linux-kernel - Re: [PATCH] Revert "mtd: davinci-nand: disable subpage write for keystone-nand"

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Message-ID: <20170329170352.2d6c0721@bbrezillon>
Date:   Wed, 29 Mar 2017 17:03:52 +0200
From:   Boris Brezillon <boris.brezillon@...e-electrons.com>
To:     Sekhar Nori <nsekhar@...com>
Cc:     Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Cyrille Pitchen <cyrille.pitchen@...el.com>,
        <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        Muralidharan Karicheri <m-karicheri2@...com>,
        Franklin S Cooper Jr <fcooper@...com>
Subject: Re: [PATCH] Revert "mtd: davinci-nand: disable subpage write for
 keystone-nand"

On Mon, 27 Mar 2017 15:56:55 +0530
Sekhar Nori <nsekhar@...com> wrote:

> This partly reverts commit 28c015a9daabe4ed3aeb0ccf669a3f1c2b8b81d5.
> 
> Since f6d7c1b5598b ("mtd: nand: davinci: Reinitialize the HW ECC
> engine in 4bit hwctl") using subpage and 4bit HWECC works.
> 
> Revert the original workaround made for this. Tested with
> mtd_subpagetest and UBIFS on K2E, K2HK, K2L EVMs.
> 
> The addition of keystone specific compatible to davinci_nand_of_match[]
> contained in original commit is retained.

Hm, it sounds like a bad idea to re-enable sub-page writes afterwards.
You might break existing systems using UBI, because UBI detects the
sub-page write feature and decides to place the VID header at a
different position depending on that.
To sum-up, you're likely to break users that have already flashed a UBI
image with the old driver.

If you want to re-enable sub-page writes, just switch back to the
"ti,davinci-nand" compatible.

> 
> Cc: Muralidharan Karicheri <m-karicheri2@...com>
> Cc: Franklin S Cooper Jr <fcooper@...com>
> Signed-off-by: Sekhar Nori <nsekhar@...com>
> ---
>  drivers/mtd/nand/davinci_nand.c | 5 -----
>  1 file changed, 5 deletions(-)
> 
> diff --git a/drivers/mtd/nand/davinci_nand.c b/drivers/mtd/nand/davinci_nand.c
> index 27fa8b87cd5f..56c4afed8d74 100644
> --- a/drivers/mtd/nand/davinci_nand.c
> +++ b/drivers/mtd/nand/davinci_nand.c
> @@ -580,11 +580,6 @@ static struct davinci_nand_pdata
>  		if (of_property_read_bool(pdev->dev.of_node,
>  			"ti,davinci-nand-use-bbt"))
>  			pdata->bbt_options = NAND_BBT_USE_FLASH;
> -
> -		if (of_device_is_compatible(pdev->dev.of_node,
> -					    "ti,keystone-nand")) {
> -			pdata->options |= NAND_NO_SUBPAGE_WRITE;
> -		}
>  	}
>  
>  	return dev_get_platdata(&pdev->dev);