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

Manivannan Sadhasivam
2024-03-26T07:44:37Z

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@linaro.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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