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

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Date:   Mon, 9 Nov 2020 10:53:05 -0800
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Lukasz Stelmach <l.stelmach@...sung.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.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

On Mon, Nov 09, 2020 at 07:18:37PM +0100, Lukasz Stelmach wrote:
> 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.

Yeah, I disagree with Andy here. The lookup tables are a crutch that we
have until GPIO and PWM a taught to support software nodes (I need to
resurrect my patch series for GPIO, if you have time to test that would
be awesome).

Thanks.

-- 
Dmitry