Re: [PATCH 4/9] drm/xe: Add a new debug focused configfs group

[Gustavo Sousa <gustavo.sousa@intel.com>]

"Summers, Stuart" <stuart.summers@intel.com> writes:

> On Mon, 2026-05-04 at 14:28 -0300, Gustavo Sousa wrote:
>> "Summers, Stuart" <stuart.summers@intel.com> writes:
>> 
>> > On Mon, 2026-05-04 at 12:42 -0300, Gustavo Sousa wrote:
>> > > Stuart Summers <stuart.summers@intel.com> writes:
>> > > 
>> > > > Add the skeleton code for a new debug specific configfs group.
>> > > > 
>> > > > Signed-off-by: Stuart Summers <stuart.summers@intel.com>
>> > > > Assisted-by: Copilot:claude-opus-4.7
>> > > > ---
>> > > >  drivers/gpu/drm/xe/Makefile            |  2 ++
>> > > >  drivers/gpu/drm/xe/xe_configfs.c       |  4 ++++
>> > > >  drivers/gpu/drm/xe/xe_configfs_debug.c | 14 ++++++++++++++
>> > > >  drivers/gpu/drm/xe/xe_configfs_debug.h |  8 ++++++++
>> > > >  drivers/gpu/drm/xe/xe_configfs_types.h |  7 +++++++
>> > > >  5 files changed, 35 insertions(+)
>> > > >  create mode 100644 drivers/gpu/drm/xe/xe_configfs_debug.c
>> > > >  create mode 100644 drivers/gpu/drm/xe/xe_configfs_debug.h
>> > > > 
>> > > > diff --git a/drivers/gpu/drm/xe/Makefile
>> > > > b/drivers/gpu/drm/xe/Makefile
>> > > > index 09661f079d03..b58667b0b18e 100644
>> > > > --- a/drivers/gpu/drm/xe/Makefile
>> > > > +++ b/drivers/gpu/drm/xe/Makefile
>> > > > @@ -161,6 +161,8 @@ xe-$(CONFIG_HWMON) += xe_hwmon.o
>> > > >  
>> > > >  xe-$(CONFIG_PERF_EVENTS) += xe_pmu.o
>> > > >  xe-$(CONFIG_CONFIGFS_FS) += xe_configfs.o
>> > > > +xe_debug_configfs_obj-$(CONFIG_DRM_XE_DEBUG) :=
>> > > > xe_configfs_debug.o
>> > > > +xe-$(CONFIG_CONFIGFS_FS) += $(xe_debug_configfs_obj-y)
>> > > 
>> > > What are the downsides of keeping this available for non-debug
>> > > builds?
>> > > 
>> > > I imagine that the debug configfs could be useful for someone not
>> > > involved in kernel development working together with the
>> > > developers
>> > > to
>> > > debug issues without needing to rebuild their kernel.
>> > 
>> > So the focal parameter we had in i915 was enable_rc6. Something
>> > like
>> > this is what we explicitly don't want to expose to a general user
>> > as it
>> > can have unforeseen consequences (like having very high power
>> > usage).
>> > But, having the ability to disable rc6 for debug purposes as a
>> > developer is extremely useful at narrowing down certain types of
>> > bugs
>> > at the hardware/software interface.
>> 
>> We could probably keep the debug stuff available but cause a taint if
>> they ever get used?
>
> So the tainting is really just for our CI I think. This won't
> necessarily impact end users - at least on the client side - who might
> just ignore it (or not even notice it).

I *think* tainting is not only for CI (someone could correct me here).
I see that our driver adds a taint when the user is applying some
parameters (module parameters or configfs) that alters the "officially
supported" behavior of the driver.

Some examples I could find are usages of module_param_named_unsafe() in
the module param front, and setup_configfs_post_ctx_restore_bb(),
setup_configfs_mid_ctx_restore_bb() in configfs.

>
>> 
>> The scenario I had in mind is someone who is not familiar with
>> building
>> their own kernel working together with the development community on a
>> hard-to-reproduce issue and some of the debug configfs attributes
>> being
>> useful to gather more relevant data.
>
> Yeah but IMO we really should be able to instruct such a user how to do
> that - the steps there aren't too difficult if they're already
> installing kernels etc.
>
> A lot of our debug hooks are already held under various Kconfig options
> anyway like DRM_XE_DEBUG, DRM_XE_DEBUG_GUC, DRM_XE_DEBUG_VM, etc. And a
> lot of the information under those Kconfigs are also critical for
> different debugs.

Are those due to performance or resource usage implications if they are
kept enabled?  If so, is this the same case here?

>
> I'd really prefer to keep these under DRM_XE_DEBUG (or some other
> Kconfig) if possible so we can maximize the ease of adding new
> parameters as specific debugs come up.

But why would keeping them under a build flag make it easier to add new
parameters as opposed to always keeping the knobs available for use?

--
Gustavo Sousa

>
> Thanks,
> Stuart
>
>> 
>> --
>> Gustavo Sousa
>> 
>> > 
>> > That's just one example, but there are a bunch of things that could
>> > fit
>> > this category and I expect we'll have even more use cases over
>> > time. 
>> > 
>> > Right now we have to hold these types of changes in a side branch
>> > not
>> > exposed externally and I really want to converge our processes so
>> > we
>> > can more easily make these kinds of changes and let us debug
>> > directly
>> > out of drm-tip.
>> > 
>> > > 
>> > > >  
>> > > >  # graphics virtualization (SR-IOV) support
>> > > >  xe-y += \
>> > > > diff --git a/drivers/gpu/drm/xe/xe_configfs.c
>> > > > b/drivers/gpu/drm/xe/xe_configfs.c
>> > > > index 12b7fe65446d..85df8ce5cf2a 100644
>> > > > --- a/drivers/gpu/drm/xe/xe_configfs.c
>> > > > +++ b/drivers/gpu/drm/xe/xe_configfs.c
>> > > > @@ -1006,6 +1006,10 @@ static struct config_group
>> > > > *xe_config_make_device_group(struct config_group *gro
>> > > >                 config_group_init_type_name(&dev->sriov,
>> > > > "sriov",
>> > > > &xe_config_sriov_type);
>> > > >                 configfs_add_default_group(&dev->sriov, &dev-
>> > > > > group);
>> > > >         }
>> > > > +#if IS_ENABLED(CONFIG_DRM_XE_DEBUG)
>> > > > +       config_group_init_type_name(&dev->debug, "debug",
>> > > > &xe_configfs_debug_type);
>> > > > +       configfs_add_default_group(&dev->debug, &dev->group);
>> > > > +#endif
>> > > 
>> > > I guess there isn't much we can do about it today, but, based on
>> > > what
>> > > I
>> > > read in configfs documentation a while ago, I suspect it wasn't
>> > > really
>> > > designed with arbitrary hierarchies of config items in mind.  It
>> > > would
>> > > be nice if there was an API for that though.
>> > > 
>> > > Basically, a config group is expected to be a directory to
>> > > contain a
>> > > set
>> > > of config items of the same type, which is not the case on our
>> > > current
>> > > usage (i.e. the "sriov" and now the "debug" group).
>> > > 
>> > > I guess we are able to get our desired behavior (basically just a
>> > > subdirectory behaving as a config item) by not implementing the
>> > > "make_item" hook.  Not sure if that's an expected use of the API
>> > > or
>> > > if
>> > > that's more of a hack on our side and could come back to bite us
>> > > in
>> > > the
>> > > future.
>> > 
>> > Hm.. ok that's good feedback. I do like bucketing these in groups
>> > and
>> > subdirectories. It also makes it easy to show or not show based on
>> > the
>> > Kconfig. But let me go through and make sure there isn't something
>> > more
>> > suited here. Happy to hear any other feedback as well here.
>> > 
>> > Thanks,
>> > Stuart
>> > 
>> > > 
>> > > --
>> > > Gustavo Sousa
>> > > 
>> > > >  
>> > > >         mutex_init(&dev->lock);
>> > > >  
>> > > > diff --git a/drivers/gpu/drm/xe/xe_configfs_debug.c
>> > > > b/drivers/gpu/drm/xe/xe_configfs_debug.c
>> > > > new file mode 100644
>> > > > index 000000000000..45617282cec5
>> > > > --- /dev/null
>> > > > +++ b/drivers/gpu/drm/xe/xe_configfs_debug.c
>> > > > @@ -0,0 +1,14 @@
>> > > > +// SPDX-License-Identifier: MIT
>> > > > +/*
>> > > > + * Copyright © 2026 Intel Corporation
>> > > > + */
>> > > > +
>> > > > +#include <linux/configfs.h>
>> > > > +#include <linux/module.h>
>> > > > +
>> > > > +#include "xe_configfs_debug.h"
>> > > > +#include "xe_configfs_types.h"
>> > > > +
>> > > > +const struct config_item_type xe_configfs_debug_type = {
>> > > > +       .ct_owner       = THIS_MODULE,
>> > > > +};
>> > > > diff --git a/drivers/gpu/drm/xe/xe_configfs_debug.h
>> > > > b/drivers/gpu/drm/xe/xe_configfs_debug.h
>> > > > new file mode 100644
>> > > > index 000000000000..01170dc2f97e
>> > > > --- /dev/null
>> > > > +++ b/drivers/gpu/drm/xe/xe_configfs_debug.h
>> > > > @@ -0,0 +1,8 @@
>> > > > +/* SPDX-License-Identifier: MIT */
>> > > > +/*
>> > > > + * Copyright © 2026 Intel Corporation
>> > > > + */
>> > > > +#ifndef _XE_CONFIGFS_DEBUG_H_
>> > > > +#define _XE_CONFIGFS_DEBUG_H_
>> > > > +
>> > > > +#endif /* _XE_CONFIGFS_DEBUG_H_ */
>> > > > diff --git a/drivers/gpu/drm/xe/xe_configfs_types.h
>> > > > b/drivers/gpu/drm/xe/xe_configfs_types.h
>> > > > index 935097aafa96..c9d94a3c26a7 100644
>> > > > --- a/drivers/gpu/drm/xe/xe_configfs_types.h
>> > > > +++ b/drivers/gpu/drm/xe/xe_configfs_types.h
>> > > > @@ -24,6 +24,9 @@ struct wa_bb {
>> > > >  struct xe_config_group_device {
>> > > >         struct config_group group;
>> > > >         struct config_group sriov;
>> > > > +#if IS_ENABLED(CONFIG_DRM_XE_DEBUG)
>> > > > +       struct config_group debug;
>> > > > +#endif
>> > > >  
>> > > >         struct xe_config_device {
>> > > >                 struct wa_bb
>> > > > ctx_restore_mid_bb[XE_ENGINE_CLASS_MAX];
>> > > > @@ -56,4 +59,8 @@ static inline struct xe_config_device
>> > > > *xe_configfs_to_device(struct config_item
>> > > >         return &xe_configfs_to_group_device(item)->config;
>> > > >  }
>> > > >  
>> > > > +#if IS_ENABLED(CONFIG_DRM_XE_DEBUG)
>> > > > +extern const struct config_item_type xe_configfs_debug_type;
>> > > > +#endif
>> > > > +
>> > > >  #endif /* _XE_CONFIGFS_TYPES_H_ */
>> > > > -- 
>> > > > 2.43.0