linux-kernel - Re: [RESEND PATCH 2/2] pinctrl: introduce complex pin description

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Message-ID: <20150714061359.GC5161@pengutronix.de>
Date:	Tue, 14 Jul 2015 08:13:59 +0200
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Ludovic Desroches <ludovic.desroches@...el.com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-gpio@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	swarren@...dotorg.org, linus.walleij@...aro.org,
	nicolas.ferre@...el.com
Subject: Re: [RESEND PATCH 2/2] pinctrl: introduce complex pin description

On Wed, Jun 10, 2015 at 05:04:57PM +0200, Ludovic Desroches wrote:
> Using a string to describe a pin in the device tree can be not enough.
> Some controllers may need extra information to fully describe a pin. It
> concerns mainly controllers which have a per pin muxing approach which
> don't fit well the notions of groups and functions.
> Instead of using a pin name, a 32 bit value is used. The 16 least
> significant bits are used for the pin number. Other 16 bits can be used to
> store extra parameters.

In the Mediatek driver we use 'pinmux' as name for the property
containing the combined pin number / mux value defines. 'pinmux' better
describes what it is...

> +
> +	if (pctldesc->complex_pin_desc)
> +		ret = of_property_count_u32_elems(np, "pins");
> +	else
> +		ret = of_property_count_strings(np, "pins");

... and has the advantage that you don't have to pass in a
complex_pin_desc variable from the driver as the different property
name inherently carries this information. 'pins' can then stay a
property containing only strings.

>  	if (ret < 0) {
>  		ret = of_property_count_strings(np, "groups");
>  		if (ret < 0)
> @@ -297,11 +305,12 @@ int pinconf_generic_dt_subnode_to_map(struct pinctrl_dev *pctldev,
>  		if (type == PIN_MAP_TYPE_INVALID)
>  			type = PIN_MAP_TYPE_CONFIGS_GROUP;
>  		subnode_target_type = "groups";
> +		pins_prop = false;
>  	} else {
>  		if (type == PIN_MAP_TYPE_INVALID)
>  			type = PIN_MAP_TYPE_CONFIGS_PIN;
>  	}
> -	strings_count = ret;
> +	items_count = ret;
>  
>  	ret = of_property_read_string(np, "function", &function);
>  	if (ret < 0) {
> @@ -326,17 +335,31 @@ int pinconf_generic_dt_subnode_to_map(struct pinctrl_dev *pctldev,
>  	if (num_configs)
>  		reserve++;
>  
> -	reserve *= strings_count;
> +	reserve *= items_count;
>  
>  	ret = pinctrl_utils_reserve_map(pctldev, map, reserved_maps,
>  			num_maps, reserve);
>  	if (ret < 0)
>  		goto exit;
>  
> -	of_property_for_each_string(np, subnode_target_type, prop, group) {
> +	items_name = kmalloc_array(items_count, sizeof(char *), GFP_KERNEL);
> +	if (!items_name)
> +		goto exit;
> +	if (pctldesc->complex_pin_desc && pins_prop) {
> +		of_property_for_each_u32(np, subnode_target_type, prop, cur, val) {
> +			pin_id = val & PINCTRL_PIN_MASK;
> +			items_name[i++] = pctldesc->pins[pin_id].name;
> +		}

I don't like that even though pins have numbers here they are converted
to strings which the driver later has to search in a list just to
convert it back into the number. This is quite inefficient.

I guess this could be optimized later, but it would be nice to have the
pin number directly in the driver.

Sascha

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