From: Tomeu Vizoso <tomeu.vizoso@collabora.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: "Mark Brown" <broonie@kernel.org>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Rob Herring" <robh+dt@kernel.org>,
"Michael Turquette" <mturquette@baylibre.com>,
"Stephen Boyd" <sboyd@codeaurora.org>,
"Vinod Koul" <vinod.koul@intel.com>,
"Dan Williams" <dan.j.williams@intel.com>,
"Linus Walleij" <linus.walleij@linaro.org>,
"Alexandre Courbot" <gnurou@gmail.com>,
"Thierry Reding" <thierry.reding@gmail.com>,
"David Airlie" <airlied@linux.ie>,
"Terje Bergström" <tbergstrom@nvidia.com>,
"Stephen Warren" <swarren@wwwdotorg.org>,
"Wolfram Sang" <wsa@the-dreams.de>,
"Frank Rowand" <frowand.list@gmail.com>,
"Grant Likely" <grant.likely@linaro.org>,
"Kishon Vijay Abraham I" <kishon@ti.com>,
"Sebastian Reichel" <sre@kernel.org>,
"Dmitry Eremin-Solenikov" <dbaryshkov@gmail.com>,
"David Woodhouse" <dwmw2@infradead.org>,
"Liam Girdwood" <lgirdwood@gmail.com>,
"Felipe Balbi" <balbi@ti.com>
Subject: Re: [GIT PULL] On-demand device probing
Date: Mon, 19 Oct 2015 17:00:54 +0200 [thread overview]
Message-ID: <CAAObsKDWM6A98tdKHqi4fe5DBf0BmB0JeghcZDWan_PYbyshag@mail.gmail.com> (raw)
In-Reply-To: <20151019143045.GE32532@n2100.arm.linux.org.uk>
On 19 October 2015 at 16:30, Russell King - ARM Linux
<linux@arm.linux.org.uk> wrote:
> On Mon, Oct 19, 2015 at 04:10:56PM +0200, Tomeu Vizoso wrote:
>> On 19 October 2015 at 15:18, Russell King - ARM Linux
>> <linux@arm.linux.org.uk> wrote:
>> > On Mon, Oct 19, 2015 at 02:34:22PM +0200, Tomeu Vizoso wrote:
>> >> ... If a device is available and has
>> >> a compatible driver, but it cannot be probed because a dependency
>> >> isn't going to be available, that's an error and is going to cause
>> >> real-world problems unless the device is redundant. Currently we say
>> >> nothing because with deferred probe the probe callbacks are also part
>> >> of the mechanism that determines the dependency order.
>> >
>> > So what if device X depends on device Y, and we have a driver for
>> > device Y built-in to the kernel, but the driver for device X is a
>> > module?
>> >
>> > I don't see this being solvable in the way you describe above - it's
>> > going to identify X as being unable to be satisfied, and report it as
>> > an error - but it's not an error at all.
>>
>> It's going to probe Y at late_initcall, then probe X when its driver
>> is registered. No deferred probes nor messages about it.
>>
>> But if you meant to write the opposite case (X built-in and Y in a
>> module), then I have to ask you in what situation that would make
>> sense.
>
> I did mean the opposite way around. It may not make sense if you're
> targetting a single platform, but it may make sense in a single zImage
> kernel.
>
> Consider something like a single zImage kernel that is built with
> everything built-in to be able to boot and mount rootfs without
> initramfs support on both platform A and platform B. Both platforms
> share some hardware (eg, an I2C GPIO expander) which is built as a
> module. It is a resource provider. Platform B contains a driver
> which is required to boot on platform A, but not platform B (so the
> kernel has to have that driver built-in.) On platform B, there is
> a dependency to the I2C GPIO expander device.
I see, in this situation the person trying to find out why some device
hadn't probed would enable debug logging of failed probes and would
see one spurious message if there was a deferred probe because of the
module.
>> >> Having a specific switch for enabling deferred probe logging sounds
>> >> good, but there's going to be hundreds of spurious messages about
>> >> deferred probes that were just deferrals and only one of them is going
>> >> to be the actual error in which a device failed to find a dependency.
>> >
>> > Why would there be? Sounds like something's very wrong there.
>>
>> Sorry about that, I have checked that only now and I "only" get 39
>> deferred probe messages on exynos5250-snow.
>
> I typically see one or two, maybe five maximum on the platforms I have
> here, but normally zero.
Hmm, I have given a look at our lava farm and have seen 2 dozens as
common (with multi_v7).
>> > So, really, after boot and all appropriate modules have been loaded,
>> > you should end up with no deferred probes. Are you saying that you
>> > still have "hundreds" at that point? If you do, that sounds like
>> > there's something very wrong.
>>
>> I was talking about messages if we log each -EPROBE_DEFER, not devices
>> that remain to be probed. The point being that right now we don't have
>> a way to know if we are deferring because the dependency will be
>> around later, or if we have a problem and the dependency isn't going
>> to be there at all.
>
> What's the difference between a dependency which isn't around because
> the driver is not built into the kernel but is available as a module,
> and a dependency that isn't around because the module hasn't been
> loaded yet?
>
> How do you distinguish between those two scenarios? In the former
> scenario, the device will eventually come up when udev loads the
> module. In the latter case, it's a persistent failing case.
Agreed, but it's something that doesn't happen often and that's why
such messages would be at the debug level instead of being warns or
errors.
>> Agreed, with the note from above on why it would be better to only
>> print such a message only when the -EPROBE_DEFER is likely to be a
>> problem.
>
> ... and my argument is that there's _no way_ to know for certain which
> deferred probes will be a problem, and which won't. The only way to
> definitely know that is if you disable kernel modules, and require
> all drivers to be built into the kernel.
>
> What you can do is print those devices which have failed to probe at
> late_initcall() time - possibly augmenting that with reports from
> subsystems showing what resources are not available, but that's only
> a guide, because of the "it might or might not be in a kernel module"
> problem.
Well, adding those reports would give you a changelog similar to the
one in this series...
Thanks,
Tomeu
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next prev parent reply other threads:[~2015-10-19 15:00 UTC|newest]
Thread overview: 102+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-14 8:34 [GIT PULL] On-demand device probing Tomeu Vizoso
2015-10-14 9:26 ` Mark Brown
2015-10-15 11:42 ` Tomeu Vizoso
[not found] ` <1444909328-24761-1-git-send-email-tomeu.vizoso-ZGY8ohtN/8qB+jHODAdFcQ@public.gmane.org>
2015-10-16 21:23 ` Olof Johansson
2015-10-17 15:19 ` Rob Herring
2015-10-19 16:52 ` Olof Johansson
2015-10-17 6:57 ` Greg Kroah-Hartman
2015-10-17 15:04 ` Rob Herring
2015-10-17 15:47 ` Greg Kroah-Hartman
2015-10-17 16:28 ` Rob Herring
2015-10-17 16:56 ` Greg Kroah-Hartman
2015-10-17 17:54 ` Rob Clark
2015-10-17 18:27 ` Greg Kroah-Hartman
2015-10-17 18:45 ` Rob Clark
2015-10-17 18:59 ` Greg Kroah-Hartman
2015-10-17 19:39 ` Rob Clark
2015-10-17 20:22 ` Greg Kroah-Hartman
2015-10-17 19:04 ` Noralf Trønnes
2015-10-17 19:48 ` Rob Clark
2015-10-18 19:41 ` Mark Brown
2015-10-18 19:29 ` Mark Brown
2015-10-18 19:37 ` Greg Kroah-Hartman
2015-10-18 19:53 ` Mark Brown
2015-10-19 9:44 ` David Woodhouse
2015-10-19 9:52 ` Russell King - ARM Linux
2015-10-19 11:02 ` Mark Brown
2015-10-19 12:35 ` Rob Herring
2015-10-19 12:47 ` David Woodhouse
2015-10-19 14:50 ` Mark Brown
2015-10-19 15:29 ` David Woodhouse
2015-10-19 15:43 ` Russell King - ARM Linux
2015-10-19 18:27 ` Uwe Kleine-König
2015-10-19 18:39 ` Russell King - ARM Linux
2015-10-19 23:47 ` Alexandre Courbot
2015-10-20 11:12 ` David Woodhouse
2015-10-19 15:58 ` Rob Herring
2015-10-19 21:40 ` Rafael J. Wysocki
2015-10-19 22:58 ` Rob Herring
[not found] ` <CAL_JsqKa3MFJUWKV2KxPE_NmrP2g4dOD3zr+0Kyx4yBkDOg2HA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-10-20 7:56 ` Rafael J. Wysocki
2015-10-20 14:15 ` Rob Herring
[not found] ` <CAL_JsqJuu5_Osqi+X6M6UeRDZFQB+_8riYDF1gvsGayk5-4SFw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-10-20 14:40 ` Alan Stern
2015-10-20 15:36 ` Mark Brown
2015-10-20 16:04 ` Alan Stern
2015-10-20 16:21 ` Tomeu Vizoso
2015-10-20 17:14 ` Alan Stern
2015-10-20 19:35 ` Mark Brown
2015-10-20 23:35 ` Rafael J. Wysocki
2015-10-21 6:15 ` Jean-Francois Moine
2015-10-22 0:54 ` Rafael J. Wysocki
2015-10-22 9:14 ` Tomeu Vizoso
2015-10-27 5:03 ` Rafael J. Wysocki
2015-10-20 23:34 ` Rafael J. Wysocki
2015-10-21 8:55 ` Geert Uytterhoeven
2015-10-21 23:39 ` Rafael J. Wysocki
2015-10-19 16:04 ` Mark Brown
2015-10-19 12:34 ` Tomeu Vizoso
2015-10-19 13:18 ` Russell King - ARM Linux
[not found] ` <20151019131821.GA32532-l+eeeJia6m9vn6HldHNs0ANdhmdF6hFW@public.gmane.org>
2015-10-19 14:10 ` Tomeu Vizoso
2015-10-19 14:30 ` Russell King - ARM Linux
2015-10-19 15:00 ` Tomeu Vizoso [this message]
2015-10-19 15:35 ` Russell King - ARM Linux
2015-10-19 16:21 ` Geert Uytterhoeven
2015-10-19 16:45 ` Russell King - ARM Linux
2015-10-20 15:46 ` Alternative approach to solve the deferred probe (was: [GIT PULL] On-demand device probing) Russell King - ARM Linux
2015-10-21 3:58 ` Alternative approach to solve the deferred probe Frank Rowand
2015-10-21 8:18 ` Russell King - ARM Linux
2015-10-21 15:36 ` Frank Rowand
2015-10-21 16:55 ` Grygorii Strashko
2015-10-21 17:20 ` Russell King - ARM Linux
2015-10-21 18:13 ` Grygorii Strashko
2015-10-21 18:28 ` Russell King - ARM Linux
2015-10-22 15:12 ` Grygorii Strashko
2015-10-21 18:02 ` Frank Rowand
2015-10-21 18:29 ` Grygorii Strashko
2015-10-21 20:35 ` Russell King - ARM Linux
2015-10-22 0:05 ` Frank Rowand
2015-10-22 13:20 ` Alternative approach to solve the deferred probe (was: [GIT PULL] On-demand device probing) Mark Brown
[not found] ` <CAAObsKB2BUZ-smid45wOdAQw6h2yNqCydk+azAFNk69ewHJtZQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-10-21 15:59 ` [GIT PULL] On-demand device probing Frank Rowand
2015-10-21 16:27 ` Mark Brown
2015-10-21 18:18 ` Frank Rowand
2015-10-21 21:03 ` Mark Brown
2015-10-21 21:12 ` Rob Herring
2015-10-21 21:50 ` Frank Rowand
2015-10-22 9:05 ` Tomeu Vizoso
2015-10-22 14:38 ` Greg Kroah-Hartman
2015-10-22 14:44 ` Greg Kroah-Hartman
[not found] ` <20151022144405.GC21861-U8xfFu+wG4EAvxtiuMwx3w@public.gmane.org>
2015-10-22 15:02 ` Russell King - ARM Linux
2015-10-22 23:33 ` Mark Brown
2015-10-22 18:53 ` Frank Rowand
2015-10-22 19:26 ` Greg Kroah-Hartman
[not found] ` <20151022192639.GC27248-U8xfFu+wG4EAvxtiuMwx3w@public.gmane.org>
2015-10-23 12:28 ` Tomeu Vizoso
[not found] ` <562930AB.1070203-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2015-10-23 15:45 ` Tim Bird
2015-10-23 16:34 ` Rob Herring
2015-10-24 14:17 ` Rafael J. Wysocki
2015-10-24 22:06 ` Mark Brown
2015-10-25 13:54 ` Rafael J. Wysocki
2015-10-26 1:12 ` Mark Brown
2015-10-26 10:51 ` Michael Turquette
2015-10-26 12:55 ` Tomeu Vizoso
2015-10-26 23:37 ` Rafael J. Wysocki
2015-10-25 19:45 ` Andrew F. Davis
2015-10-24 17:55 ` Geert Uytterhoeven
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