linux-kernel - Re: [PATCH v4 08/11] mtd: brcmnand: add BCM63138 support

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Date:	Wed, 13 May 2015 12:45:21 -0700
From:	Brian Norris <computersforpeace@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-mtd@...ts.infradead.org, Dmitry Torokhov <dtor@...gle.com>,
	Anatol Pomazao <anatol@...gle.com>,
	Ray Jui <rjui@...adcom.com>,
	Corneliu Doban <cdoban@...adcom.com>,
	Jonathan Richardson <jonathar@...adcom.com>,
	Scott Branden <sbranden@...adcom.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Rafał Miłecki <zajec5@...il.com>,
	bcm-kernel-feedback-list@...adcom.com,
	Dan Ehrenberg <dehrenberg@...omium.org>,
	Gregory Fong <gregory.0xf0@...il.com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	Kevin Cernekee <cernekee@...il.com>
Subject: Re: [PATCH v4 08/11] mtd: brcmnand: add BCM63138 support

On Wed, May 13, 2015 at 12:49:01PM +0200, Arnd Bergmann wrote:
> On Tuesday 12 May 2015 17:53:41 Brian Norris wrote:
> > +static bool bcm63138_nand_intc_ack(struct brcmnand_soc *soc)
> > +{
> > +       struct bcm63138_nand_soc_priv *priv = soc->priv;
> > +       void __iomem *mmio = priv->base + BCM63138_NAND_INT_STATUS;
> > +       u32 val = brcmnand_readl(mmio);
> > +
> > +       if (val & BCM63138_CTLRDY) {
> > +               brcmnand_writel(val & ~BCM63138_CTLRDY, mmio);
> > +               return true;
> > +       }
> > +
> > +       return false;
> > +}
> ...
> > +static int bcm63138_nand_probe(struct platform_device *pdev)
> > +{
> > +       struct device *dev = &pdev->dev;
> > +       struct bcm63138_nand_soc_priv *priv;
> > +       struct brcmnand_soc *soc;
> > +       struct resource *res;
> > +
> > +       soc = devm_kzalloc(dev, sizeof(*soc), GFP_KERNEL);
> > +       if (!soc)
> > +               return -ENOMEM;
> > +
> > +       priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> > +       if (!priv)
> > +               return -ENOMEM;
> > +
> 
> This is a slightly unconventional method of doing the abstraction.
> For consistency with a lot of other drivers, I'd do it like this:
> 
> struct bcm63138_controller {
> 	void __iomem *base;
> 	brcmnand_controller parent;
> };

Does it really make sense to publicize all of the brcmnand_controller
details to each of the constituent drivers? I was intentionally keeping
them private, with a very small and well-defined interface provided for
shim SoC drivers.

This is kind of a problem that has plagued the wider MTD (and esp. NAND)
subsystem in general; we expose a ton of details to low-level drivers,
and they're free to muck with things however they want, as long as it
ends up working. I'd rather be more intentional in what I expose.

> static bool bcm63138_nand_intc_ack(struct brcmnand_controller *parent)
> {
> 	struct bcm63138_controller *controller;
> 	controller = container_of(parent, struct brcmnand_controller, parent);
> 
> 	...
> }
> 
> static int bcm63138_nand_probe(...)
> {
> 	struct bcm63138_controller *controller;
> 
> 	controller = devm_kzalloc(dev, sizeof(*controller), GFP_KERNEL);
> 	...
> 	return brcmnand_probe(pdev, &controller->parent);
> }
> 
> This also simplifies the probe() functions and means less pointer chasing.

I could still avoid one pointer chase and one extra memory allocation by
embedding 'struct brcmnand_soc' in a 'struct bcm63138_nand_soc'. e.g.:

struct bcm63138_nand_soc {
	void __iomem *base;
	struct brcmnand_soc soc;
};

static bool bcm63138_nand_intc_ack(struct brcmnand_soc *soc)
{
	struct bcm63138_nand_soc *priv;
	priv = container_of(soc, struct bcm63138_nand_soc, soc);

	...
}

static int bcm63138_nand_probe(...)
{
	struct bcm63138_nand_soc *priv;

	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
	...
	return brcmnand_probe(pdev, &priv->soc);
}

Brian
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