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 X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_MUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D1A43C28CC3 for ; Thu, 30 May 2019 15:49:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B597F25D1C for ; Thu, 30 May 2019 15:49:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727216AbfE3Ptb (ORCPT ); Thu, 30 May 2019 11:49:31 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:38924 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725961AbfE3Ptb (ORCPT ); Thu, 30 May 2019 11:49:31 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D74CC341; Thu, 30 May 2019 08:49:30 -0700 (PDT) Received: from redmoon (e121166-lin.cambridge.arm.com [10.1.196.255]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 393A33F59C; Thu, 30 May 2019 08:49:29 -0700 (PDT) Date: Thu, 30 May 2019 16:49:26 +0100 From: Lorenzo Pieralisi To: Bjorn Helgaas Cc: Niklas Cassel , Stanimir Varbanov , Andy Gross , David Brown , stable@vger.kernel.org, linux-pci@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] PCI: qcom: Ensure that PERST is asserted for at least 100 ms Message-ID: <20190530154926.GE13993@redmoon> References: <20190529094352.5961-1-niklas.cassel@linaro.org> <20190529125232.GA28250@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190529125232.GA28250@google.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Wed, May 29, 2019 at 07:52:32AM -0500, Bjorn Helgaas wrote: > On Wed, May 29, 2019 at 11:43:52AM +0200, Niklas Cassel wrote: > > Currently, there is only a 1 ms sleep after asserting PERST. > > > > Reading the datasheets for different endpoints, some require PERST to be > > asserted for 10 ms in order for the endpoint to perform a reset, others > > require it to be asserted for 50 ms. > > > > Several SoCs using this driver uses PCIe Mini Card, where we don't know > > what endpoint will be plugged in. > > I think this patch is absolutely the right thing to do. We don't know > what might be plugged in, so we should support arbitrary endpoints. > > One could imagine some sort of DT property to identify closed > environments where there is no need to support arbitrary endpoints and > it might be desirable to reduce the delay. But that should wait > until there's a need for it and if the need *does* arise, hopefully > the definition of such a property could be generic across all SoCs. > > > The PCI Express Card Electromechanical Specification specifies: > > "On power up, the deassertion of PERST# is delayed 100 ms (TPVPERL) from > > the power rails achieving specified operating limits." > > It'd be nice to include the complete citation, i.e., "PCI Express Card > Electromechanical Specification r2.0, sec 2.2" I will add it and merge the patch. Thanks, Lorenzo > > Add a sleep of 100 ms before deasserting PERST, in order to ensure that > > we are compliant with the spec. > > > > Fixes: 82a823833f4e ("PCI: qcom: Add Qualcomm PCIe controller driver") > > Signed-off-by: Niklas Cassel > > Acked-by: Stanimir Varbanov > > Cc: stable@vger.kernel.org # 4.5+ > > --- > > Changes since v1: > > Move the sleep into qcom_ep_reset_deassert() > > > > drivers/pci/controller/dwc/pcie-qcom.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c > > index 0ed235d560e3..5d1713069d14 100644 > > --- a/drivers/pci/controller/dwc/pcie-qcom.c > > +++ b/drivers/pci/controller/dwc/pcie-qcom.c > > @@ -178,6 +178,8 @@ static void qcom_ep_reset_assert(struct qcom_pcie *pcie) > > > > static void qcom_ep_reset_deassert(struct qcom_pcie *pcie) > > { > > + /* Ensure that PERST has been asserted for at least 100 ms */ > > + msleep(100); > > gpiod_set_value_cansleep(pcie->reset, 0); > > usleep_range(PERST_DELAY_US, PERST_DELAY_US + 500); > > } > > -- > > 2.21.0 > >