linux-kernel - Re: [PATCH 2/2] phy: qcom-qmp-pcie: Add support for keeping refclk always on

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Date:   Mon, 6 Nov 2023 08:17:01 -0800
From:   Bjorn Andersson <andersson@...nel.org>
To:     Krishna chaitanya chundru <quic_krichai@...cinc.com>
Cc:     Andy Gross <agross@...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 2/2] phy: qcom-qmp-pcie: Add support for keeping refclk
 always on

On Mon, Nov 06, 2023 at 05:22:35PM +0530, Krishna chaitanya chundru 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
> 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

Double <space> ------------^^

> states.
> 
> Add a flag which indicates refclk is always supplied to endpoint.
> 

The patch itself look good, the problem description looks good, but if
you have an indication that the refclk "is always supplied to the
endpoint", then you don't have a problem with refclk and I don't think
you need this patch.

Something to the tune of "keep refclk always supplied to endpoint" seems
to more appropriately describe what this flag is doing.

> Signed-off-by: Krishna chaitanya chundru <quic_krichai@...cinc.com>
> ---
>  drivers/phy/qualcomm/phy-qcom-qmp-pcie.c | 21 +++++++++++++++++----
>  1 file changed, 17 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/phy/qualcomm/phy-qcom-qmp-pcie.c b/drivers/phy/qualcomm/phy-qcom-qmp-pcie.c
> index a63ca7424974..d7e377a7d96e 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
>  
> @@ -77,6 +79,7 @@ enum qphy_reg_layout {
>  	QPHY_START_CTRL,
>  	QPHY_PCS_STATUS,
>  	QPHY_PCS_POWER_DOWN_CONTROL,
> +	QPHY_PCS_ENDPOINT_REFCLK_CNTRL,
>  	/* Keep last to ensure regs_layout arrays are properly initialized */
>  	QPHY_LAYOUT_SIZE
>  };
> @@ -103,10 +106,11 @@ static const unsigned int sdm845_qhp_pciephy_regs_layout[QPHY_LAYOUT_SIZE] = {
>  };
>  
>  static const unsigned int pciephy_v4_regs_layout[QPHY_LAYOUT_SIZE] = {
> -	[QPHY_SW_RESET]			= QPHY_V4_PCS_SW_RESET,
> -	[QPHY_START_CTRL]		= QPHY_V4_PCS_START_CONTROL,
> -	[QPHY_PCS_STATUS]		= QPHY_V4_PCS_PCS_STATUS1,
> -	[QPHY_PCS_POWER_DOWN_CONTROL]	= QPHY_V4_PCS_POWER_DOWN_CONTROL,
> +	[QPHY_SW_RESET]				= QPHY_V4_PCS_SW_RESET,
> +	[QPHY_START_CTRL]			= QPHY_V4_PCS_START_CONTROL,
> +	[QPHY_PCS_STATUS]			= QPHY_V4_PCS_PCS_STATUS1,
> +	[QPHY_PCS_POWER_DOWN_CONTROL]		= QPHY_V4_PCS_POWER_DOWN_CONTROL,
> +	[QPHY_PCS_ENDPOINT_REFCLK_CNTRL]	= QPHY_V4_PCS_PCIE_ENDPOINT_REFCLK_CNTRL,
>  };
>  
>  static const unsigned int pciephy_v5_regs_layout[QPHY_LAYOUT_SIZE] = {
> @@ -2244,6 +2248,8 @@ struct qmp_pcie {
>  	struct phy *phy;
>  	int mode;
>  
> +	bool refclk_always_on;
> +
>  	struct clk_fixed_rate pipe_clk_fixed;
>  };
>  
> @@ -3159,6 +3165,10 @@ 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);
> @@ -3681,6 +3691,9 @@ 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");

Leave this line unwrapped, for readability.

Regards,
Bjorn

> +
>  	ret = phy_pipe_clk_register(qmp, np);
>  	if (ret)
>  		goto err_node_put;
> 
> -- 
> 2.42.0
>