linux-kernel - Re: [PATCH v8 3/6] software node: implement reference properties

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Message-ID: <dleftj4klypf5u.fsf%l.stelmach@samsung.com>
Date:   Mon, 09 Nov 2020 19:18:37 +0100
From:   Lukasz Stelmach <l.stelmach@...sung.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        platform-driver-x86@...r.kernel.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH v8 3/6] software node: implement reference properties

It was <2020-11-09 pon 19:24>, when Andy Shevchenko wrote:
> On Mon, Nov 09, 2020 at 06:02:29PM +0100, Lukasz Stelmach wrote:
>> It was <2019-11-07 czw 20:22>, when Dmitry Torokhov wrote:
>> > It is possible to store references to software nodes in the same fashion as
>> > other static properties, so that users do not need to define separate
>> > structures:
>> >
>> > static const struct software_node gpio_bank_b_node = {
>> > 	.name = "B",
>> > };
>> >
>> > static const struct property_entry simone_key_enter_props[] = {
>> > 	PROPERTY_ENTRY_U32("linux,code", KEY_ENTER),
>> > 	PROPERTY_ENTRY_STRING("label", "enter"),
>> > 	PROPERTY_ENTRY_REF("gpios", &gpio_bank_b_node, 123, GPIO_ACTIVE_LOW),
>> > 	{ }
>> > };
>> >
>> > Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
>> > ---
>> 
>> I am writing a piece that needs to provide a list of gpios to a
>> diriver. The above example looks like what I need.
>
> Nope.
>
> It mustn't be used for GPIOs or PWMs or whatever that either should come via
> lookup tables or corresponding firmware interface.
>

May I ask why? I've read commit descriptions for drivers/base/swnode.c
and the discussion on lkml and I understand software nodes as a way to
provide (synthesize) a description for a device that is missing a
description in the firmware. Another use case seems to be to replace (in
the long run) platform data. That is what I am trying to use it for.

I want my device to be configured with either DT or software_nodes
created at run time with configfs. My device is going to use GPIOs
described in the DT and it is going to be configured via configfs at run
time. I could use platform_data to pass structures from configfs but
software nodes would let me save some code in the device driver and use
the same paths for both static (DT) and dynamic (configfs)
configuration.

Probably I have missed something and I will be greatful, if you tell me
where I can find more information about software nodes. There are few
users in the kernel and it isn't obvious for me how to use software
nodes properly.

>> At the moment the driver gets the list from fwnode/of_node. The list
>> contain references to phandles which get resolved and and the driver
>> ends up with a bunch of gpio descriptors. Great.
>> 
>> This example looks nice but does the code that reads the reference from
>> the gpios property and returns a gpiod actually exist? If it doesn't, I
>> am willing to write it.
>> 
>> At first glance it makes more sense to me to pass (struct gpiod_lookup
>> *) instead of (struct software_node *) and make gpiolib's gpiod_find()
>> accept lookup tables as parameter instead of searching the
>> gpio_lookup_list? Or do you think such temporary table should be
>> assembled from the above structure and then used in gpiod_find()?
>> 
>> Any other suggestions on how to get a bunch of gpios (the description
>> for gpios is available in the devicetree) for a device described with a
>> software nodes?

Kind regards,
-- 
Łukasz Stelmach
Samsung R&D Institute Poland
Samsung Electronics

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