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Date: Fri, 12 Apr 2024 15:22:16 -0500
From: Bjorn Helgaas <helgaas@kernel.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
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Subject: Re: [PATCH v12 8/8] PCI: endpoint: Remove "core_init_notifier" flag
Message-ID: <20240412202216.GA14590@bhelgaas>
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In-Reply-To: <20240327-pci-dbi-rework-v12-8-082625472414@linaro.org>

On Wed, Mar 27, 2024 at 02:43:37PM +0530, Manivannan Sadhasivam wrote:
> "core_init_notifier" flag is set by the glue drivers requiring refclk from
> the host to complete the DWC core initialization. Also, those drivers will
> send a notification to the EPF drivers once the initialization is fully
> completed using the pci_epc_init_notify() API. Only then, the EPF drivers
> will start functioning.
> 
> For the rest of the drivers generating refclk locally, EPF drivers will
> start functioning post binding with them. EPF drivers rely on the
> 'core_init_notifier' flag to differentiate between the drivers.
> Unfortunately, this creates two different flows for the EPF drivers.
> 
> So to avoid that, let's get rid of the "core_init_notifier" flag and follow
> a single initialization flow for the EPF drivers. This is done by calling
> the dw_pcie_ep_init_notify() from all glue drivers after the completion of
> dw_pcie_ep_init_registers() API. This will allow all the glue drivers to
> send the notification to the EPF drivers once the initialization is fully
> completed.

Thanks for doing this!  I think this is a significantly nicer
solution than core_init_notifier was.

One question: both qcom and tegra194 call dw_pcie_ep_init_registers()
from an interrupt handler, but they register that handler in a
different order with respect to dw_pcie_ep_init().

I don't know what actually starts the process that leads to the
interrupt, but if it's dw_pcie_ep_init(), then one of these (qcom, I
think) must be racy:

  qcom_pcie_ep_probe
    dw_pcie_ep_init                                             <- A
    qcom_pcie_ep_enable_irq_resources
      devm_request_threaded_irq(qcom_pcie_ep_perst_irq_thread)  <- B

  qcom_pcie_ep_perst_irq_thread
    qcom_pcie_perst_deassert
      dw_pcie_ep_init_registers

  tegra_pcie_dw_probe
    tegra_pcie_config_ep
      devm_request_threaded_irq(tegra_pcie_ep_pex_rst_irq)      <- B
      dw_pcie_ep_init                                           <- A

  tegra_pcie_ep_pex_rst_irq
    pex_ep_event_pex_rst_deassert
      dw_pcie_ep_init_registers

Whatever the right answer is, I think qcom and tegra194 should both
order dw_pcie_ep_init() and the devm_request_threaded_irq() the same
way.

Bjorn