linux-kernel - Re: [PATCH] PCI: Add device-specific reset for Kunpeng virtual functions

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Message-ID: <5ed27a49-a437-66b1-8835-c3335edde07c@huawei.com>
Date: Fri, 18 Jul 2025 15:21:30 +0800
From: Weili Qian <qianweili@...wei.com>
To: Bjorn Helgaas <helgaas@...nel.org>
CC: <bhelgaas@...gle.com>, <linux-pci@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <liulongfang@...wei.com>, Hui Wang
	<hui.wang@...onical.com>
Subject: Re: [PATCH] PCI: Add device-specific reset for Kunpeng virtual
 functions



On 2025/7/15 3:19, Bjorn Helgaas wrote:
> [+cc Hui]
> 
> On Sat, Jul 12, 2025 at 07:30:28PM +0800, Weili Qian wrote:
>> Prior to commit d591f6804e7e ("PCI: Wait for device readiness with
>> Configuration RRS"), pci_dev_wait() polls PCI_COMMAND register until
>> its value is not ~0(i.e., PCI_ERROR_RESPONSE). After d591f6804e7e,
>> if the Configuration Request Retry Status Software Visibility (RRS SV)
>> is enabled, pci_dev_wait() polls PCI_VENDOR_ID register until its value
>> is not the reserved Vendor ID value 0x0001.
>>
>> On Kunpeng accelerator devices, RRS SV is enabled. However,
>> when the virtual function's FLR (Function Level Reset) is not
>> ready, the pci_dev_wait() reads the PCI_VENDOR_ID register and gets
>> the value 0xffff instead of 0x0001. It then incorrectly assumes this
>> is a valid Vendor ID and concludes the device is ready, returning
>> successfully. In reality, the function may not be fully ready, leading
>> to the device becoming unavailable.
>>
>> A 100ms wait period is already implemented before calling pci_dev_wait().
>> In most cases, FLR completes within 100ms. However, to eliminate the
>> risk of function being unavailable due to an incomplete FLR, a
>> device-specific reset is added. After pcie_flr(), the function continues
>> to poll PCI_COMMAND register until its value is no longer ~0.
> 
> As far as I can tell, there's nothing specific to Kungpeng devices
> here.  We've seen a similar issue with Intel NVMe devices [1], and I
> don't want a whole mess of quirks and device-specific reset methods.
> 
> We need some sort of generic solution for this.  My understanding was
> that if devices are not ready 100ms after a reset, they are required
> to respond with RRS.  Maybe these devices are defective.  Or maybe my
> understanding is incorrect.  Either way, I think we should at least
> check for a PCIe error before assuming that 0xffff is a valid
> response.

A generic solution for this would be even better.

I tested the patch in [1], but it did not resolve the issue. According to the PCIe specification(e.g.,
Section 7.5.1 PCI-Compatible Configuration Registers), the Vendor ID and Device ID for VFs are 0xffff.
However, if VFs cannot respond using the RRS mechanism, the pci_dev_wait() function reads the PCI_VENDOR_ID
register and gets the value 0xffffffff. This value is considered an error on PCIe, causing pci_dev_wait()
to continuously poll the register until a timeout occurs.

Thanks,
Weili
> 
> [1] https://lore.kernel.org/linux-pci/20250611101442.387378-1-hui.wang@canonical.com/
> 
>> Fixes: d591f6804e7e ("PCI: Wait for device readiness with Configuration RRS")
>> Signed-off-by: Weili Qian <qianweili@...wei.com>
>> ---
>>  drivers/pci/quirks.c | 36 ++++++++++++++++++++++++++++++++++++
>>  1 file changed, 36 insertions(+)
>>
>> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
>> index d7f4ee634263..1df1756257d2 100644
>> --- a/drivers/pci/quirks.c
>> +++ b/drivers/pci/quirks.c
>> @@ -4205,6 +4205,36 @@ static int reset_hinic_vf_dev(struct pci_dev *pdev, bool probe)
>>  	return 0;
>>  }
>>  
>> +#define KUNPENG_OPERATION_WAIT_CNT	3000
>> +#define KUNPENG_RESET_WAIT_TIME		20
>> +
>> +/* Device-specific reset method for Kunpeng accelerator virtual functions */
>> +static int reset_kunpeng_acc_vf_dev(struct pci_dev *pdev, bool probe)
>> +{
>> +	u32 wait_cnt = 0;
>> +	u32 cmd;
>> +
>> +	if (probe)
>> +		return 0;
>> +
>> +	pcie_flr(pdev);
>> +
>> +	do {
>> +		pci_read_config_dword(pdev, PCI_COMMAND, &cmd);
>> +		if (!PCI_POSSIBLE_ERROR(cmd))
>> +			break;
>> +
>> +		if (++wait_cnt > KUNPENG_OPERATION_WAIT_CNT) {
>> +			pci_warn(pdev, "wait for FLR ready timeout; giving up\n");
>> +			return -ENOTTY;
>> +		}
>> +
>> +		msleep(KUNPENG_RESET_WAIT_TIME);
>> +	} while (true);
>> +
>> +	return 0;
>> +}
>> +
>>  static const struct pci_dev_reset_methods pci_dev_reset_methods[] = {
>>  	{ PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_INTEL_82599_SFP_VF,
>>  		 reset_intel_82599_sfp_virtfn },
>> @@ -4220,6 +4250,12 @@ static const struct pci_dev_reset_methods pci_dev_reset_methods[] = {
>>  		reset_chelsio_generic_dev },
>>  	{ PCI_VENDOR_ID_HUAWEI, PCI_DEVICE_ID_HINIC_VF,
>>  		reset_hinic_vf_dev },
>> +	{ PCI_VENDOR_ID_HUAWEI, PCI_DEVICE_ID_HUAWEI_ZIP_VF,
>> +		reset_kunpeng_acc_vf_dev },
>> +	{ PCI_VENDOR_ID_HUAWEI, PCI_DEVICE_ID_HUAWEI_SEC_VF,
>> +		reset_kunpeng_acc_vf_dev },
>> +	{ PCI_VENDOR_ID_HUAWEI, PCI_DEVICE_ID_HUAWEI_HPRE_VF,
>> +		reset_kunpeng_acc_vf_dev },
>>  	{ 0 }
>>  };
>>  
>> -- 
>> 2.33.0
>>
> .
>