linux-kernel - Re: [PATCH 1/5] phy: qcom: qmp-pcie: Skip PHY reset if already up

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Message-ID: <53f0c45f-7f5c-4abd-af84-cbb82d509872@linaro.org>
Date: Fri, 9 Jan 2026 14:10:49 +0100
From: Neil Armstrong <neil.armstrong@...aro.org>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
 Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Cc: Vinod Koul <vkoul@...nel.org>, Philipp Zabel <p.zabel@...gutronix.de>,
 Jingoo Han <jingoohan1@...il.com>, Manivannan Sadhasivam <mani@...nel.org>,
 Lorenzo Pieralisi <lpieralisi@...nel.org>,
 Krzysztof Wilczyński <kwilczynski@...nel.org>,
 Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
 linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
 linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH 1/5] phy: qcom: qmp-pcie: Skip PHY reset if already up

On 1/9/26 14:08, Dmitry Baryshkov wrote:
> On Fri, Jan 09, 2026 at 12:51:06PM +0530, Krishna Chaitanya Chundru wrote:
>> If the bootloader has already powered up the PCIe PHY, doing a full
>> reset and waiting for it to come up again slows down boot time.
> 
> How big is the delay caused by it?
> 
>>
>> Add a check for PHY status and skip the reset steps when the PHY is
>> already active. In this case, only enable the required resources during
>> power-on. This works alongside the existing logic that skips the init
>> sequence.
> 
> Can we end up in a state where the bootloader has mis-setup the link? Or
> the link going bad because of any glitch during the bootup?

Good question, can we add a module parameter to force a full reset of the PHY in case
the bootloader is buggy ?

> 
>>
>> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
>> ---
>>   drivers/phy/qualcomm/phy-qcom-qmp-pcie.c | 28 ++++++++++++++++++----------
>>   1 file changed, 18 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/phy/qualcomm/phy-qcom-qmp-pcie.c b/drivers/phy/qualcomm/phy-qcom-qmp-pcie.c
>> index 86b1b7e2da86a8675e3e48e90b782afb21cafd77..c93e613cf80b2612f0f225fa2125f78dbec1a33f 100644
>> --- a/drivers/phy/qualcomm/phy-qcom-qmp-pcie.c
>> +++ b/drivers/phy/qualcomm/phy-qcom-qmp-pcie.c
>> @@ -3153,6 +3153,7 @@ struct qmp_pcie {
>>   	const struct qmp_phy_cfg *cfg;
>>   	bool tcsr_4ln_config;
>>   	bool skip_init;
>> +	bool skip_reset;
>>   
>>   	void __iomem *serdes;
>>   	void __iomem *pcs;
>> @@ -4537,6 +4538,9 @@ static int qmp_pcie_init(struct phy *phy)
>>   		qphy_checkbits(pcs, cfg->regs[QPHY_START_CTRL], SERDES_START | PCS_START) &&
>>   		qphy_checkbits(pcs, cfg->regs[QPHY_PCS_POWER_DOWN_CONTROL], cfg->pwrdn_ctrl);
>>   
>> +	qmp->skip_reset = qmp->skip_init && !qphy_checkbits(pcs, cfg->regs[QPHY_PCS_STATUS],
> 
> It is definitely not a long-term state, there is no need to store it in
> qmp_pcie struct.
> 
>> +							    cfg->phy_status);
>> +
>>   	if (!qmp->skip_init && !cfg->tbls.serdes_num) {
>>   		dev_err(qmp->dev, "Init sequence not available\n");
>>   		return -ENODATA;
>> @@ -4560,13 +4564,15 @@ static int qmp_pcie_init(struct phy *phy)
>>   		}
>>   	}
>>   
>> -	ret = reset_control_assert(qmp->nocsr_reset);
>> -	if (ret) {
>> -		dev_err(qmp->dev, "no-csr reset assert failed\n");
>> -		goto err_assert_reset;
>> -	}
>> +	if (!qmp->skip_reset) {
>> +		ret = reset_control_assert(qmp->nocsr_reset);
>> +		if (ret) {
>> +			dev_err(qmp->dev, "no-csr reset assert failed\n");
>> +			goto err_assert_reset;
>> +		}
>>   
>> -	usleep_range(200, 300);
>> +		usleep_range(200, 300);
>> +	}
>>   
>>   	if (!qmp->skip_init) {
>>   		ret = reset_control_bulk_deassert(cfg->num_resets, qmp->resets);
>> @@ -4641,10 +4647,12 @@ static int qmp_pcie_power_on(struct phy *phy)
>>   	if (ret)
>>   		return ret;
>>   
>> -	ret = reset_control_deassert(qmp->nocsr_reset);
>> -	if (ret) {
>> -		dev_err(qmp->dev, "no-csr reset deassert failed\n");
>> -		goto err_disable_pipe_clk;
>> +	if (!qmp->skip_reset) {
>> +		ret = reset_control_deassert(qmp->nocsr_reset);
>> +		if (ret) {
>> +			dev_err(qmp->dev, "no-csr reset deassert failed\n");
>> +			goto err_disable_pipe_clk;
>> +		}
>>   	}
>>   
>>   	if (qmp->skip_init)
>>
>> -- 
>> 2.34.1
>>
>