Re: [PATCH] drm/doc: Clarify the dumb object interfaces

Hi Daniel,

Thank you for the patch.

One last round of nitpicking (including a typo fix, which gives me an excuse for a couple more comments :-)).

On Thursday 23 January 2014 14:50:25 Daniel Vetter wrote:

• This is _not_ a generic interface to create gem objects, but just an interface to make early boot services (like boot splash) with a generic KMS userspace driver possible. Hence it's better to move the documentation for this from the GEM section to the KMS section, next to the creation of framebuffer objects.

• Make it really clear that the returned handle isn't necessarily a GEM object (it can also be e.g. a TTM handle when running on top of vmwgfx).

• Add a paragraph to make it clear that this is just for unaccelarated userspace - gpu drivers need to have their own buffer object creation ioctl which is hardware specific.

v2: Clarify that the documentation doesn't just apply to GEM-based drivers only but is now generally valid, as suggested by David.

v3: Polish the intro sentence a bit and one s/objects/handles/ for clarification, both suggested by Laurent.

Cc: David Herrmann dh.herrmann@gmail.com Cc: Laurent Pinchart laurent.pinchart@ideasonboard.com Signed-off-by: Daniel Vetter daniel.vetter@ffwll.ch

---

Documentation/DocBook/drm.tmpl | 129 ++++++++++++++++++++------------------ 1 file changed, 70 insertions(+), 59 deletions(-)

diff --git a/Documentation/DocBook/drm.tmpl b/Documentation/DocBook/drm.tmpl index ed1d6d289022..767318d5ddb6 100644 --- a/Documentation/DocBook/drm.tmpl +++ b/Documentation/DocBook/drm.tmpl

[snip]

@@ -1052,6 +998,71 @@ int max_width, max_height;</synopsis> <function>drm_framebuffer_unregister_private</function>. </sect2> <sect2>

•  <title>Dumb GEM Objects</title>
  

What about calling this "Dumb Memory Objects" (or something similar), as they're not specific to GEM ?

•  <para>
  

• The KMS API doesn't standardize backing storage object creation and
• leaves it to driver-specific ioctls. Furthermore actually creating a
• buffer object even for GEM-based drivers is done through a
• driver-specific ioctl - GEM only has a common userspace interface for
• sharing and destroying objects. While not an issue for full-fledged
• graphics stacks that include device-specific userspace components (in
• libdrm for instance), this limit makes DRM-based early boot graphics
• unnecessarily complex.

•  </para>
  

•  <para>
  

•    Dumb objects partly alleviate the problem by providing a standard
  

•    API to create dumb buffers suitable for scanout, which can then be
  

used

•    to create KMS frame buffers.
  

•  </para>
  

•  <para>
  

•    To support dumb objects drivers must implement the
  

•    <methodname>dumb_create</methodname>,
  

•    <methodname>dumb_destroy</methodname> and
  

•    <methodname>dumb_map_offset</methodname> operations.
  

•  </para>
  

•  <itemizedlist>
  

•    <listitem>
  

•      <synopsis>int (*dumb_create)(struct drm_file *file_priv, struct
  

drm_device *dev,

•               struct drm_mode_create_dumb *args);</synopsis>
  

•      <para>
  

•        The <methodname>dumb_create</methodname> operation creates a
  

driver

•    object (GEM or TTM handle) object suitable for scanout based on the
  

s/object suitable/suitable/ ?

•    width, height and depth from the struct
  

•    <structname>drm_mode_create_dumb</structname> argument. It fills the
  

•    argument's <structfield>handle</structfield>,
  

•    <structfield>pitch</structfield> and <structfield>size</structfield>
  

•    fields with a handle for the newly created object and its line
  

•        pitch and size in bytes.
  

•      </para>
  

•    </listitem>
  

•    <listitem>
  

•      <synopsis>int (*dumb_destroy)(struct drm_file *file_priv, struct
  

drm_device *dev,

•                uint32_t handle);</synopsis>
  

•      <para>
  

•        The <methodname>dumb_destroy</methodname> operation destroys a
  

dumb

•        object created by <methodname>dumb_create</methodname>.
  

•      </para>
  

•    </listitem>
  

•    <listitem>
  

•      <synopsis>int (*dumb_map_offset)(struct drm_file *file_priv,
  

struct drm_device *dev,

•                   uint32_t handle, uint64_t *offset);</synopsis>
  

•      <para>
  

•        The <methodname>dumb_map_offset</methodname> operation
  

associates an

•        mmap fake offset with the object given by the handle and
  

returns

•        it. Drivers must use the
  

•        <function>drm_gem_create_mmap_offset</function> function to
  

•        associate the fake offset as described in
  

•        <xref linkend="drm-gem-objects-mapping"/>.
  

•      </para>
  

•    </listitem>
  

•  </itemizedlist>
  

•  <para>
  

•    Note that dumb objects may not be used for gpu accelaration, as has
  

been

• attempted on some ARM embedded platforms. Such drivers really must have
• a hardware-specific ioctl to allocate suitable objects.

What about s/objects/memory objects/ ? "object" alone is rather vague for people not too familiar with DRM/KMS.

•  </para>
  

• </sect2>

• <sect2> <title>Output Polling</title> <synopsis>void (*output_poll_changed)(struct drm_device

*dev);</synopsis> <para>