linux-kernel - Re: [PATCH v3 05/11] memory: add Atmel EBI (External Bus Interface) driver

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Message-ID: <20141201192923.6a85e52b@bbrezillon>
Date:	Mon, 1 Dec 2014 19:29:23 +0100
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Andrew Victor <linux@...im.org.za>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Lee Jones <lee.jones@...aro.org>,
	Mark Rutland <mark.rutland@....com>,
	devicetree@...r.kernel.org,
	Jean-Jacques Hiblot <jjhiblot@...phandler.com>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
	Kumar Gala <galak@...eaurora.org>
Subject: Re: [PATCH v3 05/11] memory: add Atmel EBI (External Bus Interface)
 driver

Hi Arnd,

On Mon, 01 Dec 2014 17:26:27 +0100
Arnd Bergmann <arnd@...db.de> wrote:

> On Monday 01 December 2014 11:27:21 Boris Brezillon wrote:
> > The EBI (External Bus Interface) is used to access external peripherals
> > (NOR, SRAM, NAND, and other specific devices like ethernet controllers).
> > Each device is assigned a CS line and an address range and can have its
> > own configuration (timings, access mode, bus width, ...).
> > This driver provides a generic DT binding to configure a device according
> > to its requirements.
> > For specific device controllers (like the NAND one) the SMC timings
> > should be configured by the controller driver through the matrix and
> > smc syscon regmaps.
> 
> Nice!
> 
> > +
> > +#define AT91_EBICSA_REGFIELD(soc)			\
> > +	REG_FIELD(soc ## _MATRIX_EBICSA_OFF, 0,		\
> > +		  AT91_MATRIX_EBI_NUM_CS - 1)
> > +
> > +#define AT91_MULTI_EBICSA_REGFIELD(soc, n)		\
> > +	REG_FIELD(soc ## _MATRIX_EBI ## n ## CSA_OFF,	\
> > +		  0, AT91_MATRIX_EBI_NUM_CS - 1)
> 
> I don't like the use macros that concatenate symbol names like
> this. Why not do either
> 
> - open-code the macro contents in the few uses, to allow
>   grepping for them, or

I'm not sure to get this one, are you suggesting to do something like
this:

#define AT91_EBICSA_REGFIELD(off)			\
	REG_FIELD(ebicsa_off, AT91_MATRIX_EBI_NUM_CS - 1)

> 
> - put the register number in the syscon reference and look it
>   up from there (this would be slightly more complicated for the
>   second macro)

I've told several times not to encode register offsets or register ids
in the DT :-) (and if I'm not mistaken that's what you're suggesting
here).

> 
> > +
> > +	np = of_parse_phandle(pdev->dev.of_node, "atmel,smc", 0);
> > +	if (!np)
> > +		return -EINVAL;
> > +
> > +	ebi->smc = syscon_node_to_regmap(np);
> > +	if (IS_ERR(ebi->smc))
> > +		return PTR_ERR(ebi->smc);
> 
> I think this and the second instance of it can be shortened to
> 
> 	ebi->smc = syscon_regmap_lookup_by_phandle(pdev->dev.of_node, "atmel,smc");

Sure.

Regards,

Boris


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