linux-kernel - Re: [PATCH 3/3] mtd: brcmnand: respect ECC algorithm set by NAND subsystem

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Message-ID: <20160426093736.3978a718@bbrezillon>
Date:	Tue, 26 Apr 2016 09:37:36 +0200
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	Brian Norris <computersforpeace@...il.com>,
	Rafał Miłecki <zajec5@...il.com>
Cc:	linux-mtd@...ts.infradead.org, Kamal Dasu <kdasu.kdev@...il.com>,
	Richard Weinberger <richard@....at>,
	David Woodhouse <dwmw2@...radead.org>,
	"open list:BROADCOM STB NAND FLASH DRIVER" 
	<bcm-kernel-feedback-list@...adcom.com>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] mtd: brcmnand: respect ECC algorithm set by NAND
 subsystem

Hi Brian,

On Mon, 25 Apr 2016 22:53:55 -0700
Brian Norris <computersforpeace@...il.com> wrote:

> On Fri, Apr 22, 2016 at 01:23:15PM +0200, Rafał Miłecki wrote:
> > It's more reliable than guessing based on ECC strength. It allows using
> > NAND on devices with BCH-1 (e.g. D-Link DIR-885L).
> > 
> > Signed-off-by: Rafał Miłecki <zajec5@...il.com>
> > ---
> >  drivers/mtd/nand/brcmnand/brcmnand.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/mtd/nand/brcmnand/brcmnand.c b/drivers/mtd/nand/brcmnand/brcmnand.c
> > index c3331ff..dcb22dc 100644
> > --- a/drivers/mtd/nand/brcmnand/brcmnand.c
> > +++ b/drivers/mtd/nand/brcmnand/brcmnand.c
> > @@ -1927,7 +1927,7 @@ static int brcmnand_setup_dev(struct brcmnand_host *host)
> >  
> >  	switch (chip->ecc.size) {
> >  	case 512:
> > -		if (chip->ecc.strength == 1) /* Hamming */
> > +		if (chip->ecc.algo == NAND_ECC_HAMMING)  
> 
> This doesn't handle most of the problems I noted on the early version of
> this series. (But thank you for following through on the algorithm
> selection refactoring!)
> 
> Particularly, this change will
> (a) break any existing DTs which used to have 'nand-ecc-size = <1>', and
>     would assume this gets Hamming ECC; and
> (b) allows DTs to specify Hamming ECC for unsupported modes, like 1024B
>     sectors, or ecc_level != 1. None of these are supported in HW.

Indeed.

> 
> >  			cfg->ecc_level = 15;
> >  		else
> >  			cfg->ecc_level = chip->ecc.strength;  
> 
> Something like the following probably works better (not tested):
> 
> ---8<---
> 
> From: Brian Norris <computersforpeace@...il.com>
> Date: Mon, 25 Apr 2016 20:48:02 -0700
> Subject: [PATCH] mtd: brcmnand: respect ECC algorithm set by the NAND
>  subsystem
> 
> This is more obvious than guessing based on ECC strength. It allows
> using NAND on devices with BCH-1 (e.g. D-Link DIR-885L).
> 
> This maintains DT backward compatibility by defaulting to Hamming if a
> 1-bit ECC algorithm is specified without a corresponding algorithm
> selection. i.e., to use BCH-1, you must specify:
> 
>   nand-ecc-strength = <1>;
>   nand-ecc-step-size = <512>;
>   nand-ecc-algo = "bch";
> 
> Also adds a check to ensure we haven't allowed someone to get by with SW
> ECC. If we want to support SW ECC, we need to refactor some other pieces
> of this driver.

I'm waiting a bit before applying this patch (I'd like to have a
Tested-by first).

> 
> Signed-off-by: Brian Norris <computersforpeace@...il.com>
> ---
>  drivers/mtd/nand/brcmnand/brcmnand.c | 24 +++++++++++++++++++++++-
>  1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/nand/brcmnand/brcmnand.c b/drivers/mtd/nand/brcmnand/brcmnand.c
> index c3331ffcaffd..b76ad7c0144f 100644
> --- a/drivers/mtd/nand/brcmnand/brcmnand.c
> +++ b/drivers/mtd/nand/brcmnand/brcmnand.c
> @@ -1925,9 +1925,31 @@ static int brcmnand_setup_dev(struct brcmnand_host *host)
>  	cfg->col_adr_bytes = 2;
>  	cfg->blk_adr_bytes = get_blk_adr_bytes(mtd->size, mtd->writesize);
>  
> +	if (chip->ecc.mode != NAND_ECC_HW) {
> +		dev_err(ctrl->dev, "only HW ECC supported; selected: %d\n",
> +			chip->ecc.mode);
> +		return -EINVAL;
> +	}
> +
> +	if (chip->ecc.algo == NAND_ECC_UNKNOWN) {
> +		if (chip->ecc.strength == 1 && chip->ecc.size == 512)
> +			/* Default to Hamming for 1-bit ECC, if unspecified */
> +			chip->ecc.algo = NAND_ECC_HAMMING;
> +		else
> +			/* Otherwise, BCH */
> +			chip->ecc.algo = NAND_ECC_BCH;
> +	}
> +
> +	if (chip->ecc.algo == NAND_ECC_HAMMING && (chip->ecc.strength != 1 ||
> +						   chip->ecc.size != 512)) {
> +		dev_err(ctrl->dev, "invalid Hamming params: %d bits per %d bytes\n",
> +			chip->ecc.strength, chip->ecc.size);
> +		return -EINVAL;
> +	}
> +
>  	switch (chip->ecc.size) {
>  	case 512:
> -		if (chip->ecc.strength == 1) /* Hamming */
> +		if (chip->ecc.algo == NAND_ECC_HAMMING)
>  			cfg->ecc_level = 15;
>  		else
>  			cfg->ecc_level = chip->ecc.strength;



-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com