configurable mechanism to disable subpage
> > >> writes in the DaVinci NAND driver.
> > >>
> > >> Signed-off-by: Vitaly Andrianov <vitalya@ti.com>
> > >> Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
> > >> ---
> > >>  drivers/mtd/nand/davinci_nand.c |    3 +++
> > >>  1 file changed, 3 insertions(+)
> > >>
> > >> diff --git a/drivers/mtd/nand/davinci_nand.c
> > >> b/drivers/mtd/nand/davinci_nand.c index 5b17d7b..75b03a7 100644
> > >> --- a/drivers/mtd/nand/davinci_nand.c
> > >> +++ b/drivers/mtd/nand/davinci_nand.c
> > >> @@ -609,6 +609,9 @@ void davinci_nand_init(struct nand_chip *nand)
> > >> #ifdef CONFIG_SYS_NAND_USE_FLASH_BBT
> > >>  	nand->bbt_options	  |= NAND_BBT_USE_FLASH;
> > >>  #endif
> > >> +#ifdef CONFIG_SYS_NAND_NO_SUBPAGE_WRITE
> > >> +	nand->options	  |= NAND_NO_SUBPAGE_WRITE;
> > >> +#endif
> > >>  #ifdef CONFIG_SYS_NAND_HW_ECC
> > >>  	nand->ecc.mode = NAND_ECC_HW;
> > >>  	nand->ecc.size = 512;
> > >
> > >Why does it need to be configurable?
> > >
> > 
> > Same driver used in multiple platforms, and on some platforms like the one
> > I work with doesn't support subpage writes and has to be disabled.
> 
> The option needs to be documented, and it should be either named in a
> davinci-specific manner, or the documentation should clearly list which
> drivers pay attention to it.

Agreed.

> It seems odd though, that the ability to support subpage writes is an
> independent thing rather than a consequence of some other variable such
> as controller version.

I suspect this is similar to the OMAP driver where we could support
subpages but it gets tricky coordinating with the HW ECC engine for BCH8
and higher.  Perhaps there are davinci targets with smaller ECC levels
where it works out OK but keystone is doing BCH8 or 16 and it's not
worth the savings.

-- 
Tom
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