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Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.5.0 MIME-Version: 1.0 In-Reply-To: <20190226232822.GA174696@google.com> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190227_020223_666039_76425D63 X-CRM114-Status: GOOD ( 29.76 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Ganapathi Bhat , Jeffy Chen , Heiko Stuebner , devicetree@vger.kernel.org, Xinming Hu , netdev@vger.kernel.org, linux-pm@vger.kernel.org, linux-wireless@vger.kernel.org, linux-kernel@vger.kernel.org, Amitkumar Karwar , linux-rockchip@lists.infradead.org, Nishant Sarmukadam , Rob Herring , "Rafael J. Wysocki" , linux-arm-kernel@lists.infradead.org, Enric Balletbo i Serra , Lorenzo Pieralisi , "David S. Miller" , Kalle Valo , Tony Lindgren Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org + Lorenzo Hi Brian, On 26/02/2019 23:28, Brian Norris wrote: > + others > > Hi Marc, > > Thanks for the series. I have a few bits of history to add to this, and > some comments. > > On Sun, Feb 24, 2019 at 02:04:22PM +0000, Marc Zyngier wrote: >> For quite some time, I wondered why the PCI mwifiex device built in my >> Chromebook was unable to use the good old legacy interrupts. But as MSIs >> were working fine, I never really bothered investigating. I finally had a >> look, and the result isn't very pretty. >> >> On this machine (rk3399-based kevin), the wake-up interrupt is described as >> such: >> >> &pci_rootport { >> mvl_wifi: wifi@0,0 { >> compatible = "pci1b4b,2b42"; >> reg = <0x83010000 0x0 0x00000000 0x0 0x00100000 >> 0x83010000 0x0 0x00100000 0x0 0x00100000>; >> interrupt-parent = <&gpio0>; >> interrupts = <8 IRQ_TYPE_LEVEL_LOW>; >> pinctrl-names = "default"; >> pinctrl-0 = <&wlan_host_wake_l>; >> wakeup-source; >> }; >> }; >> >> Note how the interrupt is part of the properties directly attached to the >> PCI node. And yet, this interrupt has nothing to do with a PCI legacy >> interrupt, as it is attached to the wake-up widget that bypasses the PCIe RC >> altogether (Yay for the broken design!). This is in total violation of the >> IEEE Std 1275-1994 spec[1], which clearly documents that such interrupt >> specifiers describe the PCI device interrupts, and must obey the >> INT-{A,B,C,D} mapping. Oops! > > You're not the first person to notice this. All the motivations are not > necessarily painted clearly in their cover letter, but here are some > previous attempts at solving this problem: > > [RFC PATCH v11 0/5] PCI: rockchip: Move PCIe WAKE# handling into pci core > https://lkml.kernel.org/lkml/20171225114742.18920-1-jeffy.chen@rock-chips.com/ > http://lkml.kernel.org/lkml/20171226023646.17722-1-jeffy.chen@rock-chips.com/ > > As you can see by the 12th iteration, it wasn't left unsolved for lack > of trying... I wasn't aware of this. That's definitely a better approach than my hack, and I would really like this to be revived. > > Frankly, if a proper DT replacement to the admittedly bad binding isn't > agreed upon quickly, I'd be very happy to just have WAKE# support > removed from the DTS for now, and the existing mwifiex binding should > just be removed. (Wake-on-WiFi was never properly vetted on these > platforms anyway.) It mostly serves to just cause problems like you've > noticed. Agreed. If there is no actual use for this, and that we can build a case for a better solution, let's remove the wakeup support from the Gru DT (it is invalid anyway), and bring it back if and when we get the right level of support. [...] > One problem Rockchip authors were also trying to resolve here is that > PCIe WAKE# handling should not really be something the PCI device driver > has to handle directly. Despite your complaints about not using in-band > TLP wakeup, a separate WAKE# pin is in fact a documented part of the > PCIe standard, and it so happens that the Rockchip RC does not support > handling TLPs in S3, if you want to have decent power consumption. (Your > "bad hardware" complaints could justifiably fall here, I suppose.) > > Additionally, I've had pushback from PCI driver authors/maintainers on > adding more special handling for this sort of interrupt property (not > the binding specifically, but just the concept of handling WAKE# in the > driver), as they claim this should be handled by the system firmware, > when they set the appropriate wakeup flags, which filter down to > __pci_enable_wake() -> platform_pci_set_wakeup(). That's how x86 systems > do it (note: I know for a fact that many have a very similar > architecture -- WAKE# is not routed to the RC, because, why does it need > to? and they *don't* use TLP wakeup either -- they just hide it in > firmware better), and it Just Works. Even on an arm64 platform, there is no reason why a wakeup interrupt couldn't be handled by FW rather than the OS. It just need to be wired to the right spot (so that it generates a secure interrupt that can be handled by FW). > So, we basically concluded that we should standardize on a way to > describe WAKE# interrupts such that PCI drivers don't have to deal with > it at all, and the PCI core can do it for us. 12 revisions later > and...we still never agreed on a good device tree binding for this. Is the DT binding the only problem? Do we have an agreement for the core code? > IOW, maybe your wake-up sub-node is the best way to side-step the > problems of conflicting with the OF PCI spec. But I'd still really like > to avoid parsing it in mwifiex, if at all possible. Honestly, my solution is just a terrible hack. I wasn't aware that this was a more general problem, and I'd love it to be addressed in the core PCI code. > (We'd still be left with the marvell,wakeup-pin propery to parse > specifically in mwifiex, which sadly has to exist because....well, > Samsung decided to do chip-on-board, and then they failed to use the > correct pin on Marvell's side when wiring up WAKE#. Sigh.) Oh well... Thanks, M. -- Jazz is not dead. It just smells funny... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel