linux-kernel - Re: [PATCH v2 3/3] phy: qcom-qmp-pcie: Add support for keeping refclk always on

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Message-ID: <CAA8EJpp1ObZjmX65TctoPo7ywvFBguFND2LcmTq3Dhcj=3vstg@mail.gmail.com>
Date:   Tue, 7 Nov 2023 15:08:41 +0200
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Krishna chaitanya chundru <quic_krichai@...cinc.com>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Vinod Koul <vkoul@...nel.org>,
        Kishon Vijay Abraham I <kishon@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        quic_vbadigan@...cinc.com, quic_ramkri@...cinc.com,
        quic_nitegupt@...cinc.com, quic_skananth@...cinc.com,
        quic_vpernami@...cinc.com, quic_parass@...cinc.com
Subject: Re: [PATCH v2 3/3] phy: qcom-qmp-pcie: Add support for keeping refclk
 always on

On Tue, 7 Nov 2023 at 14:26, Krishna chaitanya chundru
<quic_krichai@...cinc.com> wrote:
>
> In PCIe low power states like L1.1 or L1.2 the phy will stop
> supplying refclk to endpoint. If endpoint asserts clkreq to bring
> back link L0, then RC needs to provide refclk to endpoint.
>
> If there is some issues in platform with clkreq signal propagation

Nit: there are

I'd rephrase this in the following way:

Some platforms (e.g. ABC DEF) fail to drive the clkreq signal to the
host (because it is unconnected ?). Due to that...

Other than that:

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

> to host and due to that host will not send refclk which results PCIe link
> down. For those platforms phy needs to provide refclk even in low power
> states.
>
> Add a flag to keep refclk always supplied to endpoint.
>
> Signed-off-by: Krishna chaitanya chundru <quic_krichai@...cinc.com>
> ---
>  drivers/phy/qualcomm/phy-qcom-qmp-pcie.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
>
> diff --git a/drivers/phy/qualcomm/phy-qcom-qmp-pcie.c b/drivers/phy/qualcomm/phy-qcom-qmp-pcie.c
> index 74d03d217ff2..a8d6d69e3f74 100644
> --- a/drivers/phy/qualcomm/phy-qcom-qmp-pcie.c
> +++ b/drivers/phy/qualcomm/phy-qcom-qmp-pcie.c
> @@ -43,6 +43,8 @@
>  /* QPHY_PCS_STATUS bit */
>  #define PHYSTATUS                              BIT(6)
>  #define PHYSTATUS_4_20                         BIT(7)
> +/* PCS_PCIE_ENDPOINT_REFCLK_CNTRL */
> +#define EPCLK_ALWAYS_ON_EN                     BIT(6)
>
>  #define PHY_INIT_COMPLETE_TIMEOUT              10000
>
> @@ -2264,6 +2266,8 @@ struct qmp_pcie {
>         struct phy *phy;
>         int mode;
>
> +       bool refclk_always_on;
> +
>         struct clk_fixed_rate pipe_clk_fixed;
>  };
>
> @@ -3179,6 +3183,10 @@ static void qmp_pcie_init_registers(struct qmp_pcie *qmp, const struct qmp_phy_c
>         qmp_pcie_configure(pcs, tbls->pcs, tbls->pcs_num);
>         qmp_pcie_configure(pcs_misc, tbls->pcs_misc, tbls->pcs_misc_num);
>
> +       if (qmp->refclk_always_on && cfg->regs[QPHY_PCS_ENDPOINT_REFCLK_CNTRL])
> +               qphy_setbits(pcs_misc, cfg->regs[QPHY_PCS_ENDPOINT_REFCLK_CNTRL],
> +                            EPCLK_ALWAYS_ON_EN);
> +
>         if (cfg->lanes >= 4 && qmp->tcsr_4ln_config) {
>                 qmp_pcie_configure(serdes, cfg->serdes_4ln_tbl, cfg->serdes_4ln_num);
>                 qmp_pcie_init_port_b(qmp, tbls);
> @@ -3701,6 +3709,12 @@ static int qmp_pcie_probe(struct platform_device *pdev)
>         if (ret)
>                 goto err_node_put;
>
> +       qmp->refclk_always_on = of_property_read_bool(dev->of_node, "qcom,refclk-always-on");
> +       if (qmp->refclk_always_on && !qmp->cfg->regs[QPHY_PCS_ENDPOINT_REFCLK_CNTRL]) {
> +               dev_err(dev, "refclk is always on is present but refclk cntrl offset is not present\n");
> +               goto err_node_put;
> +       }
> +
>         ret = phy_pipe_clk_register(qmp, np);
>         if (ret)
>                 goto err_node_put;
>
> --
> 2.42.0
>
>


-- 
With best wishes
Dmitry