linux-kernel - Re: [PATCH] PCI: qcom: Don't deassert reset GPIO during probe

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Message-ID: <20190213152352.GB417@e107981-ln.cambridge.arm.com>
Date:   Wed, 13 Feb 2019 15:23:52 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Stanimir Varbanov <svarbanov@...sol.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Khasim Syed Mohammed <khasim.mohammed@...aro.org>,
        Niklas Cassel <niklas.cassel@...aro.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH] PCI: qcom: Don't deassert reset GPIO during probe

On Fri, Jan 25, 2019 at 03:26:16PM -0800, Bjorn Andersson wrote:
> Acquiring the reset GPIO low means that reset is being deasserted, this
> is followed almost immediately with qcom_pcie_host_init() asserting it,
> initializing it and then finally deasserting it again, for the link to
> come up.
> 
> Some PCIe devices requires a minimum time between the initial deassert
> and subsequent reset cycles. In a platform that boots with the reset
> GPIO asserted this requirement is being violated by this deassert/assert
> pulse.
> 
> Acquiring the reset GPIO high will prevent this by matching the state to
> the subsequent asserted state.
> 
> Cc: stable@...r.kernel.org

Missing Fixes: tag, please provide me one so that I can proceed.

Lorenzo

> Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> ---
>  drivers/pci/controller/dwc/pcie-qcom.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index d185ea5fe996..a7f703556790 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -1228,7 +1228,7 @@ static int qcom_pcie_probe(struct platform_device *pdev)
>  
>  	pcie->ops = of_device_get_match_data(dev);
>  
> -	pcie->reset = devm_gpiod_get_optional(dev, "perst", GPIOD_OUT_LOW);
> +	pcie->reset = devm_gpiod_get_optional(dev, "perst", GPIOD_OUT_HIGH);
>  	if (IS_ERR(pcie->reset)) {
>  		ret = PTR_ERR(pcie->reset);
>  		goto err_pm_runtime_put;
> -- 
> 2.18.0
>