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 8D912EB64DA for ; Wed, 19 Jul 2023 08:05:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Message-ID: Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:References: List-Owner; bh=llXvV4S5wNSKpxMKUouAyZK/ZkeozVOQZqE9yODYxeY=; b=3OBUxY18D6lRGM 0H2nrwvslQndaFlQHtJ7tz+nBxoh5KC3eJpYoLdc1hw38JawP2kxlBnuNdeR4IAS632Kb/hkm3Zk7 bAMf1MS/nrgbhxiHH1grLG8LC8mWvTJT34ri0u8AyIpSSkOl8a8FyEJ/5r5IPdv10N4K3zQgxpL9v x8AvGsb4jb9SK7q+gYa3Mk8I/xeYjwZiRzLdBR9xXcIRRyFXFwM3vWneDFzSA99Ipcte4EKCCtuVa /kBnincRzownrwdTnXJzhs83yWlIpdVfZh9XE/hEwZzWyOP07qt6ghNsyCNEC/RHgXL3UGG3ieHgB 3Ut6uWG+nycEY87/kIXQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qM2BP-006D7A-26; Wed, 19 Jul 2023 08:05:15 +0000 Received: from desiato.infradead.org ([2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1qM2BK-006D4g-07 for linux-arm-kernel@bombadil.infradead.org; Wed, 19 Jul 2023 08:05:10 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:References; bh=iXyDZNfizCr8hOGPhlLJQ50KavRBQ5AQKPacSRrk3EE=; b=q3tAq1PP5mC6pUQNCftnPpMcCx yk9aqFYnn8oWXNv2LY/tzVJj1jcnhcBxT65LehM0SOb5slM91a7uIQjgxUixDTbErCnLgt5UnZtGu Y1QU6qKHCbNlYBvy+k1xySla3nr24qpf+l+jeF5hBVvhUyzjTpgta0GxjgnlYEJoA/Z6D3h9C8vWu B9wMCG5Z1qSQC23qm1UYAMWHHrozwzgZ5mFMPb5c99wiyO3tcKNml+c+Jz3v3JDEcoBm2qGYBKAmR WPYWFo8qF0ymij9QXMv2jHZZoxO7jiJUT7/BgL1b83UttB47tpb0jEA3PG4Q5rTcsAga0anUf97pc /RUY5Z7Q==; Received: from dfw.source.kernel.org ([139.178.84.217]) by desiato.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1qLn2u-00BiZv-12 for linux-arm-kernel@lists.infradead.org; Tue, 18 Jul 2023 15:55:33 +0000 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 B79A76167B; Tue, 18 Jul 2023 15:55:18 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8A56FC433B9; Tue, 18 Jul 2023 15:55:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1689695717; bh=XkxaNzMQrlndpmaZ6Ahex4//qnr2RKplzVyK9NA4FAs=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=bX5cTij+x74/dC4QWY3+zwYhnrlKfd4bd+c6mzDOa1cLDbU2o7xP5r85fBjHD2z9I l8TmTQP14ByqW0OOZzgqxP0yQ4VCdLyacPMuTzUQYHnWsP3oJujRfnJHnbtNyOcLFy b8gCnLR3hqFkOXSNmDgQWr9gqJxdrnyzkh0GoR9B6zBxq/d8yGXnMwmliYrvOmzgJ3 6Igf/XmWqlfRWEfIFOgaVN6lkZFLONHsUmCqxq0l15oTbyqqbXsLg2q3OjAu8lctd9 aI3mVU9RGSMJisZFb2m48ABZzssm9K5kx0nd6TanKixpFU/aqPWbrM8P83HLAWlr+p +jQiEa1Ec8lsA== Date: Tue, 18 Jul 2023 10:55:15 -0500 From: Bjorn Helgaas To: Achal Verma Cc: Vignesh Raghavendra , Lorenzo Pieralisi , Krzysztof Wilczy_ski , Rob Herring , Bjorn Helgaas , linux-omap@vger.kernel.org, linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] PCI: j721e: Delay 100ms T_PVPERL from power stable to PERST# inactive Message-ID: <20230718155515.GA483233@bhelgaas> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20230707095119.447952-1-a-verma1@ti.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230718_165531_290661_FC62490F X-CRM114-Status: GOOD ( 28.94 ) 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: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Jul 07, 2023 at 03:21:19PM +0530, Achal Verma wrote: > As per the PCIe Card Electromechanical specification REV. 5.0, PERST# > signal should be de-asserted after minimum 100ms from the time power-rails > become stable. So, to ensure 100ms delay to give sufficient time for > power-rails and refclk to become stable, change delay from 100us to 100ms. > > From PCIe Card Electromechanical specification REV. 5.0 section 2.9.2: > TPVPERL: Power stable to PERST# inactive - 100ms > > Fixes: f3e25911a430 ("PCI: j721e: Add TI J721E PCIe driver") > Signed-off-by: Achal Verma > --- > > Changes from v2: > * Fix commit message. > > Change from v1: > * Add macro for delay value. > > drivers/pci/controller/cadence/pci-j721e.c | 11 +++++------ > drivers/pci/pci.h | 2 ++ > 2 files changed, 7 insertions(+), 6 deletions(-) > > diff --git a/drivers/pci/controller/cadence/pci-j721e.c b/drivers/pci/controller/cadence/pci-j721e.c > index e70213c9060a..32b6a7dc3cff 100644 > --- a/drivers/pci/controller/cadence/pci-j721e.c > +++ b/drivers/pci/controller/cadence/pci-j721e.c > @@ -498,14 +498,13 @@ static int j721e_pcie_probe(struct platform_device *pdev) > > /* > * "Power Sequencing and Reset Signal Timings" table in > - * PCI EXPRESS CARD ELECTROMECHANICAL SPECIFICATION, REV. 3.0 > - * indicates PERST# should be deasserted after minimum of 100us > - * once REFCLK is stable. The REFCLK to the connector in RC > - * mode is selected while enabling the PHY. So deassert PERST# > - * after 100 us. > + * PCI EXPRESS CARD ELECTROMECHANICAL SPECIFICATION, REV. 5.0 > + * indicates PERST# should be deasserted after minimum of 100ms > + * after power rails achieve specified operating limits and > + * within this period reference clock should also become stable. I think the problem is not that the current code is *wrong*, because we do need to observe T_PERST-CLK, but that it failed to *also* account for T_PVPERL. There are two delays before deasserting PERST#: T_PVPERL: delay after power becomes stable T_PERST-CLK: delay after REFCLK becomes stable I assume power is enabled by phy_power_on(), and REFCLK is enabled by clk_prepare_enable(): cdns_pcie_init_phy cdns_pcie_enable_phy phy_power_on <-- power becomes stable clk_prepare_enable <-- REFCLK becomes stable if (gpiod) usleep_range gpiod_set_value_cansleep(gpiod, 1) <-- deassert PERST# I don't actually know if phy_power_on() guarantees that power is stable before it returns. But I guess that's our assumption? Similarly for clk_prepare_enable(). In any case, we have to observe both delays. They overlap, and T_PVPERL is 1000 times longer than T_PERST-CLK, so there might be enough slop in an msleep(100) to cover both, but I think I would do the simple-minded: msleep(PCIE_TPVPERL_MS); usleep_range(PCIE_TPERST_CLK_US, 2 * PCIE_TPERST_CLK_US); This is slightly more conservative than necessary because they overlap, but at least it shows that we thought about both of them. > if (gpiod) { > - usleep_range(100, 200); > + msleep(PCIE_TPVPERL_DELAY_MS); > gpiod_set_value_cansleep(gpiod, 1); I wish this local variable were named something like "perst_gpiod" instead of "gpiod". We already know from its use in gpiod_set_value_cansleep() that it's a GPIO. What's NOT obvious from the context is that this is the PERST# signal. Tangent: it looks like the DT "reset" property that I'm assuming controls PERST# is optional. How do we enforce these delays if that property is missing? > diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h > index a4c397434057..6ab2367e5867 100644 > --- a/drivers/pci/pci.h > +++ b/drivers/pci/pci.h > @@ -13,6 +13,8 @@ > > #define PCIE_LINK_RETRAIN_TIMEOUT_MS 1000 > > +#define PCIE_TPVPERL_DELAY_MS 100 /* see PCIe CEM r5.0, sec 2.9.2 */ > + > extern const unsigned char pcie_link_speed[]; > extern bool pci_early_dump; > > -- > 2.25.1 > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel