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 799D4C369D1 for ; Fri, 25 Apr 2025 12:11:14 +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:References: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:List-Owner; bh=dVvqcqHhsiFsg0bFCeVfP4i0OhnLHgFo/lnbyU/FJbQ=; b=41kxM0qnlGEQM3twlkWbYFVIvA cYFeBIB8diV3nJS+8uw42ZZzKuP9KmnGro4C5vtp5IrMVtHI9SLbqODpShJHssO7qqC3REkfTTsXU PkjR1xX7LUcH2mEup0b9ie3OP472sRny0Xz1PlMDgWk0HdD1eXev9FkNcSqipHzKvc82tCygdL4Sd rOxnNgOy26zvSRtd5+e5zt4E0yaLk1TXacWUnmF71nCMZ2JAYDfLusHvi2r0mN+dN+3bqq04hC+qR C79El55YD/e1LyvPPXmWV90pumRISn4f0hwDJ+5oH4wE7bGDgVW1YfpsY+S0QIQgi98hmxFNyuePB XKpmemPw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1u8HtY-0000000H4ar-1iG5; Fri, 25 Apr 2025 12:11:04 +0000 Received: from sea.source.kernel.org ([172.234.252.31]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1u8GDG-0000000GilD-2z4G; Fri, 25 Apr 2025 10:23:19 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id A97044A936; Fri, 25 Apr 2025 10:23:16 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8E63DC4CEE4; Fri, 25 Apr 2025 10:23:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1745576598; bh=gADYdVRlTedtCvztmIJXcTmZi2Paf3CILRLCGSYZMlg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=rH84NfFdudOaN325xEfK5AzM51x1HjdnMFP4ugILf+mRs51A40wGY1q0K5ZiBJNjq HYX5nWAbLLY7t0ctfyuMRalpk81pv5iAWNe0bQfuEsgeC+7t2oQQxvv24ehUFtmGZS kxPrVZ1OFGciFAGfv4dqQeo6285b1Y6R/IZf7ed9MkUD9oFOBealWK4B5iIMIlMP7h bRITLkwoCfrBj9ENyMXtrsXQPxFY3YZQdrkgQRxUAQHBsLNvZ9tbsw2c16h7pR/3gS dVSm8Uifhaa4x2FBCxxE+V9ND5wTMudCTn7HnPdj+D9MRXyGWJR7diOUonJds9bJR3 oOkSnVeLy46eg== Date: Fri, 25 Apr 2025 12:23:12 +0200 From: Niklas Cassel To: Hans Zhang <18255117159@163.com> Cc: lpieralisi@kernel.org, kw@linux.com, bhelgaas@google.com, heiko@sntech.de, thomas.petazzoni@bootlin.com, manivannan.sadhasivam@linaro.org, yue.wang@amlogic.com, pali@kernel.org, neil.armstrong@linaro.org, robh@kernel.org, jingoohan1@gmail.com, khilman@baylibre.com, jbrunet@baylibre.com, martin.blumenstingl@googlemail.com, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-amlogic@lists.infradead.org, linux-rockchip@lists.infradead.org Subject: Re: [PATCH v2 1/2] PCI: Configure root port MPS to hardware maximum during host probing Message-ID: References: <20250425095708.32662-1-18255117159@163.com> <20250425095708.32662-2-18255117159@163.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250425095708.32662-2-18255117159@163.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250425_032318_795334_62483E73 X-CRM114-Status: GOOD ( 20.00 ) 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 Fri, Apr 25, 2025 at 05:57:07PM +0800, Hans Zhang wrote: > Current PCIe initialization logic may leave root ports operating with > non-optimal Maximum Payload Size (MPS) settings. While downstream device > configuration is handled during bus enumeration, root port MPS values > inherited from firmware or hardware defaults might not utilize the full > capabilities supported by the controller hardware. This can result in > suboptimal data transfer efficiency across the PCIe hierarchy. > > During host controller probing phase, when PCIe bus tuning is enabled, > the implementation now configures root port MPS settings to their > hardware-supported maximum values. By iterating through bridge devices > under the root bus and identifying PCIe root ports, each port's MPS is set > to 128 << pcie_mpss to match the device's maximum supported payload size. > The Max Read Request Size (MRRS) is subsequently adjusted through existing > companion logic to maintain compatibility with PCIe specifications. > > Explicit initialization at host probing stage ensures consistent PCIe > topology configuration before downstream devices perform their own MPS > negotiations. This proactive approach addresses platform-specific > requirements where controller drivers depend on properly initialized root > port settings, while maintaining backward compatibility through > PCIE_BUS_TUNE_OFF conditional checks. Hardware capabilities are fully > utilized without altering existing device negotiation behaviors. > > Signed-off-by: Hans Zhang <18255117159@163.com> Perhaps Mani deserves a Suggested-by tag? > --- > drivers/pci/probe.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c > index 364fa2a514f8..3973c593fdcf 100644 > --- a/drivers/pci/probe.c > +++ b/drivers/pci/probe.c > @@ -3206,6 +3206,7 @@ EXPORT_SYMBOL_GPL(pci_create_root_bus); > int pci_host_probe(struct pci_host_bridge *bridge) > { > struct pci_bus *bus, *child; > + struct pci_dev *dev; > int ret; > > pci_lock_rescan_remove(); > @@ -3228,6 +3229,17 @@ int pci_host_probe(struct pci_host_bridge *bridge) > */ > pci_assign_unassigned_root_bus_resources(bus); > > + if (pcie_bus_config != PCIE_BUS_TUNE_OFF) { > + /* Configure root ports MPS to be MPSS by default */ > + for_each_pci_bridge(dev, bus) { > + if (pci_pcie_type(dev) != PCI_EXP_TYPE_ROOT_PORT) > + continue; > + > + pcie_write_mps(dev, 128 << dev->pcie_mpss); > + pcie_write_mrrs(dev); The comment says configure MPS, but the code also calls pcie_write_mrrs(). Should we update the comment or should we remove the call to pcie_write_mrrs()? Note that even when calling pcie_write_mrrs(), it will not update MRRS for the common case (pcie_bus_config == PCIE_BUS_DEFAULT). Kind regards, Niklas