From: Bjorn Andersson <bjorn.andersson@linaro.org>
To: Niklas Cassel <niklas.cassel@linaro.org>
Cc: 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>,
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
Date: Sat, 25 May 2019 22:49:18 -0700 [thread overview]
Message-ID: <20190526054918.GK2085@tuxbook-pro> (raw)
In-Reply-To: <20190523194409.17718-1-niklas.cassel@linaro.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 <niklas.cassel@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@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
>
prev parent reply other threads:[~2019-05-26 5:48 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-23 19:44 [PATCH] PCI: qcom: Ensure that PERST is asserted for at least 100 ms Niklas Cassel
2019-05-24 12:43 ` Marc Gonzalez
2019-05-27 17:15 ` Niklas Cassel
2019-05-28 20:36 ` Stanimir Varbanov
2019-05-26 5:49 ` Bjorn Andersson [this message]
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