linux-kernel - Re: [PATCH v4 55/58] mtd: nand: add helpers to access ->priv

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Message-ID: <20151218221758.GQ10460@google.com>
Date:	Fri, 18 Dec 2015 14:17:58 -0800
From:	Brian Norris <computersforpeace@...il.com>
To:	Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	linux-mtd@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
	Hartley Sweeten <hsweeten@...ionengravers.com>,
	Ryan Mallon <rmallon@...il.com>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <kernel@...gutronix.de>,
	Imre Kaloz <kaloz@...nwrt.org>,
	Krzysztof Halasa <khalasa@...p.pl>,
	Tony Lindgren <tony@...mide.com>, linux-omap@...r.kernel.org,
	Alexander Clouter <alex@...riz.org.uk>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Gregory CLEMENT <gregory.clement@...e-electrons.com>,
	Jason Cooper <jason@...edaemon.net>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	Andrew Lunn <andrew@...n.ch>, Daniel Mack <daniel@...que.org>,
	Haojian Zhuang <haojian.zhuang@...il.com>,
	Robert Jarzmik <robert.jarzmik@...e.fr>,
	Marek Vasut <marek.vasut@...il.com>,
	Steven Miao <realmz6@...il.com>,
	adi-buildroot-devel@...ts.sourceforge.net,
	Mikael Starvik <starvik@...s.com>,
	Jesper Nilsson <jesper.nilsson@...s.com>,
	linux-cris-kernel@...s.com, Josh Wu <josh.wu@...el.com>,
	Wan ZongShun <mcuos.com@...il.com>,
	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	Maxim Levitsky <maximlevitsky@...il.com>,
	Kukjin Kim <kgene@...nel.org>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	linux-samsung-soc@...r.kernel.org,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Chen-Yu Tsai <wens@...e.org>, linux-sunxi@...glegroups.com,
	Stefan Agner <stefan@...er.ch>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	devel@...verdev.osuosl.org
Subject: Re: [PATCH v4 55/58] mtd: nand: add helpers to access ->priv

Hi Boris,

On Thu, Dec 10, 2015 at 09:00:39AM +0100, Boris Brezillon wrote:
> Add two helpers to access the field reserved for private controller data.
> This makes it clearer what this field is reserved for and ease future
> refactoring.

I agree with the refactoring part, but I'm not sure about the name. Is
it really "controller" data? That sounds like something that has 1
instance per controller. But the way this is sometimes used, we get 1
instance per NAND chip, and there may be more than one NAND chip per
controller.

So at the moment, this is more like opaque "driver data", like
dev_{get,set}_drvdata(), which doesn't really have a prescribed use --
it's up to the driver.

Notably, we already have a (sort of) 1-per-controler-instance field:
struct nand_hw_control (I notice we have both the 'controller' and
'hwcontrol' fields in nand_chip; that's pretty ugly too...). Those don't
have private data fields, but we could of course extend that if we
really want "controller" data.

Anyway, I don't feel like this question is resolved well enough to say
that we should go change all drivers to use these accessors. I know you
have bigger plans for putting more "controller" infrastructure into the
core drivers/mtd/nand/ code, so I'd like to see how that fits in here.

(If we're going to discuss this much more, I'd suggest a smaller CC
list. I'm mostly putting this here to show why I'm not taking the last
4 patches right now.)

Regards,
Brian

> Signed-off-by: Boris Brezillon <boris.brezillon@...e-electrons.com>
> ---
>  include/linux/mtd/nand.h | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/include/linux/mtd/nand.h b/include/linux/mtd/nand.h
> index 2bee2e4..4aed4b2 100644
> --- a/include/linux/mtd/nand.h
> +++ b/include/linux/mtd/nand.h
> @@ -739,6 +739,16 @@ static inline struct mtd_info *nand_to_mtd(struct nand_chip *chip)
>  	return &chip->mtd;
>  }
>  
> +static inline void *nand_get_controller_data(struct nand_chip *chip)
> +{
> +	return chip->priv;
> +}
> +
> +static inline void nand_set_controller_data(struct nand_chip *chip, void *priv)
> +{
> +	chip->priv = priv;
> +}
> +
>  /*
>   * NAND Flash Manufacturer ID Codes
>   */
> -- 
> 2.1.4
> 
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