blob: 43d9e3bb3a94344fd81d7886ec6c2d412d9b7db1 [file] [log] [blame]
// SPDX-License-Identifier: GPL-2.0
* (C) COPYRIGHT 2016 ARM Limited. All rights reserved.
* Author: Brian Starkey <>
* This program is free software and is provided to you under the terms of the
* GNU General Public License version 2 as published by the Free Software
* Foundation, and any use by you of this program is subject to the terms
* of such GNU licence.
#include <linux/dma-fence.h>
#include <drm/drm_crtc.h>
#include <drm/drm_device.h>
#include <drm/drm_drv.h>
#include <drm/drm_modeset_helper_vtables.h>
#include <drm/drm_property.h>
#include <drm/drm_writeback.h>
* DOC: overview
* Writeback connectors are used to expose hardware which can write the output
* from a CRTC to a memory buffer. They are used and act similarly to other
* types of connectors, with some important differences:
* * Writeback connectors don't provide a way to output visually to the user.
* * Writeback connectors are visible to userspace only when the client sets
* * Writeback connectors don't have EDID.
* A framebuffer may only be attached to a writeback connector when the
* connector is attached to a CRTC. The WRITEBACK_FB_ID property which sets the
* framebuffer applies only to a single commit (see below). A framebuffer may
* not be attached while the CRTC is off.
* Unlike with planes, when a writeback framebuffer is removed by userspace DRM
* makes no attempt to remove it from active use by the connector. This is
* because no method is provided to abort a writeback operation, and in any
* case making a new commit whilst a writeback is ongoing is undefined (see
* WRITEBACK_OUT_FENCE_PTR below). As soon as the current writeback is finished,
* the framebuffer will automatically no longer be in active use. As it will
* also have already been removed from the framebuffer list, there will be no
* way for any userspace application to retrieve a reference to it in the
* intervening period.
* Writeback connectors have some additional properties, which userspace
* can use to query and control them:
* Write-only object property storing a DRM_MODE_OBJECT_FB: it stores the
* framebuffer to be written by the writeback connector. This property is
* similar to the FB_ID property on planes, but will always read as zero
* and is not preserved across commits.
* Userspace must set this property to an output buffer every time it
* wishes the buffer to get filled.
* Immutable blob property to store the supported pixel formats table. The
* data is an array of u32 DRM_FORMAT_* fourcc values.
* Userspace can use this blob to find out what pixel formats are supported
* by the connector's writeback engine.
* Userspace can use this property to provide a pointer for the kernel to
* fill with a sync_file file descriptor, which will signal once the
* writeback is finished. The value should be the address of a 32-bit
* signed integer, cast to a u64.
* Userspace should wait for this fence to signal before making another
* commit affecting any of the same CRTCs, Planes or Connectors.
* **Failure to do so will result in undefined behaviour.**
* For this reason it is strongly recommended that all userspace
* applications making use of writeback connectors *always* retrieve an
* out-fence for the commit and use it appropriately.
* From userspace, this property will always read as zero.
#define fence_to_wb_connector(x) container_of(x->lock, \
struct drm_writeback_connector, \
static const char *drm_writeback_fence_get_driver_name(struct dma_fence *fence)
struct drm_writeback_connector *wb_connector =
return wb_connector->>driver->name;
static const char *
drm_writeback_fence_get_timeline_name(struct dma_fence *fence)
struct drm_writeback_connector *wb_connector =
return wb_connector->timeline_name;
static bool drm_writeback_fence_enable_signaling(struct dma_fence *fence)
return true;
static const struct dma_fence_ops drm_writeback_fence_ops = {
.get_driver_name = drm_writeback_fence_get_driver_name,
.get_timeline_name = drm_writeback_fence_get_timeline_name,
.enable_signaling = drm_writeback_fence_enable_signaling,
.wait = dma_fence_default_wait,
static int create_writeback_properties(struct drm_device *dev)
struct drm_property *prop;
if (!dev->mode_config.writeback_fb_id_property) {
prop = drm_property_create_object(dev, DRM_MODE_PROP_ATOMIC,
if (!prop)
return -ENOMEM;
dev->mode_config.writeback_fb_id_property = prop;
if (!dev->mode_config.writeback_pixel_formats_property) {
prop = drm_property_create(dev, DRM_MODE_PROP_BLOB |
if (!prop)
return -ENOMEM;
dev->mode_config.writeback_pixel_formats_property = prop;
if (!dev->mode_config.writeback_out_fence_ptr_property) {
prop = drm_property_create_range(dev, DRM_MODE_PROP_ATOMIC,
if (!prop)
return -ENOMEM;
dev->mode_config.writeback_out_fence_ptr_property = prop;
return 0;
static const struct drm_encoder_funcs drm_writeback_encoder_funcs = {
.destroy = drm_encoder_cleanup,
* drm_writeback_connector_init - Initialize a writeback connector and its properties
* @dev: DRM device
* @wb_connector: Writeback connector to initialize
* @con_funcs: Connector funcs vtable
* @enc_helper_funcs: Encoder helper funcs vtable to be used by the internal encoder
* @formats: Array of supported pixel formats for the writeback engine
* @n_formats: Length of the formats array
* This function creates the writeback-connector-specific properties if they
* have not been already created, initializes the connector as
* type DRM_MODE_CONNECTOR_WRITEBACK, and correctly initializes the property
* values. It will also create an internal encoder associated with the
* drm_writeback_connector and set it to use the @enc_helper_funcs vtable for
* the encoder helper.
* Drivers should always use this function instead of drm_connector_init() to
* set up writeback connectors.
* Returns: 0 on success, or a negative error code
int drm_writeback_connector_init(struct drm_device *dev,
struct drm_writeback_connector *wb_connector,
const struct drm_connector_funcs *con_funcs,
const struct drm_encoder_helper_funcs *enc_helper_funcs,
const u32 *formats, int n_formats)
struct drm_property_blob *blob;
struct drm_connector *connector = &wb_connector->base;
struct drm_mode_config *config = &dev->mode_config;
int ret = create_writeback_properties(dev);
if (ret != 0)
return ret;
blob = drm_property_create_blob(dev, n_formats * sizeof(*formats),
if (IS_ERR(blob))
return PTR_ERR(blob);
drm_encoder_helper_add(&wb_connector->encoder, enc_helper_funcs);
ret = drm_encoder_init(dev, &wb_connector->encoder,
if (ret)
goto fail;
connector->interlace_allowed = 0;
ret = drm_connector_init(dev, connector, con_funcs,
if (ret)
goto connector_fail;
ret = drm_connector_attach_encoder(connector,
if (ret)
goto attach_fail;
wb_connector->fence_context = dma_fence_context_alloc(1);
"CONNECTOR:%d-%s", connector->, connector->name);
config->writeback_out_fence_ptr_property, 0);
config->writeback_fb_id_property, 0);
wb_connector->pixel_formats_blob_ptr = blob;
return 0;
return ret;
int drm_writeback_set_fb(struct drm_connector_state *conn_state,
struct drm_framebuffer *fb)
WARN_ON(conn_state->connector->connector_type != DRM_MODE_CONNECTOR_WRITEBACK);
if (!conn_state->writeback_job) {
conn_state->writeback_job =
kzalloc(sizeof(*conn_state->writeback_job), GFP_KERNEL);
if (!conn_state->writeback_job)
return -ENOMEM;
conn_state->writeback_job->connector =
drm_framebuffer_assign(&conn_state->writeback_job->fb, fb);
return 0;
int drm_writeback_prepare_job(struct drm_writeback_job *job)
struct drm_writeback_connector *connector = job->connector;
const struct drm_connector_helper_funcs *funcs =
int ret;
if (funcs->prepare_writeback_job) {
ret = funcs->prepare_writeback_job(connector, job);
if (ret < 0)
return ret;
job->prepared = true;
return 0;
* drm_writeback_queue_job - Queue a writeback job for later signalling
* @wb_connector: The writeback connector to queue a job on
* @conn_state: The connector state containing the job to queue
* This function adds the job contained in @conn_state to the job_queue for a
* writeback connector. It takes ownership of the writeback job and sets the
* @conn_state->writeback_job to NULL, and so no access to the job may be
* performed by the caller after this function returns.
* Drivers must ensure that for a given writeback connector, jobs are queued in
* exactly the same order as they will be completed by the hardware (and
* signaled via drm_writeback_signal_completion).
* For every call to drm_writeback_queue_job() there must be exactly one call to
* drm_writeback_signal_completion()
* See also: drm_writeback_signal_completion()
void drm_writeback_queue_job(struct drm_writeback_connector *wb_connector,
struct drm_connector_state *conn_state)
struct drm_writeback_job *job;
unsigned long flags;
job = conn_state->writeback_job;
conn_state->writeback_job = NULL;
spin_lock_irqsave(&wb_connector->job_lock, flags);
list_add_tail(&job->list_entry, &wb_connector->job_queue);
spin_unlock_irqrestore(&wb_connector->job_lock, flags);
void drm_writeback_cleanup_job(struct drm_writeback_job *job)
struct drm_writeback_connector *connector = job->connector;
const struct drm_connector_helper_funcs *funcs =
if (job->prepared && funcs->cleanup_writeback_job)
funcs->cleanup_writeback_job(connector, job);
if (job->fb)
if (job->out_fence)
* @cleanup_work: deferred cleanup of a writeback job
* The job cannot be cleaned up directly in drm_writeback_signal_completion,
* because it may be called in interrupt context. Dropping the framebuffer
* reference can sleep, and so the cleanup is deferred to a workqueue.
static void cleanup_work(struct work_struct *work)
struct drm_writeback_job *job = container_of(work,
struct drm_writeback_job,
* drm_writeback_signal_completion - Signal the completion of a writeback job
* @wb_connector: The writeback connector whose job is complete
* @status: Status code to set in the writeback out_fence (0 for success)
* Drivers should call this to signal the completion of a previously queued
* writeback job. It should be called as soon as possible after the hardware
* has finished writing, and may be called from interrupt context.
* It is the driver's responsibility to ensure that for a given connector, the
* hardware completes writeback jobs in the same order as they are queued.
* Unless the driver is holding its own reference to the framebuffer, it must
* not be accessed after calling this function.
* See also: drm_writeback_queue_job()
drm_writeback_signal_completion(struct drm_writeback_connector *wb_connector,
int status)
unsigned long flags;
struct drm_writeback_job *job;
struct dma_fence *out_fence;
spin_lock_irqsave(&wb_connector->job_lock, flags);
job = list_first_entry_or_null(&wb_connector->job_queue,
struct drm_writeback_job,
if (job)
spin_unlock_irqrestore(&wb_connector->job_lock, flags);
if (WARN_ON(!job))
out_fence = job->out_fence;
if (out_fence) {
if (status)
dma_fence_set_error(out_fence, status);
job->out_fence = NULL;
INIT_WORK(&job->cleanup_work, cleanup_work);
queue_work(system_long_wq, &job->cleanup_work);
struct dma_fence *
drm_writeback_get_out_fence(struct drm_writeback_connector *wb_connector)
struct dma_fence *fence;
if (WARN_ON(wb_connector->base.connector_type !=
return NULL;
fence = kzalloc(sizeof(*fence), GFP_KERNEL);
if (!fence)
return NULL;
dma_fence_init(fence, &drm_writeback_fence_ops,
&wb_connector->fence_lock, wb_connector->fence_context,
return fence;