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

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Date:   Mon, 1 Feb 2021 11:54:38 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Saravana Kannan <saravanak@...gle.com>
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

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.

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?

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.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds