linux-kernel - Re: [PATCH v6 2/6] mfd: syscon: add a DT property to set value width

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Message-ID: <20151125220239.GB3627@localhost>
Date:	Wed, 25 Nov 2015 17:02:39 -0500
From:	Damien Riegel <damien.riegel@...oirfairelinux.com>
To:	Rob Herring <robh@...nel.org>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-watchdog@...r.kernel.org, devicetree@...r.kernel.org,
	Lee Jones <lee.jones@...aro.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <kernel@...gutronix.de>,
	Arnd Bergmann <arnd@...db.de>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Wim Van Sebroeck <wim@...ana.be>,
	Guenter Roeck <linux@...ck-us.net>, kernel@...oirfairelinux.com
Subject: Re: [PATCH v6 2/6] mfd: syscon: add a DT property to set value width

On Wed, Nov 25, 2015 at 02:32:53PM -0600, Rob Herring wrote:
> On Wed, Nov 25, 2015 at 02:25:03PM -0500, Damien Riegel wrote:
> > Currently syscon has a fixed configuration of 32 bits for register and
> > values widths. In some cases, it would be desirable to be able to
> > customize the value width.
> > 
> > For example, certain boards (like the ones manufactured by Technologic
> > Systems) have a FPGA that is memory-mapped, but its registers are only
> > 16-bit wide.
> > 
> > This patch adds an optional "bus-width" DT binding for syscon that
> > allows to change the width for the data bus (i.e. val_bits). If this
> > property is provided, it will also adjust the register stride to
> > bus-width / 8. If not provided, the default configuration is used.
> 
> See the 8250 UART bindings. This problem is already solved and has 
> standard bindings for it.

Okay, I'll change bus-width to reg-io-width. Are you also suggesting to
use reg-shift to parametrize reg_stride?

> Rob
> 
> > 
> > Signed-off-by: Damien Riegel <damien.riegel@...oirfairelinux.com>
> > Acked-by: Arnd Bergmann <arnd@...db.de>
> > Acked-by: Lee Jones <lee.jones@...aro.org>
> > ---
> >  Documentation/devicetree/bindings/mfd/syscon.txt |  3 +++
> >  drivers/mfd/syscon.c                             | 13 +++++++++++++
> >  2 files changed, 16 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/mfd/syscon.txt b/Documentation/devicetree/bindings/mfd/syscon.txt
> > index fe8150b..4c9d187 100644
> > --- a/Documentation/devicetree/bindings/mfd/syscon.txt
> > +++ b/Documentation/devicetree/bindings/mfd/syscon.txt
> > @@ -13,6 +13,9 @@ Required properties:
> >  - compatible: Should contain "syscon".
> >  - reg: the register region can be accessed from syscon
> >  
> > +Optional property:
> > +- bus-width: width of the data bus. Can be <8>, <16>, <32>, or <64>.
> > +
> >  Examples:
> >  gpr: iomuxc-gpr@...e0000 {
> >  	compatible = "fsl,imx6q-iomuxc-gpr", "syscon";
> > diff --git a/drivers/mfd/syscon.c b/drivers/mfd/syscon.c
> > index 176bf0f..5a93d80 100644
> > --- a/drivers/mfd/syscon.c
> > +++ b/drivers/mfd/syscon.c
> > @@ -47,6 +47,7 @@ static struct syscon *of_syscon_register(struct device_node *np)
> >  	struct syscon *syscon;
> >  	struct regmap *regmap;
> >  	void __iomem *base;
> > +	u32 bus_width;
> >  	int ret;
> >  	struct regmap_config syscon_config = syscon_regmap_config;
> >  
> > @@ -69,6 +70,18 @@ static struct syscon *of_syscon_register(struct device_node *np)
> >  	 else if (of_property_read_bool(np, "little-endian"))
> >  		syscon_config.val_format_endian = REGMAP_ENDIAN_LITTLE;
> >  
> > +	/*
> > +	 * search for bus-width property in DT. If it is not provided, default
> > +	 * to 32-bit. regmap_init_mmio will return an error if syscon_config's
> > +	 * values are invalid so there is no need to check them here.
> > +	 */
> > +	ret = of_property_read_u32(np, "bus-width", &bus_width);
> > +	if (ret)
> > +		bus_width = 32;
> > +
> > +	syscon_config.val_bits = bus_width;
> > +	syscon_config.reg_stride = syscon_config.val_bits / 8;
> > +
> >  	regmap = regmap_init_mmio(NULL, base, &syscon_config);
> >  	if (IS_ERR(regmap)) {
> >  		pr_err("regmap init failed\n");
> > -- 
> > 2.5.0
> > 
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