Re: [PATCH v5 2/3] mtd: brcmnand: Force 8bit mode before doing nand_scan_ident()

[Brian Norris <computersforpeace@gmail.com>]

On Fri, Oct 30, 2015 at 12:29:20PM +0530, Anup Patel wrote:
> Just like other NAND controllers,

^^ That part isn't strictly true. While READ ID data only comes out on
the lower 8 bits, that doesn't *actually* mean you can't get valid data
from a 16-bit bus in general; you just have to drop the upper 8 bits. That's
what these two commits did for read ID and parameter page read commands:

commit 3dad2344e92c6e1aeae42df1c4824f307c51bcc7
Author: Brian Norris <computersforpeace@gmail.com>
Date:   Wed Jan 29 14:08:12 2014 -0800

    mtd: nand: force NAND_CMD_READID onto 8-bit bus

commit bd9c6e99b58255b9de1982711ac9487c9a2f18be
Author: Brian Norris <computersforpeace@gmail.com>
Date:   Fri Nov 29 22:04:28 2013 -0800

    mtd: nand: don't use read_buf for 8-bit ONFI transfers

> the NAND READID command only works
> in 8bit mode for all versions of BRCMNAND controller.

But I presume *this* statement is actually true. This NAND controller doesn't
exactly give us a fully-flexible READID / read_byte / read_word command, as it
works at a higher level than that (although LOW_LEVEL_OP gives us this
flexibility now). I could imagine (though I never tested 16-bit NAND) that
16-bit READID is broken.

BTW, did you ask the HW designer about this? It'd be nice to be 100% sure.

Anyway, as I noted on the cover letter, I've pushed this patch.

Thanks,
Brian

> This patch forces 8bit mode for each NAND CS in brcmnand_init_cs()
> before doing nand_scan_ident() to ensure that BRCMNAND controller
> is in 8bit mode when NAND READID command is issued.
> 
> Signed-off-by: Anup Patel <anup.patel@broadcom.com>
> Reviewed-by: Ray Jui <rjui@broadcom.com>
> Reviewed-by: Scott Branden <sbranden@broadcom.com>
> ---
>  drivers/mtd/nand/brcmnand/brcmnand.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/mtd/nand/brcmnand/brcmnand.c b/drivers/mtd/nand/brcmnand/brcmnand.c
> index dda96fa..b410527 100644
> --- a/drivers/mtd/nand/brcmnand/brcmnand.c
> +++ b/drivers/mtd/nand/brcmnand/brcmnand.c
> @@ -1912,6 +1912,7 @@ static int brcmnand_init_cs(struct brcmnand_host *host)
>  	struct mtd_info *mtd;
>  	struct nand_chip *chip;
>  	int ret;
> +	u16 cfg_offs;
>  	struct mtd_part_parser_data ppdata = { .of_node = dn };
>  
>  	ret = of_property_read_u32(dn, "reg", &host->cs);
> @@ -1954,6 +1955,15 @@ static int brcmnand_init_cs(struct brcmnand_host *host)
>  
>  	chip->controller = &ctrl->controller;
>  
> +	/*
> +	 * The bootloader might have configured 16bit mode but
> +	 * NAND READID command only works in 8bit mode. We force
> +	 * 8bit mode here to ensure that NAND READID commands works.
> +	 */
> +	cfg_offs = brcmnand_cs_offset(ctrl, host->cs, BRCMNAND_CS_CFG);
> +	nand_writereg(ctrl, cfg_offs,
> +		      nand_readreg(ctrl, cfg_offs) & ~CFG_BUS_WIDTH);
> +
>  	if (nand_scan_ident(mtd, 1, NULL))
>  		return -ENXIO;
>  
> -- 
> 1.9.1
>