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=-8.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,T_DKIMWL_WL_HIGH,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 9350BC28CC2 for ; Wed, 29 May 2019 12:52:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6CD412081C for ; Wed, 29 May 2019 12:52:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1559134355; bh=dGdCcGynEuU84CpifoTXESNk2YEk11Q/jGdnwOs+Z6w=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=mbdSzj79qUtWl2tmrA3gGlMuojr4XKMlSj1aXjJ9R8ATkAgh+OdqfmobnswWPYeVf u2sYcfW/NDX0vNppdEfN7bVkdJXxnhWvAcvQvgyEsP3iMaWKqD6133HIlCjRPel2m4 sCFyJHobhedzSSD/hf50+fqnqByk2FTmm2O7+ezo= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726225AbfE2Mwe (ORCPT ); Wed, 29 May 2019 08:52:34 -0400 Received: from mail.kernel.org ([198.145.29.99]:53450 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725936AbfE2Mwe (ORCPT ); Wed, 29 May 2019 08:52:34 -0400 Received: from localhost (173-25-83-245.client.mchsi.com [173.25.83.245]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id E027320673; Wed, 29 May 2019 12:52:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1559134354; bh=dGdCcGynEuU84CpifoTXESNk2YEk11Q/jGdnwOs+Z6w=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=u4ogjzOkqZR5Nbh3+cYMWEKxFsnKlIh67NoDnsZy7gFqj1L/7JUMH6XqIwXwDn6xz KMuQSOnWj9hHsqvf6Je8Jyx30JyREdjGCk42fa/ZDKy5vtlpolOQ3wsKvHXefAjzyB hNrXgkjUHo3CUGXe/TArH2W1n6B5xtyjl3oa4q64= Date: Wed, 29 May 2019 07:52:32 -0500 From: Bjorn Helgaas To: Niklas Cassel Cc: Stanimir Varbanov , Andy Gross , David Brown , Lorenzo Pieralisi , 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: <20190529125232.GA28250@google.com> References: <20190529094352.5961-1-niklas.cassel@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190529094352.5961-1-niklas.cassel@linaro.org> User-Agent: Mutt/1.10.1 (2018-07-13) 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 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" > 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 >