linux-kernel - Re: [PATCH] clk: at91: sama5d2: Mark device OF

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Date:   Mon, 1 Feb 2021 09:16:32 -0800
From:   Saravana Kannan <saravanak@...gle.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Michael Turquette <mturquette@...libre.com>,
        linux-clk <linux-clk@...r.kernel.org>, mirq-linux@...e.qmqm.pl,
        Ludovic Desroches <ludovic.desroches@...rochip.com>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] clk: at91: sama5d2: Mark device OF_POPULATED after setup

On Mon, Feb 1, 2021 at 2:54 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> Hi Saravana,
>
> On Thu, Jan 28, 2021 at 6:08 PM Saravana Kannan <saravanak@...gle.com> wrote:
> > I already accounted for early clocks like this when I designed
> > fw_devlink. Each driver shouldn't need to set OF_POPULATED.
> > drivers/clk/clk.c already does this for you.
> >
> > I think the problem is that your driver is using
> > CLK_OF_DECLARE_DRIVER() instead of CLK_OF_DECLARE(). The comments for
> > CLK_OF_DECLARE_DRIVER() says:
> > /*
> >  * Use this macro when you have a driver that requires two initialization
> >  * routines, one at of_clk_init(), and one at platform device probe
> >  */
> >
> > In your case, you are explicitly NOT having a driver bind to this
> > clock later. So you shouldn't be using CLK_OF_DECLARE() instead.
>

Typo. I meant to say this driver SHOULD be using CLK_OF_DECLARE()
instead. I wonder if this is what caused you to send the email --
because we are saying the same thing.

> Unless I'm missing something, name##_of_clk_init_driver() clearing
> OF_POPULATED again causes consumer driver probing to be postponed by
> fw_devlink until the second initialization phase of the provider has been
> completed?

Right, if they use CLK_OF_DECLARE_DRIVER() what you said above will
happen and that's the issue they are trying to fix.

> This is wrong if the consumer only needs a clock instantiated during the
> first phase, and may cause issues if the consumer is a critical device.
> E.g. a timer, on ARM SoCs lacking an architecture timer (pre-Cortex
> A7/A15) or global timer (pre-Cortex A9, or single-core Cortex A9).
> Probably there are more examples.

So, needing devices like IRQ, timer and clocks early is fine.
fw_devlink can handle that correctly if the proper macros are used
(since most frameworks set the OF_POPULATED flag for these devices).

-Saravana