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

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Message-ID: <20190530155453.GF13993@redmoon>
Date:   Thu, 30 May 2019 16:54:53 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Niklas Cassel <niklas.cassel@...aro.org>
Cc:     Stanimir Varbanov <svarbanov@...sol.com>,
        Andy Gross <agross@...nel.org>,
        David Brown <david.brown@...aro.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>, stable@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] PCI: qcom: Ensure that PERST is asserted for at least
 100 ms

On Wed, May 29, 2019 at 11:43:52AM +0200, 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.
> 
> Fixes: 82a823833f4e ("PCI: qcom: Add Qualcomm PCIe controller driver")
> Signed-off-by: Niklas Cassel <niklas.cassel@...aro.org>
> Acked-by: Stanimir Varbanov <svarbanov@...sol.com>
> Cc: stable@...r.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(+)

Applied to pci/qcom for v5.3, thanks.

Lorenzo

> 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
>