[U-Boot] [RFC/PATCH 1/4] Enable multi chip support in the NAND layer

[Stefan Roese <sr@denx.de>]

Hi Wolfgang,

On Monday 19 January 2009, Wolfgang Grandegger wrote:
> >> Are they accessed as 2 NAND controllers, or 2 chips on one controller?
> >
> > 2 chips on one controller.
> >
> >> We can make it "#define NAND_MAX_CHIPS 2" if that's appropriate, but
> >> defining it to CONFIG_SYS_MAX_NAND_DEVICE doesn't seem to make sense.
> >
> > OK with me.
>
> NAND_MAX_CHIPS should be set to 1!
>
> NAND_MAX_CHIPS defines the number of NAND chips (or dies) *per* NAND
> device (or bank) meaning two or more identical NAND chips can be mapped
> to one device. So far this was not supported, because nand_scan() was
> always called with maxchips=1 in nand_init_chip:
>
> $ cat drivers/mtd/nand/nand.c:
> ...
> static void nand_init_chip(struct mtd_info *mtd, struct nand_chip *nand,
>                            ulong base_addr)
> {
>         mtd->priv = nand;
>
>         nand->IO_ADDR_R = nand->IO_ADDR_W = (void  __iomem *)base_addr;
>         if (board_nand_init(nand) == 0) {
>                 if (nand_scan(mtd, 1) == 0) {
>                     ^^^^^^^^^^^^^^^^^
>                         if (!mtd->name)
>                                 mtd->name = (char *)default_nand_name;
>                 } else
>                         mtd->name = NULL;
>         } else {
>                 mtd->name = NULL;
>                 mtd->size = 0;
>         }
> }
>
> Furthermore, the callback chip->select_chip() must be provided by the
> NAND driver to select the chips properly. It's seems not to be
> implemented for NDFC and therefore you do not have this choice.
> Therefore NAND_MAX_CHIPS should be set to 1 for the Bamboo.

The 4xx NDFC driver uses the board_nand_select_device() function to select the 
NAND chip (other platforms do it this way as well). IIRC, this function was 
already introduced with old legacy NAND driver. Could be that it is 
deprecated now and should be replaced with the ->select_device() function.

Best regards,
Stefan

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