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: <b104b695-a966-43e1-b4fa-1c8cce6d65e7@amd.com>
Date: Wed, 19 Nov 2025 16:02:40 -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 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

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'

Terry