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

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@tronnes.org

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