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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id B469AC369B2 for ; Thu, 17 Apr 2025 16:54:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:References: List-Owner; bh=8Xvf44CIcjF/gcpwz3DXiuSv/K80GzZacd9PQxqWtiQ=; b=TW6bPl8YB3z0Gq poCL84h+iDnaDPgwX8kSlWuZJ3XNeNNRU9qroIvHHSeyzWtUv5m/pJgIsTBlwMi7jrfncfz26tyKF Y76RfFWDWeZys3AoMFOYwpAFVKqnSrv5bJkTnRwoD6qfPzcm84v2iO94kGT3HvWDSMwqD3xqagVy8 4jleDR/96vckh9dRsdOhrVpnq/ZHPAox3XaFpZbcM3SRfRfnnKQE4cEujGp/FIiN05gqSljV+sbac tUqg7JUp1AqYnI5dd4S3Trm9K+togzkfgOLmKN9QPlwY+3Vd6zT6D1ogsdafqPtNL3uoRVeTC4ORs 3e3G92sJcIxtZ45cD8Ng==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1u5SVG-0000000Djqn-2dmU; Thu, 17 Apr 2025 16:54:18 +0000 Received: from dfw.source.kernel.org ([139.178.84.217]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1u5STN-0000000DjQP-3E4l; Thu, 17 Apr 2025 16:52:23 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id 085CC5C547C; Thu, 17 Apr 2025 16:50:04 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8E678C4CEE4; Thu, 17 Apr 2025 16:52:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1744908740; bh=Us5KGJ06EpniB9Lq8EokWDK/QvSzQfAUWxcm5rSlsLM=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=gTtyo+yR7ipvHNpFgGtC0rJ0C7obiBFQy/2hOweKNa78SHw1xMChSfPjq0ku5R4Dl nZEmNhITeZNFbB3imQka3GltevciNGZiW8rZ3V4JEEc/0nHvCs8LuNkERn1W2hDgr4 ssR6qKGmmp2I6O8rN6RX6Rvfwc/mbeG/nUZkveU6BgZrJS9UqZ3xOp+c13Lu8NUQGF JCqnk7FL8fUP6vdlxy3NfIPIphVafLJuL915uDh1At6Y8muC1rdff7+XPkhOnDs2JT 0cxb5bW7V45t7oz0hjkE77COfGnkywwEaVQqFIEHJ5yxGD24ThUFE1yhd5M7AkIviY cCaIg9TeuBhrA== Date: Thu, 17 Apr 2025 11:52:19 -0500 From: Bjorn Helgaas To: Niklas Cassel Cc: Hans Zhang <18255117159@163.com>, Shawn Lin , lpieralisi@kernel.org, kw@linux.com, bhelgaas@google.com, heiko@sntech.de, manivannan.sadhasivam@linaro.org, robh@kernel.org, jingoohan1@gmail.com, thomas.richard@bootlin.com, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-rockchip@lists.infradead.org Subject: Re: [PATCH] PCI: dw-rockchip: Configure max payload size on host init Message-ID: <20250417165219.GA115235@bhelgaas> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250417_095221_891012_11A8BE63 X-CRM114-Status: GOOD ( 26.67 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Apr 17, 2025 at 10:39:49AM +0200, Niklas Cassel wrote: > On Thu, Apr 17, 2025 at 04:07:51PM +0800, Hans Zhang wrote: > > On 2025/4/17 15:48, Niklas Cassel wrote: > > > > Hi Niklas and Shawn, > > > > Thank you very much for your discussion and reply. > > > > I tested it on RK3588 and our platform. By setting pci=pcie_bus_safe, the > > maximum MPS will be automatically matched in the end. > > > > So is my patch no longer needed? For RK3588, does the customer have to > > configure CONFIG_PCIE_BUS_SAFE or pci=pcie_bus_safe? > > > > Also, for pci-meson.c, can the meson_set_max_payload be deleted? > > I think the only reason why this works is because > pcie_bus_configure_settings(), in the case of > pcie_bus_config == PCIE_BUS_SAFE, will walk the bus and set MPS in > the bridge to the lowest of the downstream devices: > https://github.com/torvalds/linux/blob/v6.15-rc2/drivers/pci/probe.c#L2994-L2999 > > So Hans, if you look at lspci for the other RCs/bridges that don't > have any downstream devices connected, do they also show DevCtl.MPS 256B > or do they still show 128B ? > > One could argue that for all policies (execept for maybe PCIE_BUS_TUNE_OFF), > pcie_bus_configure_settings() should start off by initializing DevCtl.MPS to > DevCap.MPS (for the bridge itself), and after that pcie_bus_configure_settings() > can override it depending on policy, e.g. set MPS to 128B in case of > pcie_bus_config == PCIE_BUS_PEER2PEER, or walk the bus in case of > pcie_bus_config == PCIE_BUS_SAFE. > > That way, we should be able to remove the setting for pci-meson.c as well. Thanks, I came here to say basically the same thing. Ideally I think the generic code in pcie_bus_configure_settings() should be able to increase MPS or decrease it such that neither meson_set_max_payload() nor rockchip_pcie_set_max_payload() is required. However, the requirement to pick a Kconfig setting makes it a mess. I would love to get rid of those Kconfig symbols. I don't like the command-line parameters either, but it would definitely be an improvement if we could nuke the Kconfig symbols and rely on the command-line parameters. It's also a problem when devices are hot-added after the hierarchy has already been set up because the new device might not work correctly in the existing config. It's a hard problem to solve. For new platforms without an install base, maybe it would be easier to rely on the command-line parameters since there aren't a bunch of users that would have to change the Kconfig. Bjorn