[PATCH v2] PCI: qcom: Ensure that PERST is asserted for at least 100 ms

Niklas Cassel
2019-05-29T09:44:05Z

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.

Fixes: 82a823833f4e ("PCI: qcom: Add Qualcomm PCIe controller driver")
Signed-off-by: Niklas Cassel <niklas.cassel@linaro.org>
Acked-by: Stanimir Varbanov <svarbanov@mm-sol.com>
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