Re: [PATCH v3] mtd/nand: don't use {read,write}_buf for 8-bit transfers

[Ezequiel Garcia <ezequiel.garcia@free-electrons.com>]

On Fri, Nov 29, 2013 at 10:04:28PM -0800, Brian Norris wrote:
> 
> Unfortunately, I realized that Uwe's patch doesn't go far enough, I
> don't think. It looks like it needs something like the following diff
> (only compile-tested).
> 
> diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
> index bd39f7b67906..1ab264457d94 100644
> --- a/drivers/mtd/nand/nand_base.c
> +++ b/drivers/mtd/nand/nand_base.c
> @@ -2933,7 +2933,7 @@ static int nand_flash_detect_onfi(struct mtd_info *mtd, struct nand_chip *chip,
>  					int *busw)
>  {
>  	struct nand_onfi_params *p = &chip->onfi_params;
> -	int i;
> +	int i, j;
>  	int val;
>  
>  	/* Try ONFI for unknown chip or LP */
> @@ -2942,18 +2942,10 @@ static int nand_flash_detect_onfi(struct mtd_info *mtd, struct nand_chip *chip,
>  		chip->read_byte(mtd) != 'F' || chip->read_byte(mtd) != 'I')
>  		return 0;
>  
> -	/*
> -	 * ONFI must be probed in 8-bit mode or with NAND_BUSWIDTH_AUTO, not
> -	 * with NAND_BUSWIDTH_16
> -	 */
> -	if (chip->options & NAND_BUSWIDTH_16) {
> -		pr_err("ONFI cannot be probed in 16-bit mode; aborting\n");
> -		return 0;
> -	}
> -
>  	chip->cmdfunc(mtd, NAND_CMD_PARAM, 0, -1);
>  	for (i = 0; i < 3; i++) {
> -		chip->read_buf(mtd, (uint8_t *)p, sizeof(*p));
> +		for (j = 0; j < sizeof(*p); j++)
> +			*(uint8_t *)p = chip->read_byte(mtd);
>  		if (onfi_crc16(ONFI_CRC_BASE, (uint8_t *)p, 254) ==
>  				le16_to_cpu(p->crc)) {
>  			break;
> 
> What do you think? (And more importantly, how does this test out for
> you?)
> 

Your proposal would work (fixing a minor typo for incrementing 'p'),
except the nand_command() implementation messes with the buswith.
Therefore, after a long debugging session, I could make it work using
this hack:

@@ -542,8 +545,8 @@ static void nand_command(struct mtd_info *mtd, unsigned int command,
 	/* Serially input address */
 	if (column != -1) {
 		/* Adjust columns for 16 bit buswidth */
-		if (chip->options & NAND_BUSWIDTH_16)
-			column >>= 1;
+//		if (chip->options & NAND_BUSWIDTH_16)
+//			column >>= 1;
 		chip->cmd_ctrl(mtd, column, ctrl);
 		ctrl &= ~NAND_CTRL_CHANGE;
 	}

Now, IMHO, the solution of setting the defaults to x8 during the device
detection phase, is far simpler.

BTW: this is not really related to Uwe's patch, right? It's just a complement
to his work, as far as I can see.
-- 
Ezequiel García, Free Electrons
Embedded Linux, Kernel and Android Engineering
http://free-electrons.com