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

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Date:   Tue, 8 Dec 2020 11:42:10 +0530
From:   Vidya Sagar <vidyas@...dia.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
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



On 12/8/2020 2:07 AM, Bjorn Helgaas wrote:
> External email: Use caution opening links or attachments
> 
> 
> [+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?
This is a Tegra194 specific issue.

Thanks,
Vidya Sagar
> 
>> 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
>>