linux-kernel - Re: [PATCH v2 11/11] drm/todo: Remove the drm_atomic

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Message-ID: <CAKMK7uHEnsZty40YOc+ySDwJLkGWm0aPaTKDvecnymVX4yLjAA@mail.gmail.com>
Date:   Thu, 21 Jan 2021 19:27:25 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Daniel Vetter <daniel.vetter@...el.com>,
        David Airlie <airlied@...ux.ie>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Maxime Ripard <mripard@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 11/11] drm/todo: Remove the drm_atomic_state todo item

On Thu, Jan 21, 2021 at 5:36 PM Maxime Ripard <maxime@...no.tech> wrote:
>
> Only planes' prepare_fb and cleanup_fb, and encoders' atomic_check and
> atomic_mode_set hooks remain with an object state and not the global
> drm_atomic_state.
>
> prepare_fb and cleanup_fb operate by design on a given state and
> depending on the calling site can operate on either the old or new
> state, so it doesn't really make much sense to convert them.
>
> The encoders' atomic_check and atomic_mode_set operate on the CRTC and
> connector state connected to them since encoders don't have a state of
> their own. Without those state pointers, we would need to get the CRTC
> through the drm_connector_state crtc pointer.
>
> However, in order to get the drm_connector_state pointer, we would need
> to get the connector itself and while usually we have a single connector
> connected to the encoder, we can't really get it from the encoder at
> the moment since it could be behind any number of bridges.
>
> While this could be addressed by (for example) listing all the
> connectors and finding the one that has the encoder as its source, it
> feels like an unnecessary rework for something that is slowly getting
> replaced by bridges.
>
> Since all the users that matter have been converted, let's remove the
> TODO item.
>
> Signed-off-by: Maxime Ripard <maxime@...no.tech>

Acked-by: Daniel Vetter <daniel.vetter@...ll.ch>

>
> ---
>
> Changes from v1:
>   - New patch
> ---
>  Documentation/gpu/todo.rst | 46 --------------------------------------
>  1 file changed, 46 deletions(-)
>
> diff --git a/Documentation/gpu/todo.rst b/Documentation/gpu/todo.rst
> index 009d8e6c7e3c..609794108f5a 100644
> --- a/Documentation/gpu/todo.rst
> +++ b/Documentation/gpu/todo.rst
> @@ -440,52 +440,6 @@ Contact: Emil Velikov, respective driver maintainers
>
>  Level: Intermediate
>
> -Plumb drm_atomic_state all over
> --------------------------------
> -
> -Currently various atomic functions take just a single or a handful of
> -object states (eg. plane state). While that single object state can
> -suffice for some simple cases, we often have to dig out additional
> -object states for dealing with various dependencies between the individual
> -objects or the hardware they represent. The process of digging out the
> -additional states is rather non-intuitive and error prone.
> -
> -To fix that most functions should rather take the overall
> -drm_atomic_state as one of their parameters. The other parameters
> -would generally be the object(s) we mainly want to interact with.
> -
> -For example, instead of
> -
> -.. code-block:: c
> -
> -   int (*atomic_check)(struct drm_plane *plane, struct drm_plane_state *state);
> -
> -we would have something like
> -
> -.. code-block:: c
> -
> -   int (*atomic_check)(struct drm_plane *plane, struct drm_atomic_state *state);
> -
> -The implementation can then trivially gain access to any required object
> -state(s) via drm_atomic_get_plane_state(), drm_atomic_get_new_plane_state(),
> -drm_atomic_get_old_plane_state(), and their equivalents for
> -other object types.
> -
> -Additionally many drivers currently access the object->state pointer
> -directly in their commit functions. That is not going to work if we
> -eg. want to allow deeper commit pipelines as those pointers could
> -then point to the states corresponding to a future commit instead of
> -the current commit we're trying to process. Also non-blocking commits
> -execute locklessly so there are serious concerns with dereferencing
> -the object->state pointers without holding the locks that protect them.
> -Use of drm_atomic_get_new_plane_state(), drm_atomic_get_old_plane_state(),
> -etc. avoids these problems as well since they relate to a specific
> -commit via the passed in drm_atomic_state.
> -
> -Contact: Ville Syrjälä, Daniel Vetter
> -
> -Level: Intermediate
> -
>  Use struct dma_buf_map throughout codebase
>  ------------------------------------------
>
> --
> 2.29.2
>


-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch