linux-kernel - Re: [PATCH v3 1/2] PCI: pciehp: Add support for async hotplug with native AER and DPC/EDR

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Date:   Thu, 22 Jun 2023 14:02:03 -0700
From:   Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>, oohall@...il.com,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Yazen Ghannam <yazen.ghannam@....com>,
        Fontenot Nathan <Nathan.Fontenot@....com>
Subject: Re: [PATCH v3 1/2] PCI: pciehp: Add support for async hotplug with
 native AER and DPC/EDR

On 6/22/2023 2:04 AM, Lukas Wunner wrote:
> On Wed, Jun 21, 2023 at 06:51:51PM +0000, Smita Koralahalli wrote:
>> --- a/drivers/pci/pcie/dpc.c
>> +++ b/drivers/pci/pcie/dpc.c
>> @@ -292,10 +292,68 @@ void dpc_process_error(struct pci_dev *pdev)
>>   	}
>>   }
>>   
>> +static void pci_clear_surpdn_errors(struct pci_dev *pdev)
>> +{
>> +	u16 reg16;
>> +	u32 reg32;
>> +
>> +	pci_read_config_dword(pdev, pdev->dpc_cap + PCI_EXP_DPC_RP_PIO_STATUS, &reg32);
>> +	pci_write_config_dword(pdev, pdev->dpc_cap + PCI_EXP_DPC_RP_PIO_STATUS, reg32);
> 
> Make this read+write conditional on "if (pdev->dpc_rp_extensions)"
> as the register otherwise doesn't exist.

I'm checking for pdev->dpc_rpc_extensions inside 
dpc_handle_surprise_removal() before calling pci_clear_surpdn_errors(). 
Should I recheck it once again here?

> 
> Wrap to 80 chars per line.

Okay.

> 
> 
>> +	pci_read_config_word(pdev, PCI_STATUS, &reg16);
>> +	pci_write_config_word(pdev, PCI_STATUS, reg16);
>> +
>> +	pcie_capability_write_word(pdev, PCI_EXP_DEVSTA, PCI_EXP_DEVSTA_FED);
>> +}
> 
> A code comment might be useful here saying that in practice,
> Surprise Down errors have been observed to also set error bits
> in the Status Register as well as the Fatal Error Detected bit
> in the Device Status Register.

And probably move this code comment below to where this function is 
called inside dpc_handle_surprise_removal()..?

> 
> 
>> +static void dpc_handle_surprise_removal(struct pci_dev *pdev)
>> +{
> 
> I'm wondering if we also need
> 
> 	if (!pcie_wait_for_link(pdev, false)) {
> 		pci_info(pdev, "Data Link Layer Link Active not cleared in 1000 msec\n");
> 		goto out;
> 	}
> 
> here, similar to dpc_reset_link() and in accordance with PCIe r6.1
> sec 6.2.11:
> 
> 	"To ensure that the LTSSM has time to reach the Disabled state
> 	or at least to bring the Link down under a variety of error
> 	conditions, software must leave the Downstream Port in DPC
> 	until the Data Link Layer Link Active bit in the Link Status
> 	Register reads 0b; otherwise, the result is undefined."

And include the above comment in code..
> 
> 
>> +	if (pdev->dpc_rp_extensions && dpc_wait_rp_inactive(pdev)) {
>> +		pci_err(pdev, "failed to retrieve DPC root port on async remove\n");
>> +		goto out;
>> +	}
> 
> I don't think pci_err() is needed here as dpc_wait_rp_inactive()
> already emits a message.  (I think I mistakenly gave the advice
> to emit an error here in an earlier review comment -- sorry!)

:)

Will take care of other comments below as well.

Thanks,
Smita

>>   
>>   	/* We configure DPC so it only triggers on ERR_FATAL */
>> -- 
>> 2.17.1
>>