[PATCH] drm/doc: Clarify the dumb object interfaces
Laurent Pinchart
laurent.pinchart at ideasonboard.com
Sun Jan 26 14:59:35 PST 2014
Hi Daniel,
Thank you for the patch.
On Friday 24 January 2014 17:58:40 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.
>
> v4: More text polish from Laurent's review.
>
> Cc: David Herrmann <dh.herrmann at gmail.com>
> Cc: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Acked-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
> Documentation/DocBook/drm.tmpl | 131 ++++++++++++++++++++------------------
> 1 file changed, 71 insertions(+), 60 deletions(-)
>
> diff --git a/Documentation/DocBook/drm.tmpl b/Documentation/DocBook/drm.tmpl
> index ed1d6d289022..67cfe184749c 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 @@ -968,9 +912,11 @@ int max_width, max_height;</synopsis>
> Frame buffers rely on the underneath memory manager for low-level
> memory operations. When creating a frame buffer applications pass a memory
> 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.
> + the <parameter>drm_mode_fb_cmd2</parameter> argument. For drivers using
> + GEM as their userspace buffer management interface this would be a GEM
> + handle. Drivers are however 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 handles.
> </para>
> <para>
> Drivers must first validate the requested frame buffer parameters
> passed @@ -992,7 +938,7 @@ int max_width, max_height;</synopsis>
> </para>
>
> <para>
> - The initailization of the new framebuffer instance is finalized with a
> + The initilization of the new framebuffer instance is finalized with a
> call to <function>drm_framebuffer_init</function> which takes a pointer
> to DRM frame buffer operations (struct
> <structname>drm_framebuffer_funcs</structname>). Note that this function
> @@ -1052,6 +998,71 @@ int max_width, max_height;</synopsis>
> <function>drm_framebuffer_unregister_private</function>.
> </sect2>
> <sect2>
> + <title>Dumb Buffer 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) 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 buffer objects.
> + </para>
> + </sect2>
> + <sect2>
> <title>Output Polling</title>
> <synopsis>void (*output_poll_changed)(struct drm_device
> *dev);</synopsis> <para>
--
Regards,
Laurent Pinchart
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