[U-Boot] [PATCH v7 02/19] nand: mxc: Add support for i.MX5

[Benoît Thébaudeau]

Hi Fabio,

On Tuesday, February 26, 2013 6:03:56 PM, Fabio Estevam wrote:
> On Tue, Feb 26, 2013 at 1:49 PM, Benoît Thébaudeau
> <benoit.thebaudeau at advansee.com> wrote:
> > Hi Fabio,
> >
> > On Tuesday, February 26, 2013 5:35:28 PM, Fabio Estevam wrote:
> >> On Tue, Feb 26, 2013 at 1:08 PM, Benoît Thébaudeau
> >> <benoit.thebaudeau at advansee.com> wrote:
> >>
> >> > This boot pin / fuse config has been used by this driver for all i.MX
> >> > platforms
> >> > from the beginning. I don't think that we really need one more software
> >> > config
> >> > here. This is hardware stuff, and the i.MX provides a dedicated hardware
> >> > configuration for it, so I think that we should use it, even if it's
> >> > made
> >> > for
> >> > NAND boot, since it's just describing the present hardware, just like DT
> >> > would.
> >> >
> >> > In the particular case of the mx53ard, there is a DIP switch that you
> >> > can
> >> > use to
> >> > fix this config to 8-bit NAND Flash. But if you have blown the fuses to
> >> > override
> >> > the boot pin config, then of course we're doomed because a wrong NAND
> >> > Flash
> >> > config has been blow.
> >>
> >> The boot config jumpers are correctly set to boot from MMC card and
> >> this is what I am using as the boot media.
> >
> > OK, then we don't have a choice.
> >
> >> Why should we decide the NAND width via boot pins if I am not booting
> >> from NAND at all?
> >>
> >> I see that current mxc nand drivers are doing like this, but I don't
> >> think this makes sense if we use NAND and does not boot from it.
> >
> > If the NAND boot config for bus width is not used by the actuel boot config
> > to
> > mean something else (which is not your case), then it's a handy way of
> > describing the NAND hardware setup without involving software. But anyway
> > we're
> > not in this case, so we need a software config.
> >
> >> I agree with this comment from tt01.h:
> >>
> >> "/*
> >>  * it's not 16 bit:
> >>  * #define CONFIG_SYS_NAND_BUSWIDTH_16BIT
> >>  *    the current u-boot mxc_nand.c tries to auto-detect, but this only
> >>  *    reads the boot settings during reset (which might be wrong)
> >>  */"
> >>
> >> and we can also see the a workaround at board/davedenx/qong/qong.c in
> >> order to tell the nand bus width is 8 bits:
> >>
> >> void qong_nand_plat_init(void *chip)
> >> {
> >>       struct nand_chip *nand = (struct nand_chip *)chip;
> >>       nand->chip_delay = 20;
> >>       nand->select_chip = qong_nand_select_chip;
> >>       nand->options &= ~NAND_BUSWIDTH_16;
> >>       board_nand_setup();
> >> }
> >
> > OK, then let's use something like CONFIG_SYS_NAND_BUSWIDTH_16BIT for all
> > boards
> > with mxc_nand enabled.
> 
> Documentation/devicetree/bindings/mtd/nand.txt  says:
> 
> nand-bus-width : 8 or 16 bus width if not present 8
> 
> I think we could do the same here, ie, if
> CONFIG_SYS_NAND_BUSWIDTH_16BIT is not defined in the board file, then
> assume it is 8-bit nand.

I 100% agree. This should make your patch quite lite.

> I can send this as a separate patch.

OK, thanks.

Best regards,
Benoît