Re: [PATCH 01/19] drm/doc: Clarify the dumb object interfaces

Hi

On Thu, Jan 23, 2014 at 9:52 AM, Daniel Vetter daniel.vetter@ffwll.ch 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.

Cc: Laurent Pinchart laurent.pinchart@ideasonboard.com> Signed-off-by: Daniel Vetter daniel.vetter@ffwll.ch

---

Documentation/DocBook/drm.tmpl | 125 ++++++++++++++++++++++------------------- 1 file changed, 68 insertions(+), 57 deletions(-)

diff --git a/Documentation/DocBook/drm.tmpl b/Documentation/DocBook/drm.tmpl index ed1d6d289022..9c3fdd59c995 100644 --- a/Documentation/DocBook/drm.tmpl +++ b/Documentation/DocBook/drm.tmpl @@ -830,62 +830,6 @@ char *date;</synopsis> </para> </sect3> <sect3>

•    <title>Dumb GEM Objects</title>
  

•    <para>
  

•      The GEM API doesn't standardize GEM objects creation and leaves it to
  

•      driver-specific ioctls. 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 GEM 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 GEM 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 GEM
  

•          object suitable for scanout based on the 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 GEM 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
  

•          GEM 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 GEM 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>
  

•  </sect3>
  

•  <sect3>
     <title>Memory Coherency</title>
     <para>
       When mapped to the device or used in a command buffer, backing pages
  

@@ -970,7 +914,9 @@ int max_width, max_height;</synopsis> handle (or a list of memory handles for multi-planar formats) through the <parameter>drm_mode_fb_cmd2</parameter> argument. This document assumes that the driver uses GEM, those handles thus reference GEM

•    objects.
  

•    objects. But drivers are free to use their own backing storage object
  

•   handles, e.g. vmwgfx directly exposes special TTM handles to userspace
  

•   and so expects TTM handles in the create ioctl and not GEM objects.
  

Maybe remove the sentence saying "this document assumes that the driver uses GEM". I don't see where we explicitly do that. Otherwise the patch looks fine.

Thanks David

   </para>
   <para>
     Drivers must first validate the requested frame buffer parameters passed

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

•  <title>Dumb GEM Objects</title>
  

•  <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
  

•       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.
  

•  </para>
  

• </sect2>

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

-- 1.8.5.2

---

dri-devel mailing list dri-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/dri-devel