From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A5584EE49A0 for ; Wed, 23 Aug 2023 12:42:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234559AbjHWMmU (ORCPT ); Wed, 23 Aug 2023 08:42:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46130 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234515AbjHWMmU (ORCPT ); Wed, 23 Aug 2023 08:42:20 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 63597E46; Wed, 23 Aug 2023 05:42:18 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id E5DAA650A5; Wed, 23 Aug 2023 12:42:17 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B64AAC433C8; Wed, 23 Aug 2023 12:42:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1692794537; bh=8uzezK1wRKIpXgIyZFlOrbzbnhXdWBh2a3dmZMdQpRo=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=VWRpAmepzO+DtlYuaCJBkh8K15skd67DU6bGJvCLxJG1cfaX5G+SXYbb20zulpLkX AggySYVeZDxigKgcblRxCrKi+STjTGSymdfdQhoDBAfmWiOj/3nCa/67IgNAwNtRcP rskUJYcVSFFZy0cOMxRrXCegAjwyduZCKgh7TgYKbW0ODTSxJjyL4oR/mjtzRd0G7j B4nUgarpP/AdCbRGE1oageZ9eZo77tI+pjR74VbKtTMnAZ2Sz1Py4oIlntMpBzlp/R 0Gca63BpG1ZF6yRyI5QTpWLIS4o5TmYlYgLONr1tHedjxEHiJp2BNEuzZdw3SPhuU6 4uHQCNiHnQIBQ== Date: Wed, 23 Aug 2023 07:42:14 -0500 From: Bjorn Helgaas To: Lorenzo Pieralisi Cc: Jim Quinlan , linux-pci@vger.kernel.org, Nicolas Saenz Julienne , Bjorn Helgaas , Lorenzo Pieralisi , Cyril Brulebois , Phil Elwell , bcm-kernel-feedback-list@broadcom.com, Jim Quinlan , Florian Fainelli , Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= , Rob Herring , Krzysztof Kozlowski , Conor Dooley , "moderated list:BROADCOM BCM7XXX ARM ARCHITECTURE" , "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , open list Subject: Re: [PATCH v6 1/5] dt-bindings: PCI: brcmstb: Add brcm,enable-l1ss property Message-ID: <20230823124214.GA416689@bhelgaas> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On Wed, Aug 23, 2023 at 09:30:48AM +0200, Lorenzo Pieralisi wrote: > On Mon, Aug 21, 2023 at 12:01:50PM -0400, Jim Quinlan wrote: > > On Mon, Aug 21, 2023 at 11:41 AM Lorenzo Pieralisi > > wrote: > > > On Mon, Aug 21, 2023 at 11:25:11AM -0400, Jim Quinlan wrote: > > > > On Mon, Aug 21, 2023 at 10:47 AM Lorenzo Pieralisi > > > > wrote: > > > > > On Fri, Jun 23, 2023 at 10:40:54AM -0400, Jim Quinlan wrote: > > > > > > This commit adds the boolean "brcm,enable-l1ss" property: > > > > > > > > > > > > The Broadcom STB/CM PCIe HW -- a core that is also used by RPi SOCs -- > > > > > > requires the driver probe() to deliberately place the HW one of three > > > > > > CLKREQ# modes: > > > > > > > > > > > > (a) CLKREQ# driven by the RC unconditionally > > > > > > (b) CLKREQ# driven by the EP for ASPM L0s, L1 > > > > > > (c) Bidirectional CLKREQ#, as used for L1 Substates (L1SS). > > > > > > > > > > > > The HW+driver can tell the difference between downstream devices that > > > > > > need (a) and (b), but does not know when to configure (c). All devices > > > > > > should work fine when the driver chooses (a) or (b), but (c) may be > > > > > > desired to realize the extra power savings that L1SS offers. So we > > > > > > introduce the boolean "brcm,enable-l1ss" property to inform the driver > > > > > > that (c) is desired. Setting this property only makes sense when the > > > > > > downstream device is L1SS-capable and the OS is configured to activate > > > > > > this mode (e.g. policy==powersupersave). > > > > > > > > > > > > This property is already present in the Raspian version of Linux, but the > > > > > > upstream driver implementation that follows adds more details and > > > > > > discerns between (a) and (b). > > > > > > > > > > > > Signed-off-by: Jim Quinlan > > > > > > Reviewed-by: Rob Herring > > > > > > --- > > > > > > Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml | 9 +++++++++ > > > > > > 1 file changed, 9 insertions(+) > > > > > > > > > > > > diff --git a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml > > > > > > index 7e15aae7d69e..8b61c2179608 100644 > > > > > > --- a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml > > > > > > +++ b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml > > > > > > @@ -64,6 +64,15 @@ properties: > > > > > > > > > > > > aspm-no-l0s: true > > > > > > > > > > > > + brcm,enable-l1ss: > > > > > > + description: Indicates that PCIe L1SS power savings > > > > > > + are desired, the downstream device is L1SS-capable, and the > > > > > > + OS has been configured to enable this mode. For boards > > > > > > > > > > What does this mean ? I don't think DT properties are supposed > > > > > to carry information related to how the OS is configured. > > > > > > > > The DT setting in question is unrelated to the statement "and the OS > > > > has been configured to > > > > enable this mode". > > > > > > > > This is merely saying that even if you enable "brcm,l1ss-enable" > > > > that you may not get L1SS power savings w/o setting > > > > "CONFIG_PCIEASPM_POWER_SUPERSAVE=y". > > > > I mentioned that exact term but a reviewer nakked it because > > > > apparently DT descriptions should not be OS specific. > > > > > > > > I am actually open for this to be a command-line option but I wanted to honor > > > > what the Raspian OS folks have already done. RaspianOS already has > > > > "brcm,enable-l1ss" > > > > set in their DTS files. > > > > > > This is about the mainline kernel, I don't have any visibility into > > > downstream kernels (where that property management was added without DT > > > and PCI maintainers supervision). > > > > > > Raspian OS folks' choice is theirs but it can't and it shouldn't override > > > the mainline review process even though I understand the position you > > > are in. > > > > Understood, but using the command line has its warts as well; I now recall the > > discussion Bjorn and I had regarding this option. I'm pretty sure > > that upstreaam will not allow the following > > possible command line kernel params: > > > > brcm,enable-l1ss > > pci=brcm,entable-l1ss > > > > Bjorn suggested using the documented but (IMO) obscure and rarely > > used format > > > > pci=[:]:.[/.]*pci::[::] > > > > but this is just going in the wrong direction; here's why. Using the > > above iformat s completely dependent on the > > PCI "linux-domaiin" property, a non-HW related DT property I might > > add. Since "linux-domain" is already > > a valid and well-used DT property, and the value of the above > > command line format is dependent > > on the value of the "linux-domain", why not be consistent and let > > "brcm,enable-l1ss" be a Broadcom specific property? > > I am just asking to add a module_param to the host controller driver. A module_param sounds possible to me. IIRC the bidirectional CLKREQ# (config (c)) has been tested and there are no known problems even if the OS doesn't enable L1SS. The only issue (again, IIRC) is that the hardware engineer has unspecified reservations about it. Is there any room to make (c) the default and have a module_param to *disable* the L1SS support? I think the driver knows enough to then select (a) or (b) by itself. Bjorn