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[104.188.17.28]) by smtp.gmail.com with ESMTPSA id a64sm6011216pgc.53.2019.05.25.22.48.49 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sat, 25 May 2019 22:48:49 -0700 (PDT) Date: Sat, 25 May 2019 22:49:18 -0700 From: Bjorn Andersson To: Niklas Cassel Cc: Stanimir Varbanov , Andy Gross , David Brown , Lorenzo Pieralisi , Bjorn Helgaas , linux-pci@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] PCI: qcom: Ensure that PERST is asserted for at least 100 ms Message-ID: <20190526054918.GK2085@tuxbook-pro> References: <20190523194409.17718-1-niklas.cassel@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190523194409.17718-1-niklas.cassel@linaro.org> User-Agent: Mutt/1.11.4 (2019-03-13) Sender: linux-arm-msm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org On Thu 23 May 12:44 PDT 2019, 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. > > 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." > > Add a sleep of 100 ms before deasserting PERST, in order to ensure that > we are compliant with the spec. > > Signed-off-by: Niklas Cassel Reviewed-by: Bjorn Andersson > --- > 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..cae24376237c 100644 > --- a/drivers/pci/controller/dwc/pcie-qcom.c > +++ b/drivers/pci/controller/dwc/pcie-qcom.c > @@ -1110,6 +1110,8 @@ static int qcom_pcie_host_init(struct pcie_port *pp) > if (IS_ENABLED(CONFIG_PCI_MSI)) > dw_pcie_msi_init(pp); > > + /* Ensure that PERST has been asserted for at least 100 ms */ > + msleep(100); > qcom_ep_reset_deassert(pcie); > > ret = qcom_pcie_establish_link(pcie); > -- > 2.21.0 >