Re: [PATCH 6/9] drm/{i915,xe}/fbdev: add intel_fbdev_fb_bo_destroy()

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Sep 17, 2025 at 03:33:31PM +0300, Jani Nikula wrote:
> On Thu, 04 Sep 2025, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> > On Wed, Sep 03, 2025 at 11:32:03PM +0300, Jani Nikula wrote:
> >> xe does xe_bo_unpin_map_no_vm() on the failure path. Add a common helper
> >> to enable further refactoring.
> >> 
> >> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> >> ---
> >>  drivers/gpu/drm/i915/display/intel_fbdev_fb.c | 5 +++++
> >>  drivers/gpu/drm/i915/display/intel_fbdev_fb.h | 1 +
> >>  drivers/gpu/drm/xe/display/intel_fbdev_fb.c   | 7 ++++++-
> >>  3 files changed, 12 insertions(+), 1 deletion(-)
> >> 
> >> diff --git a/drivers/gpu/drm/i915/display/intel_fbdev_fb.c b/drivers/gpu/drm/i915/display/intel_fbdev_fb.c
> >> index 3837973b0d25..6b70823ce5ef 100644
> >> --- a/drivers/gpu/drm/i915/display/intel_fbdev_fb.c
> >> +++ b/drivers/gpu/drm/i915/display/intel_fbdev_fb.c
> >> @@ -51,6 +51,11 @@ struct drm_gem_object *intel_fbdev_fb_bo_create(struct drm_device *drm, int size
> >>  	return &obj->base;
> >>  }
> >>  
> >> +void intel_fbdev_fb_bo_destroy(struct drm_gem_object *obj)
> >> +{
> >> +	/* nop? */
> >
> > gem_object_put() is what destroys the bo on i915, so I think you're
> > introducing a leak in the next patch with this nop implementation.
> >
> > xe seems to be riddled with footguns here since it conflates
> > creation+pinning+whatever in the same thing (and I guess it
> > doesn't know how to clean all that up when the last reference
> > to the object disappears?) and you have to use that horribly
> > misnamed function instead...
> 
> Hmm, can we just slap i915_gem_object_put(obj) in there?

That would at least match how it behaves currently. Though I
didn't look too deeply whether that is 100% sufficient to clean
up properly.

> 
> The i915 variant of intel_fbdev_fb_alloc() ignores errors from
> intel_framebuffer_create() and just unconditionally does
> i915_gem_object_put() afterwards:
> 
> 	fb = intel_framebuffer_create(intel_bo_to_drm_bo(obj),
> 				      drm_get_format_info(display->drm,
> 							  mode_cmd.pixel_format,
> 							  mode_cmd.modifier[0]),
> 				      &mode_cmd);
> 	i915_gem_object_put(obj);
> 
> 	return to_intel_framebuffer(fb);
> 
> Presumably the refcounts are handled correctly either way.
> 
> It's just a bit fishy that the potential error pointer from
> intel_framebuffer_create() goes through to_intel_framebuffer() to the
> caller.

Yeah, would be less confusing to just check for the error
explicitly.

-- 
Ville Syrjälä
Intel