Re: [V5,02/13] PCI: tegra194: Refactor LTSSM state polling on surprise down

[Jon Hunter <jonathanh@nvidia.com>]

On 08/02/2026 18:07, Manikanta Maddireddy wrote:
> From: Vidya Sagar <vidyas@nvidia.com>
> 
> On surprise down, LTSSM state transits from L0 -> Recovery.RcvrLock ->
> Recovery.RcvrSpeed -> Gen1 Recovery.RcvrLock -> Detect. Recovery.RcvrLock
> and Recovery.RcvrSpeed transit times are 24 msec and 48 msec respectively.
> So, the total time taken to transit from L0 to detect state is ~96 msec.
> Hence, increase the poll time to 120 msec.
> 
> Disable the LTSSM state after it transits to detect to avoid LTSSM
> toggling between polling and detect states.
> 
> tegra_pcie_dw_pme_turnoff() function is called in non-atomic context
> only, so use the non-atomic poll function.
> 
> Fixes: 56e15a238d92 ("PCI: tegra: Add Tegra194 PCIe support")
> Fixes: c57247f940e8 ("PCI: tegra: Add support for PCIe endpoint mode in Tegra194")

Two fixes tags here, we should only have one.

> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> Signed-off-by: Manikanta Maddireddy <mmaddireddy@nvidia.com>
> ---
> V5:
> * None
> 
> V4:
> * None
> 
> V3:
> * None
> 
> V2:
> * None
> 
>   drivers/pci/controller/dwc/pcie-tegra194.c | 55 +++++++++++++---------
>   1 file changed, 32 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-tegra194.c b/drivers/pci/controller/dwc/pcie-tegra194.c
> index 96d38571a7e7..4ac6b1cea13f 100644
> --- a/drivers/pci/controller/dwc/pcie-tegra194.c
> +++ b/drivers/pci/controller/dwc/pcie-tegra194.c
> @@ -137,7 +137,11 @@
>   #define APPL_DEBUG_PM_LINKST_IN_L0		0x11
>   #define APPL_DEBUG_LTSSM_STATE_MASK		GENMASK(8, 3)
>   #define APPL_DEBUG_LTSSM_STATE_SHIFT		3
> -#define LTSSM_STATE_PRE_DETECT			5
> +#define LTSSM_STATE_DETECT_QUIET		0x00
> +#define LTSSM_STATE_DETECT_ACT			0x08
> +#define LTSSM_STATE_PRE_DETECT_QUIET		0x28
> +#define LTSSM_STATE_DETECT_WAIT			0x30
> +#define LTSSM_STATE_L2_IDLE			0xa8
>   
>   #define APPL_RADM_STATUS			0xE4
>   #define APPL_PM_XMT_TURNOFF_STATE		BIT(0)
> @@ -201,7 +205,8 @@
>   #define PME_ACK_DELAY		100   /* 100 us */
>   #define PME_ACK_TIMEOUT		10000 /* 10 ms */
>   
> -#define LTSSM_TIMEOUT 50000	/* 50ms */
> +#define LTSSM_DELAY		10000	/* 10 ms */
> +#define LTSSM_TIMEOUT		120000	/* 120 ms */
>   
>   #define GEN3_GEN4_EQ_PRESET_INIT	5
>   
> @@ -1591,23 +1596,22 @@ static void tegra_pcie_dw_pme_turnoff(struct tegra_pcie_dw *pcie)
>   		data &= ~APPL_PINMUX_PEX_RST;
>   		appl_writel(pcie, data, APPL_PINMUX);
>   
> +		err = readl_poll_timeout(pcie->appl_base + APPL_DEBUG, data,
> +			((data & APPL_DEBUG_LTSSM_STATE_MASK) == LTSSM_STATE_DETECT_QUIET) ||
> +			((data & APPL_DEBUG_LTSSM_STATE_MASK) == LTSSM_STATE_DETECT_ACT) ||
> +			((data & APPL_DEBUG_LTSSM_STATE_MASK) == LTSSM_STATE_PRE_DETECT_QUIET) ||
> +			((data & APPL_DEBUG_LTSSM_STATE_MASK) == LTSSM_STATE_DETECT_WAIT),
> +			LTSSM_DELAY, LTSSM_TIMEOUT);
> +		if (err)
> +			dev_info(pcie->dev, "Link didn't go to detect state\n");
> +
>   		/*
> -		 * Some cards do not go to detect state even after de-asserting
> -		 * PERST#. So, de-assert LTSSM to bring link to detect state.
> +		 * Deassert LTSSM state to stop the state toggling between
> +		 * polling and detect.
>   		 */
>   		data = readl(pcie->appl_base + APPL_CTRL);
>   		data &= ~APPL_CTRL_LTSSM_EN;
>   		writel(data, pcie->appl_base + APPL_CTRL);
> -
> -		err = readl_poll_timeout_atomic(pcie->appl_base + APPL_DEBUG,
> -						data,
> -						((data &
> -						APPL_DEBUG_LTSSM_STATE_MASK) >>
> -						APPL_DEBUG_LTSSM_STATE_SHIFT) ==
> -						LTSSM_STATE_PRE_DETECT,
> -						1, LTSSM_TIMEOUT);
> -		if (err)
> -			dev_info(pcie->dev, "Link didn't go to detect state\n");
>   	}
>   	/*
>   	 * DBI registers may not be accessible after this as PLL-E would be
> @@ -1681,19 +1685,24 @@ static void pex_ep_event_pex_rst_assert(struct tegra_pcie_dw *pcie)
>   	if (pcie->ep_state == EP_STATE_DISABLED)
>   		return;
>   
> -	/* Disable LTSSM */
> +	ret = readl_poll_timeout(pcie->appl_base + APPL_DEBUG, val,
> +		((val & APPL_DEBUG_LTSSM_STATE_MASK) == LTSSM_STATE_DETECT_QUIET) ||
> +		((val & APPL_DEBUG_LTSSM_STATE_MASK) == LTSSM_STATE_DETECT_ACT) ||
> +		((val & APPL_DEBUG_LTSSM_STATE_MASK) == LTSSM_STATE_PRE_DETECT_QUIET) ||
> +		((val & APPL_DEBUG_LTSSM_STATE_MASK) == LTSSM_STATE_DETECT_WAIT) ||
> +		((val & APPL_DEBUG_LTSSM_STATE_MASK) == LTSSM_STATE_L2_IDLE),
> +		LTSSM_DELAY, LTSSM_TIMEOUT);
> +	if (ret)
> +		dev_err(pcie->dev, "LTSSM state: 0x%x timeout: %d\n", val, ret);
> +
> +	/*
> +	 * Deassert LTSSM state to stop the state toggling between
> +	 * polling and detect.
> +	 */
>   	val = appl_readl(pcie, APPL_CTRL);
>   	val &= ~APPL_CTRL_LTSSM_EN;
>   	appl_writel(pcie, val, APPL_CTRL);
>   
> -	ret = readl_poll_timeout(pcie->appl_base + APPL_DEBUG, val,
> -				 ((val & APPL_DEBUG_LTSSM_STATE_MASK) >>
> -				 APPL_DEBUG_LTSSM_STATE_SHIFT) ==
> -				 LTSSM_STATE_PRE_DETECT,
> -				 1, LTSSM_TIMEOUT);
> -	if (ret)
> -		dev_err(pcie->dev, "Failed to go Detect state: %d\n", ret);
> -
>   	reset_control_assert(pcie->core_rst);
>   
>   	tegra_pcie_disable_phy(pcie);

-- 
nvpublic