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 2E4EBCAC59F for ; Wed, 17 Sep 2025 22:24:11 +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=3Oy+tmQ4yRxvWrPaS60lkLVNG+mJ8pW0sRMc+mIO5dU=; b=VPr5QiR3JbRlDP Qoobyyx+jMDVDjTjR33tx7tjOHqLJibnHEEvfk0lA0b1XvVBU+cnDn2n0C3kAWc54Z0GVT03gfper 6W6aaR4pnP0Xd3eJ5yHYFXFverRNnOrzKhE44lvBjorw3CDd8xBZKX19XCQgt8m/L8zLrHeCq/Z4Y nW40odNaw2sCGPHJeZB1GgKPTYFfkx9oRqP41jmSG5YB9Xo+bJLc/2B7f8+es4FSG3vysawtxfOfb 31z9TQ8fitMa4kSV/LQjLe32aXVdLrOy8gXrbQs8xSmQoMEp0reYP3XnXgrqUIzYvDbC9G8tD5YQe LtwEyZtewLXg1Jn5jtGw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uz0ZG-0000000FEmt-0GW6; Wed, 17 Sep 2025 22:24:02 +0000 Received: from sea.source.kernel.org ([2600:3c0a:e001:78e:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1uz0ZD-0000000FEmT-1lCZ for linux-arm-kernel@lists.infradead.org; Wed, 17 Sep 2025 22:24:00 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 1B53A405CD; Wed, 17 Sep 2025 22:23:58 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id BD618C4CEE7; Wed, 17 Sep 2025 22:23:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1758147838; bh=UnGcqVgS4GD/7L0fDg931OMlNpuv6k722YO8GEx8cqA=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=FscnWqJ9AamopYzEys8/f8cfqCwSnkZMxdUlYjDRJrUENMYwk9TZD/ySS+hqZK6qb zXtzx0R0Vbs176BSgMdIm3es4SHf8lKbT9d95iBS23JJFixlpAM9nYTx0DNrS+vNla rpraXAObjE0eOTtLZmTfa24eaOqBaSgU3rBTCY3ogNWpoDEOO3XTqs0LtQRZALXwcE bG7v0Wfz/2XkFbuKVqtuO2sWW6rJjGVTdO/wrwOumeDzouAjjEkddtQaAwZ4GWG/qQ XyHMEjTT13N7fXH3xfeLMoGWxDo7cKsR+VEjeNa+hOePBnXg/+3kf/PoReZD3LCB0u 5DXf6T+YnmBnw== Date: Wed, 17 Sep 2025 17:23:56 -0500 From: Bjorn Helgaas To: Richard Zhu Cc: frank.li@nxp.com, jingoohan1@gmail.com, l.stach@pengutronix.de, lpieralisi@kernel.org, kwilczynski@kernel.org, mani@kernel.org, robh@kernel.org, bhelgaas@google.com, shawnguo@kernel.org, s.hauer@pengutronix.de, kernel@pengutronix.de, festevam@gmail.com, linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org, imx@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 2/2] PCI: imx6: Add a method to handle CLKREQ# override active low Message-ID: <20250917222356.GA1879221@bhelgaas> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250917093751.1520050-3-hongxing.zhu@nxp.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250917_152359_483030_03495C2A X-CRM114-Status: GOOD ( 13.46 ) 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 Wed, Sep 17, 2025 at 05:37:51PM +0800, Richard Zhu wrote: > The CLKREQ# is an open drain, active low signal that is driven low by > the card to request reference clock. > > But the CLKREQ# maybe reserved on some old device, compliant with CEM > r3.0 or before. Thus, this signal wouldn't be driven low by these old > devices. Can you include a citation to a relevant section in the CEM spec? Maybe the point is that CLKREQ# is an optional signal added in PCIe CEM r4.0, sec 2? If that's accurate, we can add it when applying, no need to repost for that. > Since the reference clock controlled by CLKREQ# may be required by i.MX > PCIe host too. To make sure this clock is ready even when the CLKREQ# > isn't driven low by the card(e.x old cards described above), force > CLKREQ# override active low for i.MX PCIe host during initialization. > > The CLKREQ# override can be cleared safely when supports-clkreq is > present and PCIe link is up later. Because the CLKREQ# would be driven > low by the card in this case.