linux-kernel - Re: [PATCH v5 2/5] driver core: Functional dependencies tracking support

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Date:   Thu, 10 Nov 2016 09:46:42 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Lukas Wunner <lukas@...ner.de>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM list <linux-pm@...r.kernel.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Mark Brown <broonie@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Grant Likely <grant.likely@...retlab.ca>,
        Mauro Carvalho Chehab <mchehab@....samsung.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Andrzej Hajda <a.hajda@...sung.com>
Subject: Re: [PATCH v5 2/5] driver core: Functional dependencies tracking support

On Thu, Nov 10, 2016 at 1:59 AM, Luis R. Rodriguez <mcgrof@...nel.org> wrote:
> On Wed, Nov 9, 2016 at 4:43 PM, Rafael J. Wysocki <rafael@...nel.org> wrote:
>> On Mon, Nov 7, 2016 at 10:22 PM, Luis R. Rodriguez <mcgrof@...nel.org> wrote:
>>> As clarified by Rafael at Plumbers, this functional dependencies
>>> framework assumes your driver / subsystem supports deferred probe,
>>
>> It isn't particularly clear what you mean by "support" here.
>
> I noted some folks had reported issues, and you acknowledged that if
> deferred probe was used in some drivers and if this created an issue
> the same issue would be seen with this framework. AFAICT there are two
> possible issues to consider:
>
> 1) the one Geert Uytterhoeven noted. Again I'll note what he had mentioned [0].
>
>   "Some drivers / subsystems don’t support deferred probe yet, such failures
>    usually don’t blow up, but cause subtle malfunctioning. Example, an Ethernet
>    phy could not get its interrupt as the primary IRQ chip had not been probed
>    yet, it reverted to polling though. Sub-optimal." [0]
>
> [0] https://lists.linuxfoundation.org/pipermail/ksummit-discuss/2016-August/003425.html
>
> Geert can you provide more details?

Issue reported in "of_mdiobus_register_phy() and deferred probe"
(http://lkml.iu.edu/hypermail/linux/kernel/1510.2/05770.html)

Key point is:
"However, of_mdiobus_register_phy() uses irq_of_parse_and_map(), which plainly
 ignores EPROBE_DEFER, and it just continues."

At that time, the PHY driver fell back to polling, but as of commit d5c3d8465
("net: phy: Avoid polling PHY with PHY_IGNORE_INTERRUPTS") that's no longer the
case, and now the PHY fails to work completely.

Workaround is "[PATCH v2] irqchip/renesas-irqc: Postpone driver initialization"
(https://www.spinics.net/lists/netdev/msg403325.html), which seems to have
sparked some interest in fixing the issue for good ;-)

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