linux-kernel - Re: [PATCH V5 5/5] PCI: tegra: Disable LTSSM during L2 entry

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Date:   Mon, 7 Dec 2020 14:37:30 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Vidya Sagar <vidyas@...dia.com>
Cc:     lorenzo.pieralisi@....com, robh+dt@...nel.org, bhelgaas@...gle.com,
        thierry.reding@...il.com, jonathanh@...dia.com,
        amanharitsh123@...il.com, dinghao.liu@....edu.cn, kw@...ux.com,
        linux-pci@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org, kthota@...dia.com,
        mmaddireddy@...dia.com, sagar.tv@...il.com,
        Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>
Subject: Re: [PATCH V5 5/5] PCI: tegra: Disable LTSSM during L2 entry

[+cc Jingoo, Gustavo]

On Thu, Dec 03, 2020 at 07:04:51PM +0530, Vidya Sagar wrote:
> PCIe cards like Marvell SATA controller and some of the Samsung NVMe
> drives don't support taking the link to L2 state. When the link doesn't
> go to L2 state, Tegra194 requires the LTSSM to be disabled to allow PHY
> to start the next link up process cleanly during suspend/resume sequence.
> Failing to disable LTSSM results in the PCIe link not coming up in the
> next resume cycle.

Is this a Tegra194-specific issue, or will other DWC-based controllers
need a similar change?

> Tested-by: Thierry Reding <treding@...dia.com>
> Signed-off-by: Vidya Sagar <vidyas@...dia.com>
> Acked-by: Thierry Reding <treding@...dia.com>
> ---
> V5:
> * Added Tested-by and Acked-by from Thierry Reding
> 
> V4:
> * New patch in this series
> 
>  drivers/pci/controller/dwc/pcie-tegra194.c | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-tegra194.c b/drivers/pci/controller/dwc/pcie-tegra194.c
> index f4109d71f20b..5597b2a49598 100644
> --- a/drivers/pci/controller/dwc/pcie-tegra194.c
> +++ b/drivers/pci/controller/dwc/pcie-tegra194.c
> @@ -1506,6 +1506,14 @@ static void tegra_pcie_dw_pme_turnoff(struct tegra_pcie_dw *pcie)
>  		data &= ~APPL_PINMUX_PEX_RST;
>  		appl_writel(pcie, data, APPL_PINMUX);
>  
> +		/*
> +		 * Some cards do not go to detect state even after de-asserting
> +		 * PERST#. So, de-assert LTSSM to bring link to detect state.
> +		 */
> +		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 &
> @@ -1513,14 +1521,8 @@ static void tegra_pcie_dw_pme_turnoff(struct tegra_pcie_dw *pcie)
>  						APPL_DEBUG_LTSSM_STATE_SHIFT) ==
>  						LTSSM_STATE_PRE_DETECT,
>  						1, LTSSM_TIMEOUT);
> -		if (err) {
> +		if (err)
>  			dev_info(pcie->dev, "Link didn't go to detect state\n");
> -		} else {
> -			/* Disable LTSSM after link is in detect state */
> -			data = appl_readl(pcie, APPL_CTRL);
> -			data &= ~APPL_CTRL_LTSSM_EN;
> -			appl_writel(pcie, data, APPL_CTRL);
> -		}
>  	}
>  	/*
>  	 * DBI registers may not be accessible after this as PLL-E would be
> -- 
> 2.17.1
>