linux-kernel - Re: [PATCH 2/2] PCI: tegra194: Move controller cleanups to pex_ep_event_pex_rst

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Message-ID: <20241103205515.GH237624@rocinante>
Date: Mon, 4 Nov 2024 05:55:15 +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 2/2] PCI: tegra194: Move controller cleanups to
 pex_ep_event_pex_rst_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 pex_ep_event_pex_rst_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 tegra194 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(), etc...). So these cleanup
> functions can cause 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.
> 
> So let's fix this crash by moving the controller cleanups to the start of
> the pex_ep_event_pex_rst_deassert() function. This function 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/tegra194, thank you!

[01/01] PCI: tegra194: Move controller cleanups to pex_ep_event_pex_rst_deassert()
        https://git.kernel.org/pci/pci/c/40e2125381dc

	Krzysztof