linux-kernel - Re: [RESEND v13 12/25] cxl/pci: Unify CXL trace logging for CXL Endpoints and CXL Ports

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Message-ID: <c5adb070-a45d-43e2-8d9c-515f5cefe6aa@amd.com>
Date: Fri, 21 Nov 2025 08:56:03 -0600
From: "Bowman, Terry" <terry.bowman@....com>
To: dan.j.williams@...el.com, dave@...olabs.net, jonathan.cameron@...wei.com,
 dave.jiang@...el.com, alison.schofield@...el.com, bhelgaas@...gle.com,
 shiju.jose@...wei.com, ming.li@...omail.com,
 Smita.KoralahalliChannabasappa@....com, rrichter@....com,
 dan.carpenter@...aro.org, PradeepVineshReddy.Kodamati@....com,
 lukas@...ner.de, Benjamin.Cheatham@....com,
 sathyanarayanan.kuppuswamy@...ux.intel.com, linux-cxl@...r.kernel.org,
 alucerop@....com, ira.weiny@...el.com
Cc: linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [RESEND v13 12/25] cxl/pci: Unify CXL trace logging for CXL
 Endpoints and CXL Ports



On 11/19/2025 5:40 PM, dan.j.williams@...el.com wrote:
> Bowman, Terry wrote:
>>
>> On 11/19/2025 3:23 PM, dan.j.williams@...el.com wrote:
>>> Terry Bowman wrote:
>>>> CXL currently has separate trace routines for CXL Port errors and CXL
>>>> Endpoint errors. This is inconvenient for the user because they must enable
>>>> 2 sets of trace routines. Make updates to the trace logging such that a
>>>> single trace routine logs both CXL Endpoint and CXL Port protocol errors.
>>> No, this is not inconvient, this is required for compatible evolution of
>>> tracepoints. The change in this patch breaks compatibility as it
>>> violates the expectation the type and order of TP_ARGS does not change
>>> from one kernel to next.
>>>
>>>> Keep the trace log fields 'memdev' and 'host'. While these are not accurate
>>>> for non-Endpoints the fields will remain as-is to prevent breaking
>>>> userspace RAS trace consumers.
>>>>
>>>> Add serial number parameter to the trace logging. This is used for EPs
>>>> and 0 is provided for CXL port devices without a serial number.
>>>>
>>>> Leave the correctable and uncorrectable trace routines' TP_STRUCT__entry()
>>>> unchanged with respect to member data types and order.
>>>>
>>>> Below is output of correctable and uncorrectable protocol error logging.
>>>> CXL Root Port and CXL Endpoint examples are included below.
>>>>
>>>> Root Port:
>>>> cxl_aer_correctable_error: memdev=0000:0c:00.0 host=pci0000:0c serial: 0 status='CRC Threshold Hit'
>>>> cxl_aer_uncorrectable_error: memdev=0000:0c:00.0 host=pci0000:0c serial: 0 status: 'Cache Byte Enable Parity Error' first_error: 'Cache Byte Enable Parity Error'
>>> A root port is not a "memdev", another awkward side effect of trying to
>>> combine 2 trace points with different use cases.
>>>
>>> So a NAK from me for this change (unless there is an strong reason for
>>> Linux to inflict the compat breakage), please keep the separate
>>> tracepoints they are for distinctly different use cases. A memdev
>>> protocol error is contained to that memdev, a port protocol error
>>> implicates every CXL.cachemem descendant of that port.
>> I misunderstood this comment from previous code review:
>> https://lore.kernel.org/linux-cxl/67aea897cfe55_2d1e294ca@dwillia2-xfh.jf.intel.com.notmuch/#t
> No, you did not misunderstand, I just did not realize at the time I was
> asking for compatibility breakage with that suggestion. Apologies for
> that thrash.
>
>> Are you OK with the following format for Port devices? Or let me know what format is needed.
>> cxl_port_aer_correctable_error: device=port1 parent=root0 status='Received Error From Physical Layer'
>> cxl_port_aer_uncorrectable_error: device=port1 parent=root0 status: 'Memory Byte Enable Parity Error' first_error: 'Memory Byte Enable Parity Erro'
> That looks good to me.
>
> Also, I realize this patch set has gone through many revisions. We
> really need to get at least some of these pre-req patches into a topic
> branch so they do not need to keep being sent out in this large series.


Do we want a serial number field in the port log (missing above)? CXL USP and DSP will have serial 
from the Identify Command. It would make the port logs look like:

cxl_port_aer_correctable_error: device=port1 parent=root0 serial=0 status='Received Error From Physical Layer'
cxl_port_aer_uncorrectable_error: device=port1 parent=root0 serial=0 status: 'Memory Byte Enable Parity Error' first_error: 'Memory Byte 

-Terry