Re: [PATCH v2 07/10] PCI: tegra194: Always disable Tegra234 Endpoint L1.2

[Frank Li]

On Wed, Oct 21, 2026 at 11:43:46AM +0530, Manikanta Maddireddy wrote:
> Tegra234 Endpoint mode must not advertise L1.2 because exiting L1.2 can
> bring the link down. That hardware workaround is required regardless of
> whether the endpoint kernel is built with CONFIG_PCIEASPM.
>
> Move the L1.2 capability masking out of init_host_aspm(), which is compiled
> out when CONFIG_PCIEASPM is disabled, and apply it from the common
> initialization paths.
>
> Fixes: f59df1d9e6bd ("PCI: tegra194: Disable L1.2 capability of Tegra234 EP")
> Signed-off-by: Manikanta Maddireddy <mmaddireddy@xxxxxxxxxx>
> ---

Reviewed-by: Frank Li <Frank.Li@xxxxxxx>

> Changes V1 -> V2: None
>
>  drivers/pci/controller/dwc/pcie-tegra194.c | 47 +++++++++++++---------
>  1 file changed, 28 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/pci/controller/dwc/pcie-tegra194.c b/drivers/pci/controller/dwc/pcie-tegra194.c
> index 7c349478556d..0e6224b6751d 100644
> --- a/drivers/pci/controller/dwc/pcie-tegra194.c
> +++ b/drivers/pci/controller/dwc/pcie-tegra194.c
> @@ -611,6 +611,33 @@ static struct pci_ops tegra_pci_ops = {
>  	.write = tegra_pcie_dw_wr_own_conf,
>  };
>
> +/*
> + * Disable L1.2 capability advertisement for Tegra234 Endpoint mode.
> + * Tegra234 has a hardware bug where during L1.2 exit, the UPHY PLL is
> + * powered up immediately without waiting for REFCLK to stabilize. This causes
> + * the PLL to fail to lock to the correct frequency, resulting in PCIe link
> + * loss. Since there is no hardware fix available, prevent the Endpoint from
> + * advertising L1.2 support so the host will not attempt to enter L1.2 with
> + * this Endpoint.
> + */
> +static void tegra_pcie_disable_ep_l1_2(struct tegra_pcie_dw *pcie)
> +{
> +	struct dw_pcie *pci = &pcie->pci;
> +	u32 l1ss, val;
> +
> +	if (!pcie->of_data->disable_l1_2 ||
> +	    pcie->of_data->mode != DW_PCIE_EP_TYPE)
> +		return;
> +
> +	l1ss = dw_pcie_find_ext_capability(pci, PCI_EXT_CAP_ID_L1SS);
> +	if (!l1ss)
> +		return;
> +
> +	val = dw_pcie_readl_dbi(pci, l1ss + PCI_L1SS_CAP);
> +	val &= ~(PCI_L1SS_CAP_PCIPM_L1_2 | PCI_L1SS_CAP_ASPM_L1_2);
> +	dw_pcie_writel_dbi(pci, l1ss + PCI_L1SS_CAP, val);
> +}
> +
>  #if defined(CONFIG_PCIEASPM)
>  static inline u32 event_counter_prog(struct tegra_pcie_dw *pcie, u32 event)
>  {
> @@ -694,25 +721,6 @@ static void init_host_aspm(struct tegra_pcie_dw *pcie)
>
>  		if (pcie->supports_clkreq)
>  			pci->l1ss_support = true;
> -
> -		/*
> -		 * Disable L1.2 capability advertisement for Tegra234 Endpoint
> -		 * mode. Tegra234 has a hardware bug where during L1.2 exit,
> -		 * the UPHY PLL is powered up immediately without waiting for
> -		 * REFCLK to stabilize. This causes the PLL to fail to lock to
> -		 * the correct frequency, resulting in PCIe link loss. Since
> -		 * there is no hardware fix available, prevent the Endpoint
> -		 * from advertising L1.2 support by clearing the L1.2 bits in
> -		 * the L1 PM Substates Capabilities register. This ensures the
> -		 * host will not attempt to enter L1.2 with this Endpoint.
> -		 */
> -		if (pcie->of_data->disable_l1_2 &&
> -		    pcie->of_data->mode == DW_PCIE_EP_TYPE) {
> -			val = dw_pcie_readl_dbi(pci, l1ss + PCI_L1SS_CAP);
> -			val &= ~(PCI_L1SS_CAP_PCIPM_L1_2 |
> -				 PCI_L1SS_CAP_ASPM_L1_2);
> -			dw_pcie_writel_dbi(pci, l1ss + PCI_L1SS_CAP, val);
> -		}
>  	}
>
>  	/* Program L0s and L1 entrance latencies */
> @@ -1903,6 +1911,7 @@ static void pex_ep_event_pex_rst_deassert(struct tegra_pcie_dw *pcie)
>  	config_gen3_gen4_eq_presets(pcie);
>
>  	init_host_aspm(pcie);
> +	tegra_pcie_disable_ep_l1_2(pcie);
>
>  	if (!pcie->of_data->has_l1ss_exit_fix) {
>  		val = dw_pcie_readl_dbi(pci, GEN3_CTRL);
> --
> 2.34.1
>