Re: [PATCH 3/3] PCI: tegra194: Notify Endpoint functions on PERST# assert

[Manivannan Sadhasivam]

On Wed, Sep 23, 2026 at 12:55:54PM +0530, Manikanta Maddireddy wrote:
> Tegra Endpoint mode powers the controller down when the host asserts
> PERST#. EPF drivers must be told about link down before that happens,
> otherwise remove while PERST# is asserted can free EPC resources while
> EPF work is still active.
> 
> Use pci_epc_linkdown() directly in the PERST# assert path. It is a
> software-only EPF notification

Not entirely true. The EPF drivers can still access the hardware registers in
the link_down() callback. But most likely they won't access any DBI registers,
so that access may still be OK without REFCLK.

> and avoids dw_pcie_ep_linkdown(), which
> reinitializes non-sticky DWC registers and touches DBI while the host
> REFCLK may be disappearing.
> 
> Keep pci_epc_deinit_notify() in the PERST# deassert path, after core
> reset is deasserted, because EPF deinit callbacks can clear BARs and
> therefore need register access. If remove runs while the controller is
> already powered down, pex_ep_event_pex_rst_assert() returns because
> ep_state is disabled; that is safe because the link-down notification
> was sent at the earlier PERST# assert.
> 
> The final dw_pcie_ep_deinit() does not require Tegra register access
> today: Tegra uses its own MSI-X address-match window instead of the
> DWC MSI iATU, and the supported DTs do not register a DWC eDMA device.
> 

Is the last paragraph related to this patch?

> Signed-off-by: Manikanta Maddireddy <mmaddireddy@xxxxxxxxxx>
> ---
>  drivers/pci/controller/dwc/pcie-tegra194.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-tegra194.c b/drivers/pci/controller/dwc/pcie-tegra194.c
> index dd3f4c30ba52..3e9d46850a78 100644
> --- a/drivers/pci/controller/dwc/pcie-tegra194.c
> +++ b/drivers/pci/controller/dwc/pcie-tegra194.c
> @@ -1724,6 +1724,7 @@ static int tegra_pcie_config_rp(struct tegra_pcie_dw *pcie)
>  
>  static void pex_ep_event_pex_rst_assert(struct tegra_pcie_dw *pcie)
>  {
> +	struct dw_pcie_ep *ep = &pcie->pci.ep;
>  	u32 val;
>  	int ret;
>  
> @@ -1745,6 +1746,8 @@ static void pex_ep_event_pex_rst_assert(struct tegra_pcie_dw *pcie)
>  	if (ret)
>  		dev_info(pcie->dev, "LTSSM state: 0x%x detect timeout: %d\n", val, ret);
>  
> +	pci_epc_linkdown(ep->epc);
> +
>  	/*
>  	 * Deassert LTSSM state to stop the state toggling between
>  	 * Polling and Detect.
> @@ -1913,7 +1916,7 @@ static void pex_ep_event_pex_rst_deassert(struct tegra_pcie_dw *pcie)
>  	}
>  
>  	/* Perform cleanup that requires refclk and core reset deasserted */
> -	pci_epc_deinit_notify(pcie->pci.ep.epc);
> +	pci_epc_deinit_notify(ep->epc);

Unrelated change.

- Mani

-- 
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