Re: [Intel-gfx] [PATCH v5 4/7] drm/i915/gt: create per-tile sysfs interface

Andi Shyti
2022-03-13T19:45:38Z

Hi Andrzej,

I'm sorry, but I'm not fully understanding,

> > > > +struct intel_gt *intel_gt_sysfs_get_drvdata(struct device *dev,
> > > > + const char *name)
> > > > +{
> > > > + struct kobject *kobj = &dev->kobj;
> > > > +
> > > > + /*
> > > > + * We are interested at knowing from where the interface
> > > > + * has been called, whether it's called from gt/ or from
> > > > + * the parent directory.
> > > > + * From the interface position it depends also the value of
> > > > + * the private data.
> > > > + * If the interface is called from gt/ then private data is
> > > > + * of the "struct intel_gt *" type, otherwise it's * a
> > > > + * "struct drm_i915_private *" type.
> > > > + */
> > > > + if (!is_object_gt(kobj)) {
> > > > + struct drm_i915_private *i915 = kdev_minor_to_i915(dev);
> > > > +
> > > > + pr_devel_ratelimited(DEPRECATED
> > > > + "%s (pid %d) is accessing deprecated %s "
> > > > + "sysfs control, please use gt/gt<n>/%s instead\n",
> > > > + current->comm, task_pid_nr(current), name, name);
> > > > + return to_gt(i915);
> > > > + }
> > > > +
> > > > + return kobj_to_gt(kobj);
> > > It took some time for me to understand what is going on here.
> > > We have dev argument which sometimes can point to "struct device", sometimes
> > > to "struct kobj_gt", but it's type suggests differently, quite ugly.
> > > I wonder if wouldn't be better to use __ATTR instead of DEVICE_ATTR* as in
> > > case of intel_engines_add_sysfs. This way abstractions would look better,
> > > hopefully.
> > How would it help?
> >
> > The difference is that I'm adding twice different interfaces with
> > the same name and different location (i.e. different object). The
> > legacy intrefaces inherit the object from drm and I'm preserving
> > that reference.
> >
> > While the new objects would derive from the previous and they are
> > pretty much like intel_engines_add_sysfs().
>
> I was not clear on the issue. Here in case of 'id' attribute it is defined
> as device_attribute, but in kobj_type.sysfs_ops you assign formally
> incompatible &kobj_sysfs_ops.

'kobj_sysfs_ops' is of the type 'kobj_type'.

> kobj_sysfs_ops expects kobj_attribute! Fortunately kobj_attribute is 'binary
> compatible' with device_attribute and kobj is at beginning of struct device
> as well, so it does not blow up, but I wouldn't say it is clean solution :)
> If you look at intel_engines_add_sysfs you can see that all attributes are
> defined as kobj_attribute.

That's exactly the approach I use in the next patches for the
power management files, I use "struct kobj_gt" wrapped around
"struct kobject". But I'm using that only for the GT files.

Are you, btw, suggesting to use this same approache also for the
legacy files that for now have a pointer to the drm kobject? This
way I would need to add more information, like the pointer to
i915 and gt_id. This way I wouldn't need the files above that
look hacky to you. Is this what you mean?

Andi