From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: "Michał Kępień" <kernel@kempniu.pl>
Cc: Darren Hart <dvhart@infradead.org>,
Jonathan Woithe <jwoithe@just42.net>,
Andy Shevchenko <andy@infradead.org>,
platform-driver-x86@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 00/10] fujitsu-laptop: use device-specific data instead of module-wide globals
Date: Thu, 11 May 2017 16:37:30 +0200 [thread overview]
Message-ID: <2351586.Dq8uyyCcAZ@aspire.rjw.lan> (raw)
In-Reply-To: <20170511135211.GB1166@ozzy.nask.waw.pl>
On Thursday, May 11, 2017 03:52:11 PM Michał Kępień wrote:
> > On Tuesday, May 09, 2017 09:47:34 AM Darren Hart wrote:
> > > On Tue, May 09, 2017 at 11:35:24AM +0200, Michał Kępień wrote:
> > > > > On Sat, May 06, 2017 at 02:45:16PM +0200, Michał Kępień wrote:
> > > > > > > Just to make sure we are all on the same page here, choosing the "two
> > > > > > > separate modules, each with one driver for one ACPI device" approach
> > > > > > > would mean ending up with two modules:
> > > > > > >
> > > > > > > - fujitsu-laptop, binding to the FUJ02E3 ACPI device, handling
> > > > > > > everything _except_ backlight,
> > > > > > >
> > > > > > > - fujitsu-backlight, binding to the FUJ02B1 ACPI device, handling
> > > > > > > backlight and depending on fujitsu-laptop.
> > > > > > >
> > > > > > > We would need to export one function from fujitsu-laptop, namely
> > > > > > > fext_backlight(). I understand this would require creating a separate
> > > > > > > header file which would then be included in fujitsu-backlight.
> > > > > > >
> > > > > > > fext_backlight() causes the FUNC method of the FUJ02E3 ACPI device to be
> > > > > > > called. This method is marked as Serialized, which AFAIU means we do
> > > > > > > not need a separate lock in kernel code because all calls to this method
> > > > > > > are implicitly serialized by firmware itself.
> > > > > > >
> > > > > > > I do not see anything "unnatural" in this approach, but I would love to
> > > > > > > be corrected if I am wrong.
> > > > > >
> > > > > > To be fair, one thing that may be "unnatural" with this approach is that
> > > > > > even though fujitsu-backlight would depend on fujitsu-laptop, it would
> > > > > > still have to get a handle to FUJ02E3 using:
> > > > > >
> > > > > > acpi_get_handle(NULL, "\\_SB.FEXT", ...)
> > > > > >
> > > > > > because call_fext_func() - and thus fext_backlight() - needs to be
> > > > > > passed a handle to FUJ02E3 and the two ACPI devices (FUJ02B1 handled by
> > > > > > fujitsu-backlight and FUJ02E3 handled by fujitsu-laptop) are not related
> > > > > > from the perspective of the ACPI device hierarchy. Unless there is a
> > > > > > better way of implementing this, in which case I am open to suggestions.
> > > > >
> > > > > At a high level, I would consider the handle to be private data which should be
> > > > > encapsulated in fujitsu_laptop. Or... where is FEXT in the ACPI hierarchy
> > > > > relative to FUJ02E3?
> > > >
> > > > FEXT *is* FUJ02E3:
> > > >
> > > > Device (FEXT)
> > > > {
> > > > Name (_HID, "FUJ02E3") // _HID: Hardware ID
> > > > ...
> > > > Method (FUNC, 4, Serialized)
> > > > {
> > > > ...
> > > > }
> > > > ...
> > > > }
> > > >
> > > > See also below.
> > > >
> > > > > Assuming FEXT is below FUJ02E3, the we appear to be making an assumption that
> > > > > there is only one FUJ02E3 on the system. While I think this is perfectly
> > > > > reasonable, it does contradict the argumentation from some of the other patches
> > > > > in this series.
> > > >
> > > > Exactly. The whole purpose of this patch series is to stop using
> > > > module-wide data. We have a different situation here than in the case
> > > > of e.g. dell-smbios, which coordinates access to a module-wide buffer it
> > > > allocates.
> > > >
> > > > > If FEXT is not below fujitsu laptop... then it is a shared function which either
> > > > > one of them can own and serialize (or not if fw indeed handles that).
> > > > >
> > > > > Either way, the owning driver should abstract away the private data and present
> > > > > an interface the other can use with only the "public" information.
> > > >
> > > > I feel the problem at hand needs a fresh explanation. I will be as
> > > > concise as possible.
> > > >
> > > > We are considering two ACPI devices present on Fujitsu laptops:
> > > >
> > > > - FJEX:
> > > > * path: \_SB_.PCI0.LPCB.FJEX
> > > > * HID: FUJ02B1
> > > > * methods invoked by kernel: GBLL, RBLL, SBLL, SBL2
> > > > * handles: backlight level (LCD brightness)
> > > >
> > > > - FEXT:
> > > > * path: \_SB_.FEXT
> > > > * HID: FUJ02E3
> > > > * methods invoked by kernel: FUNC
> > > > * handles: hotkey, LEDs, platform attributes, backlight power
> > > > ^^^^^^^^^^^^^^^
> > >
> > > This is very concise and describes the problem clearly, thank you!
> > >
> > > >
> > > > The problem is that if we split the ACPI drivers for those two devices
> > > > into separate modules, the FJEX driver will need to access the FUNC
> > > > method of device FEXT, handled by another driver in another module.
> > > >
> > > > One way of solving this cleanly is to store a handle to the most
> > > > recently found FEXT instance (there should always be at most one anyway)
> > > > in a module-wide variable inside the FEXT driver, but that defeats the
> > > > purpose of this series.
> > > >
> > > > Another solution is proposed by patch 04/10 of this series: make the
> > > > FJEX driver independently grab a handle to FEXT using the absolute ACPI
> > > > path to the latter. It feels unnatural (AFAICT only one driver outside
> > > > drivers/acpi, namely pcc-cpufreq, does that), but it is safe and allows
> > > > us to drop all module-wide data.
> > >
> > > Rafael's take on this would be useful.
> >
> > Well, can you point me to patch [04/10] then?
>
> Here is a link:
>
> https://www.spinics.net/lists/platform-driver-x86/msg11412.html
Thanks!
> However, please note that in light of what Darren wrote, this specific
> patch is likely to be dropped from v2. Thus, there may be no point in
> reviewing it after all, though your feedback would certainly be
> appreciated for future reference.
OK
> > Or better resend the whole series with a CC to linux-acpi (which it should go
> > to to start with IMO).
>
> I did not think of that as this ten-patch series mostly revolves around
> data encapsulation. However, I think it might be worthwhile to CC
> linux-acpi for the series that will split fujitsu-laptop in two, shall
> it ever be posted.
OK, but as a rule of thumb, it is better to CC everything touching ACPI to
linux-acpi just to let people know what you're doing if nothing else.
And if there are ACPI-related questions down the road, the context is there
aleady, so it is generally easier to answer them then.
Thanks,
Rafael
next prev parent reply other threads:[~2017-05-11 14:44 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-24 13:33 [PATCH 00/10] fujitsu-laptop: use device-specific data instead of module-wide globals Michał Kępień
2017-04-24 13:33 ` [PATCH 01/10] platform/x86: fujitsu-laptop: introduce fext_*() helper functions Michał Kępień
2017-05-01 13:13 ` Jonathan Woithe
2017-05-02 13:24 ` Michał Kępień
2017-04-24 13:33 ` [PATCH 02/10] platform/x86: fujitsu-laptop: shorten names of acpi_handle fields Michał Kępień
2017-05-01 13:19 ` Jonathan Woithe
2017-05-01 16:09 ` Darren Hart
2017-04-24 13:33 ` [PATCH 03/10] platform/x86: fujitsu-laptop: explicitly pass ACPI handle to call_fext_func() Michał Kępień
2017-04-24 13:33 ` [PATCH 04/10] platform/x86: fujitsu-laptop: rework backlight power synchronization Michał Kępień
2017-05-01 13:32 ` Jonathan Woithe
2017-05-01 16:17 ` Darren Hart
2017-04-24 13:33 ` [PATCH 05/10] platform/x86: fujitsu-laptop: distinguish current uses of device-specific data Michał Kępień
2017-05-01 13:40 ` Jonathan Woithe
2017-04-24 13:33 ` [PATCH 06/10] platform/x86: fujitsu-laptop: allocate struct fujitsu_bl in acpi_fujitsu_bl_add() Michał Kępień
2017-04-24 13:33 ` [PATCH 07/10] platform/x86: fujitsu-laptop: use device-specific data in backlight code Michał Kępień
2017-04-24 13:33 ` [PATCH 08/10] platform/x86: fujitsu-laptop: allocate struct fujitsu_laptop in acpi_fujitsu_laptop_add() Michał Kępień
2017-04-24 13:33 ` [PATCH 09/10] platform/x86: fujitsu-laptop: use device-specific data in LED-related code Michał Kępień
2017-04-24 13:33 ` [PATCH 10/10] platform/x86: fujitsu-laptop: use device-specific data in remaining module code Michał Kępień
2017-05-01 13:05 ` [PATCH 00/10] fujitsu-laptop: use device-specific data instead of module-wide globals Jonathan Woithe
2017-05-02 13:21 ` Michał Kępień
2017-05-04 23:40 ` Jonathan Woithe
2017-05-05 16:15 ` Darren Hart
2017-05-06 12:31 ` Michał Kępień
2017-05-06 12:45 ` Michał Kępień
2017-05-06 14:21 ` Andy Shevchenko
2017-05-06 14:23 ` Andy Shevchenko
2017-05-08 16:01 ` Darren Hart
2017-05-09 9:35 ` Michał Kępień
2017-05-09 12:13 ` Jonathan Woithe
2017-05-09 16:47 ` Darren Hart
2017-05-09 21:24 ` Rafael J. Wysocki
2017-05-11 13:52 ` Michał Kępień
2017-05-11 14:37 ` Rafael J. Wysocki [this message]
2017-05-11 15:38 ` Darren Hart
2017-05-11 13:40 ` Michał Kępień
2017-05-15 23:27 ` Darren Hart
2017-05-16 0:06 ` Jonathan Woithe
2017-05-16 6:40 ` Michał Kępień
2017-05-15 23:56 ` Jonathan Woithe
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