linux-kernel - Re: [PATCH 01/11] PCI: qcom-ep: Disable resources unconditionally during PERST# assert

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Date: Fri, 22 Mar 2024 17:08:22 +0100
From: Niklas Cassel <cassel@...nel.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Jonathan Hunter <jonathanh@...dia.com>,
	Jingoo Han <jingoohan1@...il.com>,
	Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
	linux-pci@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	linux-kernel@...r.kernel.org, mhi@...ts.linux.dev,
	linux-tegra@...r.kernel.org
Subject: Re: [PATCH 01/11] PCI: qcom-ep: Disable resources unconditionally
 during PERST# assert

On Thu, Mar 14, 2024 at 08:53:40PM +0530, Manivannan Sadhasivam wrote:
> All EP specific resources are enabled during PERST# deassert. As a counter
> operation, all resources should be disabled during PERST# assert. There is
> no point in skipping that if the link was not enabled.
> 
> This will also result in enablement of the resources twice if PERST# got
> deasserted again. So remove the check from qcom_pcie_perst_assert() and
> disable all the resources unconditionally.
> 
> Fixes: f55fee56a631 ("PCI: qcom-ep: Add Qualcomm PCIe Endpoint controller driver")
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> ---
>  drivers/pci/controller/dwc/pcie-qcom-ep.c | 6 ------
>  1 file changed, 6 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-qcom-ep.c b/drivers/pci/controller/dwc/pcie-qcom-ep.c
> index 2fb8c15e7a91..50b1635e3cbb 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom-ep.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom-ep.c
> @@ -500,12 +500,6 @@ static int qcom_pcie_perst_deassert(struct dw_pcie *pci)
>  static void qcom_pcie_perst_assert(struct dw_pcie *pci)
>  {
>  	struct qcom_pcie_ep *pcie_ep = to_pcie_ep(pci);
> -	struct device *dev = pci->dev;
> -
> -	if (pcie_ep->link_status == QCOM_PCIE_EP_LINK_DISABLED) {
> -		dev_dbg(dev, "Link is already disabled\n");
> -		return;
> -	}
>  
>  	dw_pcie_ep_cleanup(&pci->ep);
>  	qcom_pcie_disable_resources(pcie_ep);

Are you really sure that this is safe?

I think I remember seeing some splat in dmesg if some clks, or maybe it
was regulators, got disabled while already being disabled.

Perhaps you could test it by simply calling:
qcom_pcie_disable_resources();
twice here, and see if you see and splat in dmesg.


Kind regards,
Niklas