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Message-ID: <ead761e1-2b48-4b9d-90cc-f63463a97f60@quicinc.com>
Date: Wed, 16 Jul 2025 12:23:54 +0530
From: Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
To: Manivannan Sadhasivam <mani@...nel.org>,
        Krishna Chaitanya Chundru
	<krishna.chundru@....qualcomm.com>
CC: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        Manivannan Sadhasivam
	<manivannan.sadhasivam@....qualcomm.com>,
        Lorenzo Pieralisi
	<lpieralisi@...nel.org>,
        Krzysztof WilczyƄski
	<kwilczynski@...nel.org>,
        Rob Herring <robh@...nel.org>, Bjorn Helgaas
	<bhelgaas@...gle.com>,
        <linux-arm-msm@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Johan Hovold
	<johan@...nel.org>
Subject: Re: [PATCH 2/2] PCI: qcom: Move qcom_pcie_icc_opp_update() to
 notifier callback



On 7/16/2025 12:16 PM, Manivannan Sadhasivam wrote:
> On Wed, Jul 16, 2025 at 10:24:23AM GMT, Krishna Chaitanya Chundru wrote:
>>
>>
>> On 7/15/2025 4:06 PM, Manivannan Sadhasivam wrote:
>>> On Tue, Jul 15, 2025 at 11:54:48AM GMT, Konrad Dybcio wrote:
>>>> On 7/14/25 8:01 PM, Manivannan Sadhasivam wrote:
>>>>> It allows us to group all the settings that need to be done when a PCI
>>>>> device is attached to the bus in a single place.
>>>>>
>>>>> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
>>>>> ---
>>>>>    drivers/pci/controller/dwc/pcie-qcom.c | 3 +--
>>>>>    1 file changed, 1 insertion(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
>>>>> index b4993642ed90915299e825e47d282b8175a78346..b364977d78a2c659f65f0f12ce4274601d20eaa6 100644
>>>>> --- a/drivers/pci/controller/dwc/pcie-qcom.c
>>>>> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
>>>>> @@ -1616,8 +1616,6 @@ static irqreturn_t qcom_pcie_global_irq_thread(int irq, void *data)
>>>>>    		pci_lock_rescan_remove();
>>>>>    		pci_rescan_bus(pp->bridge->bus);
>>>>>    		pci_unlock_rescan_remove();
>>>>> -
>>>>> -		qcom_pcie_icc_opp_update(pcie);
>>>>>    	} else {
>>>>>    		dev_WARN_ONCE(dev, 1, "Received unknown event. INT_STATUS: 0x%08x\n",
>>>>>    			      status);
>>>>> @@ -1765,6 +1763,7 @@ static int pcie_qcom_notify(struct notifier_block *nb, unsigned long action,
>>>>>    	switch (action) {
>>>>>    	case BUS_NOTIFY_BIND_DRIVER:
>>>>>    		qcom_pcie_enable_aspm(pdev);
>>>>> +		qcom_pcie_icc_opp_update(pcie);
>>>>
>>>> So I assume that we're not exactly going to do much with the device if
>>>> there isn't a driver for it, but I have concerns that since the link
>>>> would already be established(?), the icc vote may be too low, especially
>>>> if the user uses something funky like UIO
>>>>
>>>
>>> Hmm, that's a good point. Not enabling ASPM wouldn't have much consequence, but
>>> not updating OPP would be.
>>>
>>> Let me think of other ways to call these two APIs during the device addition. If
>>> there are no sane ways, I'll drop *this* patch.
>>>
>> How about using enable_device in host bridge, without pci_enable_device
>> call the endpoints can't start the transfers. May be we can use that.
>>
> 
> Q: Who is going to call pci_enable_device()?
> A: The PCI client driver
> 
> This is same as relying on BUS_NOTIFY_BIND_DRIVER notifier.
>
userspace can enable device using sysfs[1] without attaching
any kernel drivers.

[1] 
https://elixir.bootlin.com/linux/v6.16-rc6/source/drivers/pci/pci-sysfs.c#L315
- Krishna Chaitanya.

> - Mani
> 

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