Re: [PATCH 2/3] drm/doc: Drop chapter "KMS Initialization and Cleanup"

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On Wed, Jan 30, 2019 at 09:04:23PM +0000, Kazlauskas, Nicholas wrote:
> On 1/30/19 4:02 PM, Daniel Vetter wrote:
> > On Wed, Jan 30, 2019 at 05:33:00PM +0000, Kazlauskas, Nicholas wrote:
> >> On 1/30/19 11:30 AM, Daniel Vetter wrote:
> >>> It only talks about crtc, brings up intel as an exampel and I think is
> >>
> >> nit: Should be "example".
> > 
> > Will fix when applying.
> > 
> >>> more misleading than useful really. Plus we have lots of discussion
> >>> about how your standard kms driver should be initialized/cleaned up,
> >>> so maybe better to document this when we have a better idea.
> >>>
> >>> Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> >>> ---
> >>>    Documentation/gpu/drm-kms.rst | 96 -----------------------------------
> >>>    1 file changed, 96 deletions(-)
> >>>
> >>> diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst
> >>> index 75c882e09fee..23a3c986ef6d 100644
> >>> --- a/Documentation/gpu/drm-kms.rst
> >>> +++ b/Documentation/gpu/drm-kms.rst
> >>> @@ -410,102 +410,6 @@ Encoder Functions Reference
> >>>    .. kernel-doc:: drivers/gpu/drm/drm_encoder.c
> >>>       :export:
> >>>    
> >>> -KMS Initialization and Cleanup
> >>> -==============================
> >>> -
> >>> -A KMS device is abstracted and exposed as a set of planes, CRTCs,
> >>> -encoders and connectors. KMS drivers must thus create and initialize all
> >>> -those objects at load time after initializing mode setting.
> >>> -
> >>> -CRTCs (:c:type:`struct drm_crtc <drm_crtc>`)
> >>> ---------------------------------------------
> >>> -
> >>> -A CRTC is an abstraction representing a part of the chip that contains a
> >>> -pointer to a scanout buffer. Therefore, the number of CRTCs available
> >>> -determines how many independent scanout buffers can be active at any
> >>> -given time. The CRTC structure contains several fields to support this:
> >>> -a pointer to some video memory (abstracted as a frame buffer object), a
> >>> -display mode, and an (x, y) offset into the video memory to support
> >>> -panning or configurations where one piece of video memory spans multiple
> >>> -CRTCs.
> >>
> >> This is mostly a duplicate of what's already in the CRTC abstraction
> >> section but it may be worth carrying over the bit about  "the number of
> >> CRTCs available determining the number of independent scanout buffers
> >> that can be active at any given time".
> > 
> > Oh I didn't even read this. This is just plain wrong and probably predates
> > drm_plane (when it kinda was true-ish, if you'd ignore cursors). Now this
> > would map to number of drm_planes, except
> > - cursors can still be an exceptions
> > - yuv multi-planar might or might not be multiple planes per drm_plane.
> > 
> > Aka it's really complicated :-)
> > 
> > This is definitely much better explained in the kms overview section at
> > the top of:
> > 
> > https://dri.freedesktop.org/docs/drm/gpu/drm-kms.html#overview
> > 
> > Plus everything that's getting linked from there ofc.
> > 
> >>> -
> >>> -CRTC Initialization
> >>> -~~~~~~~~~~~~~~~~~~~
> >>> -
> >>> -A KMS device must create and register at least one struct
> >>> -:c:type:`struct drm_crtc <drm_crtc>` instance. The instance is
> >>> -allocated and zeroed by the driver, possibly as part of a larger
> >>> -structure, and registered with a call to :c:func:`drm_crtc_init()`
> >>> -with a pointer to CRTC functions.
> >>> -
> >>> -
> >>> -Cleanup
> >>> --------
> >>> -
> >>> -The DRM core manages its objects' lifetime. When an object is not needed
> >>> -anymore the core calls its destroy function, which must clean up and
> >>> -free every resource allocated for the object. Every
> >>> -:c:func:`drm_\*_init()` call must be matched with a corresponding
> >>> -:c:func:`drm_\*_cleanup()` call to cleanup CRTCs
> >>> -(:c:func:`drm_crtc_cleanup()`), planes
> >>> -(:c:func:`drm_plane_cleanup()`), encoders
> >>> -(:c:func:`drm_encoder_cleanup()`) and connectors
> >>> -(:c:func:`drm_connector_cleanup()`). Furthermore, connectors that
> >>> -have been added to sysfs must be removed by a call to
> >>> -:c:func:`drm_connector_unregister()` before calling
> >>> -:c:func:`drm_connector_cleanup()`.
> >>> -
> >>> -Connectors state change detection must be cleanup up with a call to
> >>> -:c:func:`drm_kms_helper_poll_fini()`.
> >>> -
> >>> -Output discovery and initialization example
> >>> --------------------------------------------
> >>> -
> >>> -.. code-block:: c
> >>> -
> >>> -    void intel_crt_init(struct drm_device *dev)
> >>> -    {
> >>> -        struct drm_connector *connector;
> >>> -        struct intel_output *intel_output;
> >>> -
> >>> -        intel_output = kzalloc(sizeof(struct intel_output), GFP_KERNEL);
> >>> -        if (!intel_output)
> >>> -            return;
> >>> -
> >>> -        connector = &intel_output->base;
> >>> -        drm_connector_init(dev, &intel_output->base,
> >>> -                   &intel_crt_connector_funcs, DRM_MODE_CONNECTOR_VGA);
> >>> -
> >>> -        drm_encoder_init(dev, &intel_output->enc, &intel_crt_enc_funcs,
> >>> -                 DRM_MODE_ENCODER_DAC);
> >>> -
> >>> -        drm_connector_attach_encoder(&intel_output->base,
> >>> -                          &intel_output->enc);
> >>> -
> >>> -        /* Set up the DDC bus. */
> >>> -        intel_output->ddc_bus = intel_i2c_create(dev, GPIOA, "CRTDDC_A");
> >>> -        if (!intel_output->ddc_bus) {
> >>> -            dev_printk(KERN_ERR, &dev->pdev->dev, "DDC bus registration "
> >>> -                   "failed.\n");
> >>> -            return;
> >>> -        }
> >>> -
> >>> -        intel_output->type = INTEL_OUTPUT_ANALOG;
> >>> -        connector->interlace_allowed = 0;
> >>> -        connector->doublescan_allowed = 0;
> >>> -
> >>> -        drm_encoder_helper_add(&intel_output->enc, &intel_crt_helper_funcs);
> >>> -        drm_connector_helper_add(connector, &intel_crt_connector_helper_funcs);
> >>> -
> >>> -        drm_connector_register(connector);
> >>> -    }
> >>> -
> >>> -In the example above (taken from the i915 driver), a CRTC, connector and
> >>> -encoder combination is created. A device-specific i2c bus is also
> >>> -created for fetching EDID data and performing monitor detection. Once
> >>> -the process is complete, the new connector is registered with sysfs to
> >>> -make its properties available to applications.
> >>> -
> >>>    KMS Locking
> >>>    ===========
> >>>    
> >>>
> >>
> >> Everything else looks fine to drop.
> >>
> >> The bits about initialization/cleanup/subclassing/connectors can all be
> >> found in the Atomic Mode Setting section or one of the abstraction sections.
> > 
> > With the one thing you wanted to keep also wrong - ok with this patch?
> > 
> > Thanks for taking a look at this.
> > -Daniel
> > 
> 
> Sounds good.
> 
> Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@xxxxxxx>

Thanks for reviewing, patch merged to drm-misc-next.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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