linux-kernel - Re: [GIT PULL] On-demand device probing

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Date:	Tue, 20 Oct 2015 08:47:21 +0900
From:	Alexandre Courbot <gnurou@...il.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	David Woodhouse <dwmw2@...radead.org>,
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Subject: Re: [GIT PULL] On-demand device probing

On Tue, Oct 20, 2015 at 3:39 AM, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:
> On Mon, Oct 19, 2015 at 08:27:44PM +0200, Uwe Kleine-König wrote:
>> Hello,
>>
>> On Mon, Oct 19, 2015 at 04:43:24PM +0100, Russell King - ARM Linux wrote:
>> > It's a bit ironic that you've chosen GPIO as an example there.  The
>> > "new" GPIO API (the gpiod_* stuff) only has a fwnode way to get the
>> > gpio descriptor.  There's no of_* method.
>>
>> Without following all that fwnode discussion:
>> gpiod_get et al. should work for you here, doesn't it? It just takes a
>> struct device * and I'm happy with it.
>
> What if you don't have a struct device?  I had that problem recently
> when modifying the mvebu PCIe code.  The 'struct device' node doesn't
> contain the GPIOs, it's the PCIe controller.  Individual ports on the
> controller are described in DT as sub-nodes, and the sub-nodes can
> have a GPIO for card reset purposes.  These sub-nodes don't have a
> struct device.
>
> Right now, I'm having to do this to work around this issue:
>
>         reset_gpio = of_get_named_gpio_flags(child, "reset-gpios", 0, &flags);
>         if (reset_gpio == -EPROBE_DEFER) {
>                 ret = reset_gpio;
>                 goto err;
>         }
>
>         if (gpio_is_valid(reset_gpio)) {
>                 unsigned long gpio_flags;
>
>                 port->reset_name = devm_kasprintf(dev, GFP_KERNEL, "%s-reset",
>                                                   port->name);
>                 if (!port->reset_name) {
>                         ret = -ENOMEM;
>                         goto err;
>                 }
>
>                 if (flags & OF_GPIO_ACTIVE_LOW) {
>                         dev_info(dev, "%s: reset gpio is active low\n",
>                                  of_node_full_name(child));
>                         gpio_flags = GPIOF_ACTIVE_LOW |
>                                      GPIOF_OUT_INIT_LOW;
>                 } else {
>                         gpio_flags = GPIOF_OUT_INIT_HIGH;
>                 }
>
>                 ret = devm_gpio_request_one(dev, reset_gpio, gpio_flags,
>                                             port->reset_name);
>                 if (ret) {
>                         if (ret == -EPROBE_DEFER)
>                                 goto err;
>                         goto skip;
>                 }
>
>                 port->reset_gpio = gpio_to_desc(reset_gpio);
>         }
>
> Not nice, is it?  Not nice to have that in lots of drivers either.
>
> However, switching to use any of_* or fwnode_* thing also carries with
> it another problem: you can't control the name appearing in the
> allocation, so you end up with a bunch of GPIOs requested with a "reset"
> name - meaning you lose any identification of which port the GPIO was
> bound to.

There are a few holes in the gpiod API. I see two solutions here:

1) extend devm_get_gpiod_from_child() to take an optional name argument
2) add a function to explicitly change a GPIO's name

2) seems to be the most generic solution, would that do the trick?

(sorry for the off-topic)
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