From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965079AbdEKOoP convert rfc822-to-8bit (ORCPT ); Thu, 11 May 2017 10:44:15 -0400 Received: from cloudserver094114.home.net.pl ([79.96.170.134]:47538 "EHLO cloudserver094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965026AbdEKOoL (ORCPT ); Thu, 11 May 2017 10:44:11 -0400 From: "Rafael J. Wysocki" To: =?utf-8?B?TWljaGHFgiBLxJlwaWXFhA==?= Cc: Darren Hart , Jonathan Woithe , Andy Shevchenko , 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 Message-ID: <2351586.Dq8uyyCcAZ@aspire.rjw.lan> User-Agent: KMail/4.14.10 (Linux/4.11.0-rc6+; KDE/4.14.9; x86_64; ; ) In-Reply-To: <20170511135211.GB1166@ozzy.nask.waw.pl> References: <20170424133334.7064-1-kernel@kempniu.pl> <2402801.hhjSWhyBjd@aspire.rjw.lan> <20170511135211.GB1166@ozzy.nask.waw.pl> MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT Content-Type: text/plain; charset="utf-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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