linux-kernel - Re: [RFC PATCH 3/6] PCI/AER: Enable RCEC to report internal error for CXL root port

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Date: Tue, 16 Apr 2024 15:27:27 +0800
From: "Li, Ming" <ming4.li@...el.com>
To: Terry Bowman <Terry.Bowman@....com>, <dan.j.williams@...el.com>,
	<rrichter@....com>
CC: <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 3/6] PCI/AER: Enable RCEC to report internal error for
 CXL root port

On 3/26/2024 3:42 AM, Terry Bowman wrote:
> Hi Li, 
> 
> I added comments below.
> 
> On 3/13/24 03:35, Li Ming wrote:
>> Per CXl r3.1 section 12.2.2, CXL.cachemem protocol erros detected by CXL
>> root port could be logged in RCEC AER Extended Capability as
>> PCI_ERR_UNC_INTN or PCI_ERR_COR_INTERNAL. Unmask these errors for that
>> case.
>>
>> Signed-off-by: Li Ming <ming4.li@...el.com>
>> ---
>>  drivers/pci/pcie/aer.c | 24 +++++++++++++++++-------
>>  1 file changed, 17 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
>> index 42a3bd35a3e1..364c74e47273 100644
>> --- a/drivers/pci/pcie/aer.c
>> +++ b/drivers/pci/pcie/aer.c
>> @@ -985,7 +985,7 @@ static bool cxl_error_is_native(struct pci_dev *dev)
>>  {
>>  	struct pci_host_bridge *host = pci_find_host_bridge(dev->bus);
>>  
>> -	return (pcie_ports_native || host->native_aer);
>> +	return (pcie_ports_native || host->native_aer) && host->is_cxl;
>>  }
>>  
>>  static bool is_internal_error(struct aer_err_info *info)
>> @@ -1041,8 +1041,13 @@ static int handles_cxl_error_iter(struct pci_dev *dev, void *data)
>>  {
>>  	bool *handles_cxl = data;
>>  
>> -	if (!*handles_cxl)
>> -		*handles_cxl = is_cxl_mem_dev(dev) && cxl_error_is_native(dev);
>> +	if (!*handles_cxl && cxl_error_is_native(dev)) {
>> +		if (pci_pcie_type(dev) == PCI_EXP_TYPE_RC_END &&
>> +		    dev->rcec && is_cxl_mem_dev(dev))
>> +			*handles_cxl = true;
>> +		if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT)
>> +			*handles_cxl = true;
>> +	}
> I understand a root port can be found under an RCEC. It's possible. But, does the downstream 
> root port forward AER to the upstream RCEC? My understanding is AER is handled and processed
> at the first root port/RCEC upstream from the device/RCH/USP/DSP.
>  
> Regards,
> Terry
> 

CXL r3.1 section 12.2.2 mentions this:

"If the CXL.cachemem protocol errors detected by a CXL root port are logged as
CIEs or UIEs in an RCEC’s AER Extended Capability, it is recommended that the System
Firmware populate an RDPAS record (see Section 9.18.1.5) to establish the association
between the RCEC and the root port."

I think it means that CXL root port is possible to forward its AER to RCEC.

Thanks
Ming

>>  
>>  	/* Non-zero terminates iteration */
>>  	return *handles_cxl;
>> @@ -1054,13 +1059,18 @@ static bool handles_cxl_errors(struct pci_dev *rcec)
>>  
>>  	if (pci_pcie_type(rcec) == PCI_EXP_TYPE_RC_EC &&
>>  	    pcie_aer_is_native(rcec))
>> -		pcie_walk_rcec(rcec, handles_cxl_error_iter, &handles_cxl);
>> +		pcie_walk_rcec_all(rcec, handles_cxl_error_iter, &handles_cxl);
>>  
>>  	return handles_cxl;
>>  }
>>  
>> -static void cxl_rch_enable_rcec(struct pci_dev *rcec)
>> +static void cxl_enable_rcec(struct pci_dev *rcec)
>>  {
>> +	/*
>> +	 * Enable RCEC's internal error report for two cases:
>> +	 * 1. RCiEP detected CXL.cachemem protocol errors
>> +	 * 2. CXL root port detected CXL.cachemem protocol errors.
>> +	 */
>>  	if (!handles_cxl_errors(rcec))
>>  		return;
>>  
>> @@ -1069,7 +1079,7 @@ static void cxl_rch_enable_rcec(struct pci_dev *rcec)
>>  }
>>  
>>  #else
>> -static inline void cxl_rch_enable_rcec(struct pci_dev *dev) { }
>> +static inline void cxl_enable_rcec(struct pci_dev *dev) { }
>>  static inline void cxl_rch_handle_error(struct pci_dev *dev,
>>  					struct aer_err_info *info) { }
>>  #endif
>> @@ -1494,7 +1504,7 @@ static int aer_probe(struct pcie_device *dev)
>>  		return status;
>>  	}
>>  
>> -	cxl_rch_enable_rcec(port);
>> +	cxl_enable_rcec(port);
>>  	aer_enable_rootport(rpc);
>>  	pci_info(port, "enabled with IRQ %d\n", dev->irq);
>>  	return 0;