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

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Message-ID: <996d4368-57d9-43cf-381b-4d4c5ded9fdc@quicinc.com>
Date:   Tue, 7 Nov 2023 15:23:00 +0530
From:   Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
To:     Bjorn Andersson <andersson@...nel.org>
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 11/6/2023 9:47 PM, Bjorn Andersson wrote:
> 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> ------------^^
ACK
>> 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.
Sure I will change it in my next patch.
>> 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

sure I will update this in next patch.

- Krishna Chaitanya.

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