Subject: Re: DRM_RAS (netlink genl family) for CPER Error logging?!

From: Rodrigo Vivi <[email-masked]>
Date: Thu, 30 Oct 2025 11:37:42 -0400

On Thu, Oct 30, 2025 at 10:47:18AM -0400, Rodrigo Vivi wrote:
> On Tue, Oct 28, 2025 at 03:13:15PM -0400, Rodrigo Vivi wrote:
> > On Mon, Sep 29, 2025 at 05:44:12PM -0400, Rodrigo Vivi wrote:
> > 
> > Hey Dave, Sima, AMD folks, Qualcomm folks,
> 
> + Netlink list and maintainers to get some feedback on the netlink usage
> proposed here.

The netdev mailing list blocked my bounces of the original discussions,
so for the overall context:

Usage of netlink as a drm-ras solution (with error counters in mind):
https://airlied.blogspot.com/2022/09/accelerators-bof-outcomes-summary.html

Proposal for error-counters with drm-ras generic netlink:
https://lore.kernel.org/dri-devel/[email-masked]/

Question about the error-logging RAS sub-case with CPER over this drm-ras netlink:
https://lore.kernel.org/dri-devel/[email-masked]/

> 
> Specially to check if there's any concern with CPER blob going through
> netlink or if there's any size limitation or concern.
> 
> > 
> > I have a key question to you below here.
> > 
> > > This work is a continuation of the great work started by Aravind ([1] and [2])
> > > in order to fulfill the RAS requirements and proposal as previously discussed
> > > and agreed in the Linux Plumbers accelerator's bof of 2022 [3].
> > > 
> > > [1]: https://lore.kernel.org/dri-devel/[email-masked]/
> > > [2]: https://lore.kernel.org/all/[email-masked]/
> > > [3]: https://airlied.blogspot.com/2022/09/accelerators-bof-outcomes-summary.html
> > > 
> > > During the past review round, Lukas pointed out that netlink had evolved
> > > in parallel during these years and that now, any new usage of netlink families
> > > would require the usage of the YAML description and scripts.
> > > 
> > > With this new requirement in place, the family name is hardcoded in the yaml file,
> > > so we are forced to have a single family name for the entire drm, and then we now
> > > we are forced to have a registration.
> > > 
> > > So, while doing the registration, we now created the concept of drm-ras-node.
> > > For now the only node type supported is the agreed error-counter. But that could
> > > be expanded for other cases like telemetry, requested by Zack for the qualcomm accel
> > > driver.
> > > 
> > > In this first version, only querying counter is supported. But also this is expandable
> > > to future introduction of multicast notification and also clearing the counters.
> > > 
> > > This design with multiple nodes per device is already flexible enough for driver
> > > to decide if it wants to handle error per device, or per IP block, or per error
> > > category. I believe this fully attend to the requested AMD feedback in the earlier
> > > reviews.
> > > 
> > > So, my proposal is to start simple with this case as is, and then iterate over
> > > with the drm-ras in tree so we evolve together according to various driver's RAS
> > > needs.
> > > 
> > > I have provided a documentation and the first Xe implementation of the counter
> > > as reference.
> > > 
> > > Also, it is worth to mention that we have a in-tree pyynl/cli.py tool that entirely
> > > exercises this new API, hence I hope this can be the reference code for the uAPI
> > > usage, while we continue with the plan of introducing IGT tests and tools for this
> > > and adjusting the internal vendor tools to open with open source developments and
> > > changing them to support these flows.
> > > 
> > > Example on MTL:
> > > 
> > > $ sudo ./tools/net/ynl/pyynl/cli.py \
> > >   --spec Documentation/netlink/specs/drm_ras.yaml \
> > >   --dump list-nodes
> > > [{'device-name': '00:02.0',
> > >   'node-id': 0,
> > >   'node-name': 'non-fatal',
> > >   'node-type': 'error-counter'},
> > >  {'device-name': '00:02.0',
> > >   'node-id': 1,
> > >   'node-name': 'correctable',
> > >   'node-type': 'error-counter'}]
> > 
> > As you can see on the drm-ras patch, we now have only a single family called
> > 'drm-ras', with that we have to register entry points, called 'nodes'
> > and for now only one type is existing: 'error-counter'
> > 
> > As I believe it was agreed in the Linux Plumbers accelerator's bof of 2022 [3].
> > 
> > Zack already indicated that for Qualcomm he doesn't need the error counters,
> > but another type, perhaps telemetry.
> > 
> > I need your feedback and input on yet another case here that goes side
> > by side with error-counters: Error logging.
> > 
> > One of the RAS requirements that we have is to emit CPER logs in certain
> > cases. AMD is currently using debugfs for printing the CPER entries that
> > accumulates in a ringbuffer. (iiuc).
> > 
> > Some folks are asking us to emit the CPER in the tracefs because
> > debugfs might not be available in some enterprise production images.
> > 
> > However, there's a concern on the tracefs usage for the error-logging case.
> > There is no active query path in the tracefs. If user needs to poll for
> > the latest CPER records it would need to pig-back on some other API
> > that would force the emit-trace(cper).
> > 
> > I believe that the cleanest way is to have another drm-ras node type
> > named 'error-logging' with a single operation that is query-logs,
> > that would be a dump of the available ring-buffer with latest known
> > cper records. Is this acceptable?
> > 
> > AMD folks, would you consider this to replace the current debugfs you
> > have?
> > 
> > Please let me know your thoughts.
> > 
> > We won't have an example for now, but it would be something like:
> > 
> > Thanks,
> > Rodrigo.
> > 
> > $ sudo ./tools/net/ynl/pyynl/cli.py \
> >   --spec Documentation/netlink/specs/drm_ras.yaml \
> >   --dump list-nodes
> > [{'device-name': '00:02.0',
> >   'node-id': 0,
> >   'node-name': 'non-fatal',
> >   'node-type': 'error-counter'},
> >  {'device-name': '00:02.0',
> >   'node-id': 1,
> >   'node-name': 'correctable',
> >   'node-type': 'error-counter'}
> >  'device-name': '00:02.0',
> >   'node-id': 2,
> >   'node-name': 'non-fatal',
> >   'node-type': 'error-logging'},
> >  {'device-name': '00:02.0',
> >   'node-id': 3,
> >   'node-name': 'correctable',
> >   'node-type': 'error-logging'}]
> > 
> > $ sudo ./tools/net/ynl/pyynl/cli.py \
> >    --spec Documentation/netlink/specs/drm_ras.yaml \
> >    --dump get-logs --json '{"node-id":3}'
> > [{'FRU': 'String with device info', 'CPER': !@#$#!@#$},
> > {'FRU': 'String with device info', 'CPER': !@#$#!@#$},
> > {'FRU': 'String with device info', 'CPER': !@#$#!@#$},
> > {'FRU': 'String with device info', 'CPER': !@#$#!@#$},
> > {'FRU': 'String with device info', 'CPER': !@#$#!@#$},
> > ]
> > 
> > Of course, details of the error-logging fields along with the CPER binary
> > is yet to be defined.
> > 
> > Oh, and the nodes names and split is device specific. The infra is flexible
> > enough. Driver can do whatever it makes sense for their device.
> > 
> > Any feedback or comment is really appreciated.
> > 
> > Thanks in advance,
> > Rodrigo.
> > 
> > > 
> > > $ sudo ./tools/net/ynl/pyynl/cli.py \
> > >   --spec Documentation/netlink/specs/drm_ras.yaml \
> > >   --dump get-error-counters --json '{"node-id":1}'
> > > [{'error-id': 0, 'error-name': 'GT Error', 'error-value': 0},
> > >  {'error-id': 4, 'error-name': 'Display Error', 'error-value': 0},
> > >  {'error-id': 8, 'error-name': 'GSC Error', 'error-value': 0},
> > >  {'error-id': 12, 'error-name': 'SG Unit Error', 'error-value': 0},
> > >  {'error-id': 16, 'error-name': 'SoC Error', 'error-value': 0},
> > >  {'error-id': 17, 'error-name': 'CSC Error', 'error-value': 0}]
> > > 
> > > $ sudo ./tools/net/ynl/pyynl/cli.py \
> > >   --spec Documentation/netlink/specs/drm_ras.yaml \
> > >   --do query-error-counter --json '{"node-id": 0, "error-id": 12}'
> > > {'error-id': 12, 'error-name': 'SG Unit Error', 'error-value': 0}
> > > 
> > > $ sudo ./tools/net/ynl/pyynl/cli.py \
> > >   --spec Documentation/netlink/specs/drm_ras.yaml \
> > >   --do query-error-counter --json '{"node-id": 1, "error-id": 16}'
> > > {'error-id': 16, 'error-name': 'SoC Error', 'error-value': 0}
> > > 
> > > Thanks,
> > > Rodrigo.
> > > 
> > > Cc: Hawking Zhang <[email-masked]>
> > > Cc: Alex Deucher <[email-masked]>
> > > Cc: Zack McKevitt <[email-masked]>
> > > Cc: Lukas Wunner <[email-masked]>
> > > Cc: Dave Airlie <[email-masked]>
> > > Cc: Simona Vetter <[email-masked]>
> > > Cc: Aravind Iddamsetty <[email-masked]>
> > > Cc: Joonas Lahtinen <[email-masked]>
> > > Signed-off-by: Rodrigo Vivi <[email-masked]>
> > > 
> > > Rodrigo Vivi (2):
> > >   drm/ras: Introduce the DRM RAS infrastructure over generic netlink
> > >   drm/xe: Introduce the usage of drm_ras with supported HW errors
> > > 
> > >  Documentation/gpu/drm-ras.rst              | 109 +++++++
> > >  Documentation/netlink/specs/drm_ras.yaml   | 130 ++++++++
> > >  drivers/gpu/drm/Kconfig                    |   9 +
> > >  drivers/gpu/drm/Makefile                   |   1 +
> > >  drivers/gpu/drm/drm_drv.c                  |   6 +
> > >  drivers/gpu/drm/drm_ras.c                  | 357 +++++++++++++++++++++
> > >  drivers/gpu/drm/drm_ras_genl_family.c      |  42 +++
> > >  drivers/gpu/drm/drm_ras_nl.c               |  54 ++++
> > >  drivers/gpu/drm/xe/regs/xe_hw_error_regs.h |  22 ++
> > >  drivers/gpu/drm/xe/xe_hw_error.c           | 155 ++++++++-
> > >  include/drm/drm_ras.h                      |  76 +++++
> > >  include/drm/drm_ras_genl_family.h          |  17 +
> > >  include/drm/drm_ras_nl.h                   |  24 ++
> > >  include/uapi/drm/drm_ras.h                 |  49 +++
> > >  14 files changed, 1049 insertions(+), 2 deletions(-)
> > >  create mode 100644 Documentation/gpu/drm-ras.rst
> > >  create mode 100644 Documentation/netlink/specs/drm_ras.yaml
> > >  create mode 100644 drivers/gpu/drm/drm_ras.c
> > >  create mode 100644 drivers/gpu/drm/drm_ras_genl_family.c
> > >  create mode 100644 drivers/gpu/drm/drm_ras_nl.c
> > >  create mode 100644 include/drm/drm_ras.h
> > >  create mode 100644 include/drm/drm_ras_genl_family.h
> > >  create mode 100644 include/drm/drm_ras_nl.h
> > >  create mode 100644 include/uapi/drm/drm_ras.h
> > > 
> > > -- 
> > > 2.51.0
> > >