linux-kernel - [PATCH 4.19 231/271] PCI: qcom: Ensure that PERST is asserted for at least 100 ms

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Message-Id: <20190724191714.957798561@linuxfoundation.org>
Date:   Wed, 24 Jul 2019 21:21:40 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Niklas Cassel <niklas.cassel@...aro.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Stanimir Varbanov <svarbanov@...sol.com>
Subject: [PATCH 4.19 231/271] PCI: qcom: Ensure that PERST is asserted for at least 100 ms

From: Niklas Cassel <niklas.cassel@...aro.org>

commit 64adde31c8e996a6db6f7a1a4131180e363aa9f2 upstream.

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 r2.0, section
2.2, "PERST# Signal" 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.

Fixes: 82a823833f4e ("PCI: qcom: Add Qualcomm PCIe controller driver")
Signed-off-by: Niklas Cassel <niklas.cassel@...aro.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Acked-by: Stanimir Varbanov <svarbanov@...sol.com>
Cc: stable@...r.kernel.org # 4.5+
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/pci/controller/dwc/pcie-qcom.c |    2 ++
 1 file changed, 2 insertions(+)

--- 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
 
 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);
 }