linux-kernel - Re: [PATCH] clk: Mark fwnodes when their clock provider is added

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Date:   Mon, 29 Mar 2021 16:28:20 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Stephen Boyd <sboyd@...nel.org>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Jonathan Corbet <corbet@....net>,
        Frank Rowand <frowand.list@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Kevin Hilman <khilman@...nel.org>,
        Len Brown <len.brown@...el.com>, Len Brown <lenb@...nel.org>,
        Marc Zyngier <maz@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Pavel Machek <pavel@....cz>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>,
        DOCUMENTATION <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS <devicetre
        e@...r.kernel.org>, ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Android Kernel Team <kernel-team@...roid.com>, linux-rpi-kernel" 
        <linux-rpi-kernel@...ts.infradead.org>
Subject: Re: [PATCH] clk: Mark fwnodes when their clock provider is added

On Mon, Mar 29, 2021 at 2:25 PM Stephen Boyd <sboyd@...nel.org> wrote:
>
> Quoting Geert Uytterhoeven (2021-03-26 11:29:55)
> > On Fri, Mar 26, 2021 at 7:13 PM Stephen Boyd <sboyd@...nel.org> wrote:
> > > Quoting Nicolas Saenz Julienne (2021-03-25 11:25:24)
> > > > >
> > > > > This patch mainly revealed that clk/bcm/clk-raspberrypi.c driver calls
> > > > > devm_of_clk_add_hw_provider(), with a device pointer, which has a NULL
> > > > > dev->of_node. I'm not sure if adding a check for a NULL np in
> > > > > of_clk_add_hw_provider() is a right fix, though.
> > > >
> > > > I believe the right fix is not to call 'devm_of_clk_add_hw_provider()' if
> > > > 'pdev->dev.of_node == NULL'. In such case, which is RPi3's, only the CPU clock
> > > > is used, and it's defined and queried later through
> > > > devm_clk_hw_register_clkdev().
> > > >
> > > > @Marek, I don't mind taking care of it if it's OK with you.
> > > >
> > >
> > > Ah I see this is related to the patch I just reviewed. Can you reference
> > > this in the commit text? And instead of putting the change into the clk
> > > provider let's check for NULL 'np' in of_clk_add_hw_provider() instead
> > > and return 0 if there's nothing to do. That way we don't visit this
> > > problem over and over again.
> >
> > I'm not sure the latter is what we reall want: shouldn't calling
> > *of*_clk_add_hw_provider() with a NULL np be a bug in the provider?
> >
>
> I don't have a strong opinion either way. Would it be useful if the
> function returned an error when 'np' is NULL?

I lean towards returning an error. Not a strong opinion either.

-Saravana

> I guess the caller could
> use that to figure out that it should register a clkdev. But it
> shouldn't hurt to register both a clkdev lookup and a DT provider for
> the same clk. The framework will try the DT path first and then fallback
> to a clkdev lookup otherwise, so we'll be wasting memory for clkdev but
> otherwise be fine.
>
> Really it feels like we should try to unify around a
> devm_clk_add_hw_provider() API that figures out what to do based on if
> the device has an of_node or not. That would mean implementing something
> like clkdev but for a whole provider instead of a single clk. Then this
> question of returning an error would be moot here.