linux-kernel - Re: [PATCH v4 1/2] drivers: bus: simple-pm-bus: Add support for probing simple bus only devices

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Date:   Tue, 5 Oct 2021 17:07:01 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Russell King <linux@...linux.org.uk>,
        Neil Armstrong <narmstrong@...libre.com>,
        Magnus Damm <magnus.damm@...il.com>,
        Tony Lindgren <tony@...mide.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Damien Le Moal <damien.lemoal@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-oxnas@...ups.io,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        "open list:TI ETHERNET SWITCH DRIVER (CPSW)" 
        <linux-omap@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH v4 1/2] drivers: bus: simple-pm-bus: Add support for
 probing simple bus only devices

On Wed, Sep 29, 2021 at 2:07 AM Saravana Kannan <saravanak@...gle.com> wrote:
> fw_devlink could end up creating device links for bus only devices.
> However, bus only devices don't get probed and can block probe() or
> sync_state() [1] call backs of other devices. To avoid this, probe these
> devices using the simple-pm-bus driver.
>
> However, there are instances of devices that are not simple buses (they get
> probed by their specific drivers) that also list the "simple-bus" (or other
> bus only compatible strings) in their compatible property to automatically
> populate their child devices. We still want these devices to get probed by
> their specific drivers. So, we make sure this driver only probes devices
> that are only buses.
>
> [1] - https://lore.kernel.org/lkml/CAPDyKFo9Bxremkb1dDrr4OcXSpE0keVze94Cm=zrkOVxHHxBmQ@mail.gmail.com/
> Fixes: c442a0d18744 ("driver core: Set fw_devlink to "permissive" behavior by default")
> Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> Tested-by: Saravana Kannan <saravanak@...gle.com>
> Tested-by: Ulf Hansson <ulf.hansson@...aro.org>

Works fine on R-Car Gen/Gen3 (simple-bus), and SH-Mobile AG5
and R-Mobile APE6 (simple-pm-bus).
Tested-by: Geert Uytterhoeven <geert+renesas@...der.be>

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