Re: [PATCH v2] mtd: omap: nand: Remove 0xFF's that prefixed 16bit NAND commands

[Christopher Harvey <charvey@matrox.com>]

On Mon, Oct 29, 2012 at 02:49:03PM +0100, Ivan Djelic wrote:
> On Fri, Oct 26, 2012 at 08:36:43PM +0100, Christopher Harvey wrote:
> > In 16bit NAND mode the GPMC would send the command 0xNN as 0xFFNN
> > instead of 0x00NN on the bus. The 0xFFs were actually uninitialized
> > bits that were left unset in the GPMC command output register. The
> > reason they weren't initialized in 16bit mode is that if the same code
> > that writes to this register was used in 8bit mode then 2 commands
> > would be output in 8bit mode. One for the low byte, and an extra 0x0
> > command for the high byte. This commit uses writew if we're using
> > 16bit NAND.
> > 
> > Most chips seem fine with the extra 0xFFs, but the ONFI spec says
> > otherwise.
> 
> Hi Christopher,
> 
> Nitpick: I think you should replace 'command' with 'address' in your commit message.
> The ONFI spec says Host should send _address_ byte NN as 0x00NN. It is OK to send
> command NN as 0xFFNN, as explicitly mentioned in ONFI 3.1 spec (section 2.16):
> 
>   2.16.          Bus Width Requirements
> All NAND Targets per device shall use the same data bus width. All targets shall either have an
> 8-bit bus width or a 16-bit bus width. Note that devices that support the NV-DDR or NV-DDR2
> data interface shall have an 8-bit bus width.
> When the host supports a 16-bit bus width, only data is transferred at the 16-bit width. All
> address and command line transfers shall use only the lower 8-bits of the data bus. During
> command transfers, the host may place any value on the upper 8-bits of the data bus. During
> address transfers, the host shall set the upper 8-bits of the data bus to 00h.
> 
> Your patch deals with both command and address bytes, which does not hurt.
> BR,
> --
> Ivan

Ok, makes sense. Thanks for pointing that out. I'll update the wording.

> > 
> > Signed-off-by: Christopher Harvey <charvey@matrox.com>
> > ---
> >  drivers/mtd/nand/omap2.c |   14 +++++++++-----
> >  1 files changed, 9 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/mtd/nand/omap2.c b/drivers/mtd/nand/omap2.c
> > index 5b31386..ae6738f 100644
> > --- a/drivers/mtd/nand/omap2.c
> > +++ b/drivers/mtd/nand/omap2.c
> > @@ -225,16 +225,20 @@ static void omap_hwcontrol(struct mtd_info *mtd, int cmd, unsigned int ctrl)
> >  {
> >  	struct omap_nand_info *info = container_of(mtd,
> >  					struct omap_nand_info, mtd);
> > +	void __iomem *reg;
> >  
> >  	if (cmd != NAND_CMD_NONE) {
> >  		if (ctrl & NAND_CLE)
> > -			writeb(cmd, info->reg.gpmc_nand_command);
> > -
> > +			reg = info->reg.gpmc_nand_command;
> >  		else if (ctrl & NAND_ALE)
> > -			writeb(cmd, info->reg.gpmc_nand_address);
> > -
> > +			reg = info->reg.gpmc_nand_address;
> >  		else /* NAND_NCE */
> > -			writeb(cmd, info->reg.gpmc_nand_data);
> > +			reg = info->reg.gpmc_nand_data;
> > +
> > +		if (info->nand.options & NAND_BUSWIDTH_16)
> > +			writew(cmd, reg);
> > +		else
> > +			writeb(cmd, reg);
> >  	}
> >  }
> >  
> > -- 
> > 1.7.8.6
> >