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From:   Niklas Cassel <niklas.cassel@linaro.org>
To:     Stanimir Varbanov <svarbanov@mm-sol.com>,
        Andy Gross <agross@kernel.org>,
        David Brown <david.brown@linaro.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Bjorn Helgaas <bhelgaas@google.com>
Cc:     Niklas Cassel <niklas.cassel@linaro.org>,
        linux-pci@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH] PCI: qcom: Ensure that PERST is asserted for at least 100 ms
Date:   Thu, 23 May 2019 21:44:08 +0200
Message-Id: <20190523194409.17718-1-niklas.cassel@linaro.org>
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Sender: linux-kernel-owner@vger.kernel.org
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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 <niklas.cassel@linaro.org>
---
 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