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

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Date: Tue, 26 Mar 2024 13:14:29 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Niklas Cassel <cassel@...nel.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 Fri, Mar 22, 2024 at 05:08:22PM +0100, Niklas Cassel wrote:
> 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.
> 

Calling the disable_resources() function twice will definitely result in the
splat. But here PERST# is level triggered, so I don't see how the EP can see
assert twice.

Am I missing something?

- Mani

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