linux-kernel - Re: [PATCH] pinctrl: samsung: Allow grouping multiple pinmux/pinconf nodes

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Date:	Tue, 19 Nov 2013 12:10:01 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Tomasz Figa <t.figa@...sung.com>,
	linux-arm-kernel@...ts.infradead.org
CC:	linux-samsung-soc@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Linus Walleij <linus.walleij@...aro.org>,
	Doug Anderson <dianders@...omium.org>,
	Thomas Abraham <thomas.abraham@...aro.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Heiko Stübner <heiko@...ech.de>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH] pinctrl: samsung: Allow grouping multiple pinmux/pinconf
 nodes

On 11/19/2013 10:10 AM, Tomasz Figa wrote:
> One of remaining limitations of current pinctrl-samsung driver was
> the inability to parse multiple pinmux/pinconf group nodes grouped
> inside a single device tree node. It made defining groups of pins for
> single purpose, but with different parameters very inconvenient.
> 
> This patch implements Tegra-like support for grouping multiple pinctrl
> groups inside one device tree node, by completely changing the way
> pin groups and functions are parsed from device tree.

> The code creating
> pinctrl maps from DT nodes has been borrowed from pinctrl-tegra,

A lot of the Tegra code has been slightly generalized and put into
pinconf-generic.c. Can the Samsung driver be converted to use that core
code rather than adding another copy of it? Perhaps this isn't possible
given the backwards-compatibility requirements that allow either 1- or
2-level nodes though, although I imagine that could be added to the core
code. One thing you'd certainly need to do is enhance the code in
pinconf-generic.c so that you could substitute your own
pinconf_generic_parse_dt_config() function or dt_params[] table, to
allow for the SoC-specific property names, but I doubt that's too hard.
Tegra could be converted then too:-)

> while
> the initial creation of groups and functions has been completely
> rewritten with following assumptions:
>  - each group consists of just one pin and does not depend on data
>    from device tree,
>  - each function is represented by a device tree child node of the
>    pin controller, which in turn can contain multiple child nodes
>    for pins that need to have different configuration values.

OK, I think that sounds reasonable.

> Device Tree bindings are fully backwards compatible. New functionality
> can be used by defining a new pinctrl group consisting of several child
> nodes, as on following example:
> 
> 	sd4_bus8: sd4-bus-width8 {
> 		part-1 {
> 			samsung,pins = "gpk0-3", "gpk0-4",
> 					"gpk0-5", "gpk0-6";
> 			samsung,pin-function = <3>;
> 			samsung,pin-pud = <3>;
> 			samsung,pin-drv = <3>;
> 		};
> 		part-2 {
> 			samsung,pins = "gpk1-3", "gpk1-4",
> 					"gpk1-5", "gpk1-6";
> 			samsung,pin-function = <4>;
> 			samsung,pin-pud = <4>;
> 			samsung,pin-drv = <3>;
> 		};
> 	};

OK, that all looks great!

> diff --git a/Documentation/devicetree/bindings/pinctrl/samsung-pinctrl.txt b/Documentation/devicetree/bindings/pinctrl/samsung-pinctrl.txt

The DT changes fully, and the code a little briefly,
Reviewed-by: Stephen Warren <swarren@...dia.com>

Just a minor comment below,

> diff --git a/drivers/pinctrl/pinctrl-samsung.c b/drivers/pinctrl/pinctrl-samsung.c

> +static int samsung_pinctrl_create_function(struct device *dev,
> +				struct samsung_pinctrl_drv_data *drvdata,
> +				struct device_node *func_np,
> +				struct samsung_pmx_func *func)
...
> +	for (i = 0; i < npins; ++i) {
> +		const char *gname;
> +		char *gname_copy;
> +
> +		ret = of_property_read_string_index(func_np, "samsung,pins",
> +							i, &gname);
> +		if (ret) {
> +			dev_err(dev,
> +				"failed to read pin name %d from %s node\n",
> +				i, func_np->name);
> +			return ret;
>  		}
> +
> +		gname_copy = devm_kzalloc(dev, strlen(gname) + 1, GFP_KERNEL);
> +		if (!gname_copy)
> +			return -ENOMEM;
> +		strcpy(gname_copy, gname);

Is the lifetime of the string "returned" by
of_property_read_string_index() really so short that you must copy the
string? I'd be tempted just to store the pointer, although perhaps you
need to get() the node so that's safe.
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