linux-kernel - Re: [PATCH v3 5/9] mtd: nand: add sunxi NAND flash controller support

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Date:	Tue, 20 May 2014 11:49:42 -0700
From:	Brian Norris <computersforpeace@...il.com>
To:	Boris BREZILLON <b.brezillon.dev@...il.com>
Cc:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	Emilio López <emilio@...pez.com.ar>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Rob Herring <robherring2@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Grant Likely <grant.likely@...aro.org>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Arnd Bergmann <arnd@...db.de>, devicetree@...r.kernel.org,
	linux-doc@...r.kernel.org, dev@...ux-sunxi.org,
	linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 5/9] mtd: nand: add sunxi NAND flash controller support

On Fri, May 09, 2014 at 06:47:22PM +0200, Boris BREZILLON wrote:
> On 09/05/2014 18:03, Ezequiel Garcia wrote:
> > On 12 Mar 07:07 PM, Boris BREZILLON wrote:
> >> --- /dev/null
> >> +++ b/drivers/mtd/nand/sunxi_nand.c
> >> @@ -0,0 +1,1276 @@
...
> >> +static int sunxi_nand_ecc_init(struct mtd_info *mtd, struct nand_ecc_ctrl *ecc,
> >> +			       struct device_node *np)
> >> +{
> >> +	struct nand_chip *nand = mtd->priv;
> >> +	int ecc_step_size, ecc_strength;
> >> +	int ret;
> >> +
> >> +	ecc_step_size = of_get_nand_ecc_step_size(np);
> >> +	ecc_strength = of_get_nand_ecc_strength(np);
> >> +	if (ecc_step_size > 0 && ecc_strength > 0) {
> >> +		ecc->size = ecc_step_size;
> >> +		ecc->strength = ecc_strength;
> >> +	} else {
> >> +		ecc->size = nand->ecc_step_ds;
> >> +		ecc->strength = nand->ecc_strength_ds;
> >> +	}
> >> +
> > Shouldn't you check the devicetree value is not weaker than the ONFI-obtained?
> 
> I can definitely do that.

You can do that here, but take a look at the discussion Ezequiel and I
had about this:

  http://thread.gmane.org/gmane.linux.drivers.devicetree/67462

We probably don't want to be doing anything drastic like overriding the
device tree configuration. Instead, we might want to stick a warning
into the core nand_base code that does the proper comparison of the
'*_ds' values with the actual values chosen in
chip->ecc->{size,strength}. The comparison is kind of subtle, actually,
so it'd be good to do it exactly once for everyone.

Brian
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