Re: [PATCH v2 2/3] drm: Add a drm_gem_objects_lookup helper

From: Rob Herring <robh@kernel.org>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: Sean Paul <sean@poorly.run>, Lyude Paul <lyude@redhat.com>,
	Eric Anholt <eric@anholt.net>,
	Maxime Ripard <maxime.ripard@bootlin.com>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Joerg Roedel <joro@8bytes.org>,
	Neil Armstrong <narmstrong@baylibre.com>,
	Will Deacon <will.deacon@arm.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	David Airlie <airlied@linux.ie>,
	"list@263.net:IOMMU DRIVERS <iommu@lists.linux-foundation.org>,
	Joerg Roedel <joro@8bytes.org>,
	" <iommu@lists.linux-foundation.org>,
	Alyssa Rosenzweig <alyssa@rosenzweig.io>,
	Robin Murphy <robin.murphy@arm.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2 2/3] drm: Add a drm_gem_objects_lookup helper
Date: Mon, 1 Apr 2019 11:59:15 -0500	[thread overview]
Message-ID: <CAL_JsqJ4uppXc_Sti67z0ZBJ4sw1RPgNHCg6usqpUmbQcGQmpQ@mail.gmail.com> (raw)
In-Reply-To: <CAKMK7uE7-XV3cZxS8GT_EDa7yojOLPQi+LqkF85h_0z_JL6gYw@mail.gmail.com>

On Mon, Apr 1, 2019 at 8:07 AM Daniel Vetter <daniel@ffwll.ch> wrote:
>
> On Mon, Apr 1, 2019 at 9:47 AM Rob Herring <robh@kernel.org> wrote:
> >
> > Similar to the single handle drm_gem_object_lookup(),
> > drm_gem_objects_lookup() takes an array of handles and returns an array
> > of GEM objects.
> >
> > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > Cc: Maxime Ripard <maxime.ripard@bootlin.com>
> > Cc: Sean Paul <sean@poorly.run>
> > Cc: David Airlie <airlied@linux.ie>
> > Cc: Daniel Vetter <daniel@ffwll.ch>
> > Signed-off-by: Rob Herring <robh@kernel.org>
> > ---
> >  drivers/gpu/drm/drm_gem.c | 46 +++++++++++++++++++++++++++++++--------
> >  include/drm/drm_gem.h     |  2 ++
> >  2 files changed, 39 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> > index 388b3742e562..5c9bff45e5e1 100644
> > --- a/drivers/gpu/drm/drm_gem.c
> > +++ b/drivers/gpu/drm/drm_gem.c
> > @@ -663,6 +663,42 @@ void drm_gem_put_pages(struct drm_gem_object *obj, struct page **pages,
> >  }
> >  EXPORT_SYMBOL(drm_gem_put_pages);
> >
> > +/**
> > + * drm_gem_objects_lookup - look up GEM objects from an array of handles
> > + * @filp: DRM file private date
> > + * @handle: pointer to array of userspace handle
> > + * @count: size of handle array
> > + * @objs: pointer to array of drm_gem_object pointers
> > + *
> > + * Returns:
> > + *
> > + * @objs filled in with GEM object pointers. -ENOENT is returned on a lookup
> > + * failure. 0 is returned on success.
>
> Bonus points for adding references between the array and normal lookup
> functions to guide people around. Also a comment that the buffers need
> to be released with drm_gem_object_put().
>
> > + */
> > +int drm_gem_objects_lookup(struct drm_file *filp, u32 *handle, int count,
> > +                          struct drm_gem_object **objs)
>
> With a pointer to a pointer I'd expect this function to do the
> allocation, but it doesn't. Normal pointer is enough to pass an array.
> Also maybe make the handle pointer
> const, so it's clear that it's an input parameter.

I thought about doing the allocation here, but then I couldn't
implement the single drm_gem_object_lookup() using this function.
Maybe I can refactor in 3 functions making this one a static function.

Rob

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