linux-kernel - Re: [PATCH 1/2] PCI: qcom-ep: Move controller cleanups to qcom_pcie_perst

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Message-ID: <20241103205331.GG237624@rocinante>
Date: Mon, 4 Nov 2024 05:53:31 +0900
From: Krzysztof Wilczyński <kw@...ux.com>
To: manivannan.sadhasivam@...aro.org
Cc: Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Jonathan Hunter <jonathanh@...dia.com>,
	Vidya Sagar <vidyas@...dia.com>, linux-pci@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Thierry Reding <treding@...dia.com>, linux-tegra@...r.kernel.org
Subject: Re: [PATCH 1/2] PCI: qcom-ep: Move controller cleanups to
 qcom_pcie_perst_deassert()

Hello,

> Currently, the endpoint cleanup function dw_pcie_ep_cleanup() and EPF
> deinit notify function pci_epc_deinit_notify() are called during the
> execution of qcom_pcie_perst_assert() i.e., when the host has asserted
> PERST#. But quickly after this step, refclk will also be disabled by the
> host.
> 
> All of the Qcom endpoint SoCs supported as of now depend on the refclk from
> the host for keeping the controller operational. Due to this limitation,
> any access to the hardware registers in the absence of refclk will result
> in a whole endpoint crash. Unfortunately, most of the controller cleanups
> require accessing the hardware registers (like eDMA cleanup performed in
> dw_pcie_ep_cleanup(), powering down MHI EPF etc...). So these cleanup
> functions are currently causing the crash in the endpoint SoC once host
> asserts PERST#.
> 
> One way to address this issue is by generating the refclk in the endpoint
> itself and not depending on the host. But that is not always possible as
> some of the endpoint designs do require the endpoint to consume refclk from
> the host (as I was told by the Qcom engineers).
> 
> So let's fix this crash by moving the controller cleanups to the start of
> the qcom_pcie_perst_deassert() function. qcom_pcie_perst_deassert() is
> called whenever the host has deasserted PERST# and it is guaranteed that
> the refclk would be active at this point. So at the start of this function
> (after enabling resources), the controller cleanup can be performed. Once
> finished, rest of the code execution for PERST# deassert can continue as
> usual.

Applied to controller/qcom, thank you!

[01/01] PCI: qcom-ep: Move controller cleanups to qcom_pcie_perst_deassert()
        https://git.kernel.org/pci/pci/c/7d7cf89b119a

	Krzysztof