Re: [PATCH v2 6/6] drm: Add helper for simple display pipeline

[Daniel Vetter]

On Wed, May 11, 2016 at 06:09:22PM +0200, Noralf Trønnes wrote:
> Provides helper functions for drivers that have a simple display
> pipeline. Plane, crtc and encoder are collapsed into one entity.
> 
> Signed-off-by: Noralf Trønnes <noralf@xxxxxxxxxxx>

Looks really nice, just a few suggestions for the kerneldoc. Would be
awesome if we could get an ack on this from Jyri for tilcdc, but even
without that I think I'll just pull in the next iteration. Still please cc
him.

Thanks, Daniel

> ---
> 
> Changes since v1:
> - Add DOC header and add to gpu.tmpl
> - Fix docs: @funcs is optional, "negative error code",
>   "This hook is optional."
> - Add checks to drm_simple_kms_plane_atomic_check()
> 
>  Documentation/DocBook/gpu.tmpl          |   6 +
>  drivers/gpu/drm/Kconfig                 |   7 ++
>  drivers/gpu/drm/Makefile                |   1 +
>  drivers/gpu/drm/drm_simple_kms_helper.c | 200 ++++++++++++++++++++++++++++++++
>  include/drm/drm_simple_kms_helper.h     |  92 +++++++++++++++
>  5 files changed, 306 insertions(+)
>  create mode 100644 drivers/gpu/drm/drm_simple_kms_helper.c
>  create mode 100644 include/drm/drm_simple_kms_helper.h
> 
> diff --git a/Documentation/DocBook/gpu.tmpl b/Documentation/DocBook/gpu.tmpl
> index 4a0c599..cf3f5a8 100644
> --- a/Documentation/DocBook/gpu.tmpl
> +++ b/Documentation/DocBook/gpu.tmpl
> @@ -1693,6 +1693,12 @@ void intel_crt_init(struct drm_device *dev)
>  !Edrivers/gpu/drm/drm_panel.c
>  !Pdrivers/gpu/drm/drm_panel.c drm panel
>      </sect2>
> +    <sect2>
> +      <title>Simple KMS Helper Reference</title>
> +!Iinclude/drm/drm_simple_kms_helper.h
> +!Edrivers/gpu/drm/drm_simple_kms_helper.c
> +!Pdrivers/gpu/drm/drm_simple_kms_helper.c overview
> +    </sect2>
>    </sect1>
> 
>    <!-- Internals: kms properties -->
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index 16e4c21..ff9f480 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -39,6 +39,13 @@ config DRM_KMS_HELPER
>  	help
>  	  CRTC helpers for KMS drivers.
> 
> +config DRM_SIMPLE_KMS_HELPER
> +	tristate
> +	depends on DRM
> +	select DRM_KMS_HELPER
> +	help
> +	  Helpers for very simple KMS drivers.

Personally not sold on piles of Kconfig knobs for tiny amounts of code
like this one. I'd just drop it. For a more elaborate argument see

http://sietch-tagr.blogspot.ch/2016/04/display-panels-are-not-special.html

Note that almost all the other helpers do not have a Kconfig option, the
only real exception is the fbdev helpers. And those have a good reason:
They'd drag in all of fbdev, and that is actually a pile of code.

> +
>  config DRM_KMS_FB_HELPER
>  	bool
>  	depends on DRM_KMS_HELPER
> diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
> index 43c2abf..7e99923 100644
> --- a/drivers/gpu/drm/Makefile
> +++ b/drivers/gpu/drm/Makefile
> @@ -31,6 +31,7 @@ drm_kms_helper-$(CONFIG_DRM_KMS_CMA_HELPER) += drm_fb_cma_helper.o
>  drm_kms_helper-$(CONFIG_DRM_DP_AUX_CHARDEV) += drm_dp_aux_dev.o
> 
>  obj-$(CONFIG_DRM_KMS_HELPER) += drm_kms_helper.o
> +obj-$(CONFIG_DRM_SIMPLE_KMS_HELPER) += drm_simple_kms_helper.o
> 
>  CFLAGS_drm_trace_points.o := -I$(src)
> 
> diff --git a/drivers/gpu/drm/drm_simple_kms_helper.c b/drivers/gpu/drm/drm_simple_kms_helper.c
> new file mode 100644
> index 0000000..64bf0f2
> --- /dev/null
> +++ b/drivers/gpu/drm/drm_simple_kms_helper.c
> @@ -0,0 +1,200 @@
> +/*
> + * Copyright (C) 2016 Noralf Trønnes
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + */
> +
> +#include <drm/drmP.h>
> +#include <drm/drm_atomic.h>
> +#include <drm/drm_atomic_helper.h>
> +#include <drm/drm_crtc_helper.h>
> +#include <drm/drm_plane_helper.h>
> +#include <drm/drm_simple_kms_helper.h>
> +#include <linux/slab.h>
> +
> +/**
> + * DOC: overview
> + *
> + * This helper library provides helpers for simple drivers.

"drivers for simple display hardware" is imo clearer.

> + *
> + * drm_simple_display_pipe_init() initializes a simple display pipeline
> + * consisting of a plane-crtc-encoder pipe coupled with a connector.

Hm, I think a bit more text here would be useful.

"drm_simple_display_pipe_init() initializes a simple display pipeline
which has only one full-screen scanout buffer feeding one output. The
pipeline is represented by struct &drm_simple_display_pipe and binds
together &drm_plane, &drm_crtc and &drm_encoder structures into one fixed
entity. Some flexibility for code reuse is provided through a separately
allocated &drm_connector object and supporting optional &drm_bridge
encoder drivers.

> + */
> +
> +static const struct drm_encoder_funcs drm_simple_kms_encoder_funcs = {
> +	.destroy = drm_encoder_cleanup,
> +};
> +
> +static void drm_simple_kms_crtc_enable(struct drm_crtc *crtc)
> +{
> +	struct drm_simple_display_pipe *pipe;
> +
> +	pipe = container_of(crtc, struct drm_simple_display_pipe, crtc);
> +	if (!pipe->funcs || !pipe->funcs->enable)
> +		return;
> +
> +	pipe->funcs->enable(pipe, crtc->state);
> +}
> +
> +static void drm_simple_kms_crtc_disable(struct drm_crtc *crtc)
> +{
> +	struct drm_simple_display_pipe *pipe;
> +
> +	pipe = container_of(crtc, struct drm_simple_display_pipe, crtc);
> +	if (!pipe->funcs || !pipe->funcs->disable)
> +		return;
> +
> +	pipe->funcs->disable(pipe);
> +}
> +
> +static const struct drm_crtc_helper_funcs drm_simple_kms_crtc_helper_funcs = {
> +	.disable = drm_simple_kms_crtc_disable,
> +	.enable = drm_simple_kms_crtc_enable,
> +};
> +
> +static const struct drm_crtc_funcs drm_simple_kms_crtc_funcs = {
> +	.reset = drm_atomic_helper_crtc_reset,
> +	.destroy = drm_crtc_cleanup,
> +	.set_config = drm_atomic_helper_set_config,
> +	.page_flip = drm_atomic_helper_page_flip,
> +	.atomic_duplicate_state = drm_atomic_helper_crtc_duplicate_state,
> +	.atomic_destroy_state = drm_atomic_helper_crtc_destroy_state,
> +};
> +
> +static int drm_simple_kms_plane_atomic_check(struct drm_plane *plane,
> +					struct drm_plane_state *plane_state)
> +{
> +	struct drm_rect src = {
> +		.x1 = plane_state->src_x,
> +		.y1 = plane_state->src_y,
> +		.x2 = plane_state->src_x + plane_state->src_w,
> +		.y2 = plane_state->src_y + plane_state->src_h,
> +	};
> +	struct drm_rect dest = {
> +		.x1 = plane_state->crtc_x,
> +		.y1 = plane_state->crtc_y,
> +		.x2 = plane_state->crtc_x + plane_state->crtc_w,
> +		.y2 = plane_state->crtc_y + plane_state->crtc_h,
> +	};
> +	struct drm_rect clip = { 0 };
> +	struct drm_simple_display_pipe *pipe;
> +	struct drm_crtc_state *crtc_state;
> +	bool visible;
> +	int ret;
> +
> +	pipe = container_of(plane, struct drm_simple_display_pipe, plane);
> +	crtc_state = drm_atomic_get_existing_crtc_state(plane_state->state,
> +							&pipe->crtc);
> +	if (crtc_state->enable != !!plane_state->crtc)
> +		return -EINVAL; /* plane must match crtc enable state */
> +
> +	if (!crtc_state->enable)
> +		return 0; /* nothing to check when disabling or disabled */
> +
> +	clip.x2 = crtc_state->adjusted_mode.hdisplay;
> +	clip.y2 = crtc_state->adjusted_mode.vdisplay;
> +	ret = drm_plane_helper_check_update(plane, &pipe->crtc,
> +					    plane_state->fb,
> +					    &src, &dest, &clip,
> +					    DRM_PLANE_HELPER_NO_SCALING,
> +					    DRM_PLANE_HELPER_NO_SCALING,
> +					    false, true, &visible);
> +	if (ret)
> +		return ret;
> +
> +	if (!visible)
> +		return -EINVAL;

I think the logic above looks correct now, but might be worth checking
with your driver that it doesn't let something silly through. I.e. a small
test app that tries to reposition the primary plane, or tries to disable
it while the crtc is on. We should have that somewhere in libdrm I think.

> +
> +	if (!pipe->funcs || !pipe->funcs->check)
> +		return 0;
> +
> +	return pipe->funcs->check(pipe, plane_state, crtc_state);
> +}
> +
> +static void drm_simple_kms_plane_atomic_update(struct drm_plane *plane,
> +					struct drm_plane_state *pstate)
> +{
> +	struct drm_simple_display_pipe *pipe;
> +
> +	pipe = container_of(plane, struct drm_simple_display_pipe, plane);
> +	if (!pipe->funcs || !pipe->funcs->update)
> +		return;
> +
> +	pipe->funcs->update(pipe, pstate);
> +}
> +
> +static const struct drm_plane_helper_funcs drm_simple_kms_plane_helper_funcs = {
> +	.atomic_check = drm_simple_kms_plane_atomic_check,
> +	.atomic_update = drm_simple_kms_plane_atomic_update,
> +};
> +
> +static const struct drm_plane_funcs drm_simple_kms_plane_funcs = {
> +	.update_plane		= drm_atomic_helper_update_plane,
> +	.disable_plane		= drm_atomic_helper_disable_plane,
> +	.destroy		= drm_plane_cleanup,
> +	.reset			= drm_atomic_helper_plane_reset,
> +	.atomic_duplicate_state	= drm_atomic_helper_plane_duplicate_state,
> +	.atomic_destroy_state	= drm_atomic_helper_plane_destroy_state,
> +};
> +
> +/**
> + * drm_simple_display_pipe_init - Initialize a simple display pipeline
> + * @dev: DRM device
> + * @pipe: simple display pipe object to initialize
> + * @funcs: callbacks for the display pipe (optional)
> + * @formats: array of supported formats (%DRM_FORMAT_*)
> + * @format_count: number of elements in @formats
> + * @connector: connector to attach and register
> + *
> + * Sets up a display pipeline which consist of a really simple
> + * plane-crtc-encoder pipe coupled with the provided connector.

How are drivers supposed to release this stuff again? Maybe add:

"Teardown of a simple display pipe is all handled automatically by the drm
core through calling drm_mode_config_cleanup()."

> + *
> + * Returns:
> + * Zero on success, negative error code on failure.
> + */
> +int drm_simple_display_pipe_init(struct drm_device *dev,
> +				 struct drm_simple_display_pipe *pipe,
> +				 struct drm_simple_display_pipe_funcs *funcs,
> +				 const uint32_t *formats,
> +				 unsigned int format_count,
> +				 struct drm_connector *connector)
> +{
> +	struct drm_encoder *encoder = &pipe->encoder;
> +	struct drm_plane *plane = &pipe->plane;
> +	struct drm_crtc *crtc = &pipe->crtc;
> +	int ret;
> +
> +	pipe->funcs = funcs;
> +
> +	drm_plane_helper_add(plane, &drm_simple_kms_plane_helper_funcs);
> +	ret = drm_universal_plane_init(dev, plane, 0,
> +				       &drm_simple_kms_plane_funcs,
> +				       formats, format_count,
> +				       DRM_PLANE_TYPE_PRIMARY, NULL);
> +	if (ret)
> +		return ret;
> +
> +	drm_crtc_helper_add(crtc, &drm_simple_kms_crtc_helper_funcs);
> +	ret = drm_crtc_init_with_planes(dev, crtc, plane, NULL,
> +					&drm_simple_kms_crtc_funcs, NULL);
> +	if (ret)
> +		return ret;
> +
> +	encoder->possible_crtcs = 1 << drm_crtc_index(crtc);
> +	ret = drm_encoder_init(dev, encoder, &drm_simple_kms_encoder_funcs,
> +			       DRM_MODE_ENCODER_NONE, NULL);
> +	if (ret)
> +		return ret;
> +
> +	ret = drm_mode_connector_attach_encoder(connector, encoder);
> +	if (ret)
> +		return ret;
> +
> +	return drm_connector_register(connector);
> +}
> +EXPORT_SYMBOL(drm_simple_display_pipe_init);
> +
> +MODULE_LICENSE("GPL");
> diff --git a/include/drm/drm_simple_kms_helper.h b/include/drm/drm_simple_kms_helper.h
> new file mode 100644
> index 0000000..ef578f4
> --- /dev/null
> +++ b/include/drm/drm_simple_kms_helper.h
> @@ -0,0 +1,92 @@
> +/*
> + * Copyright (C) 2016 Noralf Trønnes
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + */
> +
> +#ifndef __LINUX_DRM_SIMPLE_KMS_HELPER_H
> +#define __LINUX_DRM_SIMPLE_KMS_HELPER_H
> +
> +struct drm_simple_display_pipe;
> +
> +/**
> + * struct drm_simple_display_pipe_funcs - helper operations for a simple
> + *                                        display pipeline
> + */
> +struct drm_simple_display_pipe_funcs {
> +	/**
> +	 * @enable:
> +	 *
> +	 * This function should be used to enable the pipeline.
> +	 * It is called when the underlying crtc is enabled.
> +	 * This hook is optional.
> +	 */
> +	void (*enable)(struct drm_simple_display_pipe *pipe,
> +		       struct drm_crtc_state *crtc_state);
> +	/**
> +	 * @disable:
> +	 *
> +	 * This function should be used to disable the pipeline.
> +	 * It is called when the underlying crtc is disabled.
> +	 * This hook is optional.
> +	 */
> +	void (*disable)(struct drm_simple_display_pipe *pipe);
> +
> +	/**
> +	 * @check:
> +	 *
> +	 * This function is called in the check phase of an atomic update,
> +	 * specifically when the underlying plane is checked.

I think we need to clarify a bit more what the helpers check already:

"The simple display pipeline helpers already check that the plane is not
scaled, fills the entire visible area and is always enabled when the crtc
is also enabled."

> +	 * This hook is optional.
> +	 *
> +	 * RETURNS:
> +	 *
> +	 * 0 on success, -EINVAL if the state or the transition can't be
> +	 * supported, -ENOMEM on memory allocation failure and -EDEADLK if an
> +	 * attempt to obtain another state object ran into a &drm_modeset_lock
> +	 * deadlock.
> +	 */
> +	int (*check)(struct drm_simple_display_pipe *pipe,
> +		     struct drm_plane_state *plane_state,
> +		     struct drm_crtc_state *crtc_state);
> +	/**
> +	 * @update:
> +	 *
> +	 * This function is called when the underlying plane state is updated.
> +	 * This hook is optional.
> +	 */
> +	void (*update)(struct drm_simple_display_pipe *pipe,
> +		       struct drm_plane_state *plane_state);
> +};
> +
> +/**
> + * struct drm_simple_display_pipe - simple display pipeline
> + * @crtc: CRTC control structure
> + * @plane: Plane control structure
> + * @encoder: Encoder control structure
> + * @connector: Connector control structure
> + * @funcs: Pipeline control functions (optional)
> + *
> + * Simple display pipeline with plane, crtc and encoder collapsed into one
> + * entity.

Maybe add: "It should be initialized by calling
drm_simple_display_pipe_init()". Imo never hurts to have a few too many
cross references ;-)

> + */
> +struct drm_simple_display_pipe {
> +	struct drm_crtc crtc;
> +	struct drm_plane plane;
> +	struct drm_encoder encoder;
> +	struct drm_connector *connector;
> +
> +	struct drm_simple_display_pipe_funcs *funcs;
> +};
> +
> +int drm_simple_display_pipe_init(struct drm_device *dev,
> +				 struct drm_simple_display_pipe *pipe,
> +				 struct drm_simple_display_pipe_funcs *funcs,
> +				 const uint32_t *formats,
> +				 unsigned int format_count,
> +				 struct drm_connector *connector);
> +
> +#endif /* __LINUX_DRM_SIMPLE_KMS_HELPER_H */
> --
> 2.8.2
> 

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