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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Mon, 1 Feb 2021 11:31:53 +0100
Message-ID: <CAMuHMdVWJZrGDvtMiyaAOfnZP5jBJec42oQvYeZSgt9ZLhqDvA@mail.gmail.com>
Subject: Re: [PATCH v1 2/2] driver core: fw_devlink: Handle missing drivers
 for optional suppliers
To:     Saravana Kannan <saravanak@google.com>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Marc Zyngier <maz@kernel.org>,
        Tudor Ambarus <Tudor.Ambarus@microchip.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Android Kernel Team <kernel-team@android.com>
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Hi Saravana,

On Sat, Jan 30, 2021 at 5:03 AM Saravana Kannan <saravanak@google.com> wrote:
> After a deferred probe attempt has exhaused all the devices that can be
> bound, any device that remains unbound has one/both of these conditions
> true:
>
> (1) It is waiting on its supplier to bind
> (2) It does not have a matching driver
>
> So, to make fw_devlink=on more forgiving of missing drivers for optional
> suppliers, after we've done a full deferred probe attempt, this patch
> deletes all device links created by fw_devlink where the supplier hasn't
> probed yet and the supplier itself is not waiting on any of its
> suppliers. This allows consumers to probe during another deferred probe
> attempt if they were waiting on optional suppliers.
>
> When modules are enabled, we can't differentiate between a driver
> that'll never be registered vs a driver that'll be registered soon by
> loading a module. So, this patch doesn't do anything for the case where
> modules are enabled.

For the modular case, can't you do a probe regardless? Or limit it
to devices where the missing provider is a DMAC or IOMMU driver?
Many drivers can handle missing DMAC controller drivers, and are even
supposed to work that way.  They may even retry obtaining DMA releases
later.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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