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 393FAEE49B0 for ; Wed, 23 Aug 2023 16:29:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237117AbjHWQ3T (ORCPT ); Wed, 23 Aug 2023 12:29:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50302 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236790AbjHWQ3S (ORCPT ); Wed, 23 Aug 2023 12:29:18 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E5128E68; Wed, 23 Aug 2023 09:29:16 -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)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 5F2E9665AF; Wed, 23 Aug 2023 16:29:16 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4D07BC433C7; Wed, 23 Aug 2023 16:29:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1692808155; bh=Zi4bGB1nlQ9h1YzG/CseWbSGhx/AV/hdXwf5BexuN+E=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=XtrHyHT+hjH8UsOMycKo8Zv6o2hy19qGD1QpBG5qfA0mAhLbvp2cMYrunhYovjQ2a viB+QzcYg0ZxmfGpdHVWCam8ygbf+cq8vTb0eIZ3wPXaH/88yMUoRsJUV92TPHuC0m KUsX3qkJgqkVV0hiWw+UTKeDcIfgK2gfKI/E8E/+13DrjUcE86GtPeOoENCKNxRMD6 Qcp+brVEfYwN3Unt+G/cTRCTSW2IBD+X2AEbG3B/5fE5z7+J32r5jqynIiNmXbXjp8 MYNRLsZmfRwYMgfvtZBDbmXHku7WSAops8Upy1yT8ceINU5GEBJPgm1K9LQJdiI5WF iBhKx1N9GztIA== Date: Wed, 23 Aug 2023 18:29:08 +0200 From: Lorenzo Pieralisi To: Rob Herring 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?= , 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: References: <20230623144100.34196-1-james.quinlan@broadcom.com> <20230623144100.34196-2-james.quinlan@broadcom.com> 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 09:48:40AM -0500, Rob Herring wrote: > On Wed, Aug 23, 2023 at 2:30 AM 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. > > Yeah, probably the OS part should be dropped. I will drop it - if you don't mind. > > > > > 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. > > Sure, but we shouldn't change things just to be different from > downstream. If we're only discussing the color of the shed, then no > point changing it. Sure, no problem. > > > 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. > > FWIW, gregkh pretty much always nacks new module parameters. Fine by me. > > Anyway - time is running out for v6.6, I need Rob's feedback, if I don't > > hear from him today I will merge the last three patches and postpone the > > discussion. > > You've already got my reviewed-by. If you aren't happy with this, then > fine. I don't know enough about L1SS to comment further. Is it > normally always supported or discoverable? If so, then I'd think we'd > want it default enabled with a disable override flag. Maybe it should > be generic? It is not that I am not happy with it - we asked questions to understand what this property was for, I think that's normal. I will merge this series as-is. Lorenzo