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From: Rob Herring <robh+dt@kernel.org>
To: Saravana Kannan <saravanak@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	John Stultz <john.stultz@linaro.org>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Andrew Lunn <andrew@lunn.ch>, Vladimir Oltean <olteanv@gmail.com>,
	Android Kernel Team <kernel-team@android.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v1 1/5] driver core: fw_devlink: Improve handling of cyclic dependencies
Date: Tue, 14 Sep 2021 07:35:23 -0500	[thread overview]
Message-ID: <CAL_Jsq+FXN9cU5h7ZtcR_P6kuF-Hs3Cy-Z8rEug=F_4v0sWggg@mail.gmail.com> (raw)
In-Reply-To: <20210914043928.4066136-2-saravanak@google.com>

On Mon, Sep 13, 2021 at 11:39 PM Saravana Kannan <saravanak@google.com> wrote:
>
> When we have a dependency of the form:
>
> Device-A -> Device-C
>         Device-B
>
> Device-C -> Device-B
>
> Where,
> * Indentation denotes "child of" parent in previous line.
> * X -> Y denotes X is consumer of Y based on firmware (Eg: DT).
>
> We have cyclic dependency: device-A -> device-C -> device-B -> device-A
>
> fw_devlink current treats device-C -> device-B dependency as an invalid
> dependency and doesn't enforce it but leaves the rest of the
> dependencies as is.
>
> While the current behavior is necessary, it is not sufficient if the
> false dependency in this example is actually device-A -> device-C. When
> this is the case, device-C will correctly probe defer waiting for
> device-B to be added, but device-A will be incorrectly probe deferred by
> fw_devlink waiting on device-C to probe successfully. Due to this, none
> of the devices in the cycle will end up probing.
>
> To fix this, we need to go relax all the dependencies in the cycle like
> we already do in the other instances where fw_devlink detects cycles.
> A real world example of this was reported[1] and analyzed[2].
>
> [1] - https://lore.kernel.org/lkml/0a2c4106-7f48-2bb5-048e-8c001a7c3fda@samsung.com/
> [2] - https://lore.kernel.org/lkml/CAGETcx8peaew90SWiux=TyvuGgvTQOmO4BFALz7aj0Za5QdNFQ@mail.gmail.com/
> Fixes: f9aa460672c9 ("driver core: Refactor fw_devlink feature")
> Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Signed-off-by: Saravana Kannan <saravanak@google.com>
> ---
>  drivers/base/core.c | 17 ++++++++++++-----
>  1 file changed, 12 insertions(+), 5 deletions(-)

Am I supposed to apply this? What about the revert and mdio-parent-bus
support you mentioned? Those are needed too? Please send me a series
with what I should apply for 5.15, not fixes and new features
combined.

Rob

  parent reply	other threads:[~2021-09-14 12:35 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-14  4:39 [PATCH v1 0/5] fw_devlink improvements Saravana Kannan
2021-09-14  4:39 ` [PATCH v1 1/5] driver core: fw_devlink: Improve handling of cyclic dependencies Saravana Kannan
2021-09-14  6:16   ` Marek Szyprowski
2021-09-14  8:01     ` Saravana Kannan
2021-09-14 12:35   ` Rob Herring [this message]
2021-09-14 16:23     ` Saravana Kannan
2021-09-14  4:39 ` [PATCH v1 2/5] driver core: Set deferred probe reason when deferred by driver core Saravana Kannan
2021-09-14  7:01   ` Geert Uytterhoeven
2021-09-14  7:58     ` Saravana Kannan
2021-09-15  5:41       ` Saravana Kannan
2021-09-14  4:39 ` [PATCH v1 3/5] driver core: Create __fwnode_link_del() helper function Saravana Kannan
2021-09-14  7:04   ` Geert Uytterhoeven
2021-09-14  7:46     ` Saravana Kannan
2021-09-14  4:39 ` [PATCH v1 4/5] driver core: Add debug logs when fwnode links are added/deleted Saravana Kannan
2021-09-14  7:09   ` Geert Uytterhoeven
2021-09-14  4:39 ` [PATCH v1 5/5] driver core: Add fw_devlink.debug command line boolean parameter Saravana Kannan
2021-09-14 15:10   ` Andrew Lunn
2021-09-14 16:27     ` Saravana Kannan
2021-09-14 16:43       ` Andrew Lunn
2021-09-14 16:52         ` Rob Herring
2021-09-14 17:31           ` Saravana Kannan

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