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+// SPDX-License-Identifier: GPL-2.0
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+/*
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+ * (C) COPYRIGHT 2016 ARM Limited. All rights reserved.
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+ * Author: Brian Starkey <brian.starkey@arm.com>
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+ *
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+ * This program is free software and is provided to you under the terms of the
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+ * GNU General Public License version 2 as published by the Free Software
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+ * Foundation, and any use by you of this program is subject to the terms
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+ * of such GNU licence.
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+ */
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+
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+#include <drm/drm_crtc.h>
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+#include <drm/drm_modeset_helper_vtables.h>
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+#include <drm/drm_property.h>
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+#include <drm/drm_writeback.h>
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+#include <drm/drmP.h>
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+
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+/**
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+ * DOC: overview
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+ *
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+ * Writeback connectors are used to expose hardware which can write the output
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+ * from a CRTC to a memory buffer. They are used and act similarly to other
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+ * types of connectors, with some important differences:
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+ * - Writeback connectors don't provide a way to output visually to the user.
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+ * - Writeback connectors should always report as "disconnected" (so that
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+ * clients which don't understand them will ignore them).
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+ * - Writeback connectors don't have EDID.
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+ *
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+ * A framebuffer may only be attached to a writeback connector when the
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+ * connector is attached to a CRTC. The WRITEBACK_FB_ID property which sets the
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+ * framebuffer applies only to a single commit (see below). A framebuffer may
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+ * not be attached while the CRTC is off.
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+ *
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+ * Writeback connectors have some additional properties, which userspace
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+ * can use to query and control them:
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+ *
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+ * "WRITEBACK_FB_ID":
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+ * Write-only object property storing a DRM_MODE_OBJECT_FB: it stores the
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+ * framebuffer to be written by the writeback connector. This property is
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+ * similar to the FB_ID property on planes, but will always read as zero
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+ * and is not preserved across commits.
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+ * Userspace must set this property to an output buffer every time it
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+ * wishes the buffer to get filled.
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+ *
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+ * "WRITEBACK_PIXEL_FORMATS":
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+ * Immutable blob property to store the supported pixel formats table. The
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+ * data is an array of u32 DRM_FORMAT_* fourcc values.
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+ * Userspace can use this blob to find out what pixel formats are supported
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+ * by the connector's writeback engine.
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+ */
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+
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+static int create_writeback_properties(struct drm_device *dev)
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+{
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+ struct drm_property *prop;
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+
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+ if (!dev->mode_config.writeback_fb_id_property) {
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+ prop = drm_property_create_object(dev, DRM_MODE_PROP_ATOMIC,
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+ "WRITEBACK_FB_ID",
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+ DRM_MODE_OBJECT_FB);
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+ if (!prop)
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+ return -ENOMEM;
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+ dev->mode_config.writeback_fb_id_property = prop;
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+ }
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+
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+ if (!dev->mode_config.writeback_pixel_formats_property) {
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+ prop = drm_property_create(dev, DRM_MODE_PROP_BLOB |
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+ DRM_MODE_PROP_ATOMIC |
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+ DRM_MODE_PROP_IMMUTABLE,
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+ "WRITEBACK_PIXEL_FORMATS", 0);
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+ if (!prop)
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+ return -ENOMEM;
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+ dev->mode_config.writeback_pixel_formats_property = prop;
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+ }
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+
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+ return 0;
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+}
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+
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+static const struct drm_encoder_funcs drm_writeback_encoder_funcs = {
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+ .destroy = drm_encoder_cleanup,
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+};
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+
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+/**
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+ * drm_writeback_connector_init - Initialize a writeback connector and its properties
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+ * @dev: DRM device
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+ * @wb_connector: Writeback connector to initialize
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+ * @con_funcs: Connector funcs vtable
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+ * @enc_helper_funcs: Encoder helper funcs vtable to be used by the internal encoder
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+ * @formats: Array of supported pixel formats for the writeback engine
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+ * @n_formats: Length of the formats array
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+ *
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+ * This function creates the writeback-connector-specific properties if they
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+ * have not been already created, initializes the connector as
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+ * type DRM_MODE_CONNECTOR_WRITEBACK, and correctly initializes the property
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+ * values. It will also create an internal encoder associated with the
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+ * drm_writeback_connector and set it to use the @enc_helper_funcs vtable for
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+ * the encoder helper.
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+ *
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+ * Drivers should always use this function instead of drm_connector_init() to
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+ * set up writeback connectors.
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+ *
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+ * Returns: 0 on success, or a negative error code
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+ */
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+int drm_writeback_connector_init(struct drm_device *dev,
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+ struct drm_writeback_connector *wb_connector,
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+ const struct drm_connector_funcs *con_funcs,
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+ const struct drm_encoder_helper_funcs *enc_helper_funcs,
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+ const u32 *formats, int n_formats)
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+{
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+ struct drm_property_blob *blob;
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+ struct drm_connector *connector = &wb_connector->base;
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+ struct drm_mode_config *config = &dev->mode_config;
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+ int ret = create_writeback_properties(dev);
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+
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+ if (ret != 0)
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+ return ret;
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+
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+ blob = drm_property_create_blob(dev, n_formats * sizeof(*formats),
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+ formats);
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+ if (IS_ERR(blob))
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+ return PTR_ERR(blob);
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+
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+ drm_encoder_helper_add(&wb_connector->encoder, enc_helper_funcs);
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+ ret = drm_encoder_init(dev, &wb_connector->encoder,
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+ &drm_writeback_encoder_funcs,
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+ DRM_MODE_ENCODER_VIRTUAL, NULL);
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+ if (ret)
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+ goto fail;
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+
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+ connector->interlace_allowed = 0;
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+
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+ ret = drm_connector_init(dev, connector, con_funcs,
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+ DRM_MODE_CONNECTOR_WRITEBACK);
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+ if (ret)
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+ goto connector_fail;
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+
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+ ret = drm_mode_connector_attach_encoder(connector,
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+ &wb_connector->encoder);
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+ if (ret)
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+ goto attach_fail;
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+
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+ INIT_LIST_HEAD(&wb_connector->job_queue);
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+ spin_lock_init(&wb_connector->job_lock);
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+
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+ drm_object_attach_property(&connector->base,
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+ config->writeback_fb_id_property, 0);
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+
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+ drm_object_attach_property(&connector->base,
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+ config->writeback_pixel_formats_property,
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+ blob->base.id);
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+ wb_connector->pixel_formats_blob_ptr = blob;
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+
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+ return 0;
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+
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+attach_fail:
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+ drm_connector_cleanup(connector);
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+connector_fail:
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+ drm_encoder_cleanup(&wb_connector->encoder);
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+fail:
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+ drm_property_blob_put(blob);
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+ return ret;
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+}
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+EXPORT_SYMBOL(drm_writeback_connector_init);
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+
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+/**
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+ * drm_writeback_queue_job - Queue a writeback job for later signalling
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+ * @wb_connector: The writeback connector to queue a job on
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+ * @job: The job to queue
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+ *
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+ * This function adds a job to the job_queue for a writeback connector. It
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+ * should be considered to take ownership of the writeback job, and so any other
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+ * references to the job must be cleared after calling this function.
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+ *
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+ * Drivers must ensure that for a given writeback connector, jobs are queued in
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+ * exactly the same order as they will be completed by the hardware (and
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+ * signaled via drm_writeback_signal_completion).
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+ *
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+ * For every call to drm_writeback_queue_job() there must be exactly one call to
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+ * drm_writeback_signal_completion()
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+ *
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+ * See also: drm_writeback_signal_completion()
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+ */
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+void drm_writeback_queue_job(struct drm_writeback_connector *wb_connector,
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+ struct drm_writeback_job *job)
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+{
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+ unsigned long flags;
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+
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+ spin_lock_irqsave(&wb_connector->job_lock, flags);
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+ list_add_tail(&job->list_entry, &wb_connector->job_queue);
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+ spin_unlock_irqrestore(&wb_connector->job_lock, flags);
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+}
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+EXPORT_SYMBOL(drm_writeback_queue_job);
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+
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+/*
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+ * @cleanup_work: deferred cleanup of a writeback job
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+ *
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+ * The job cannot be cleaned up directly in drm_writeback_signal_completion,
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+ * because it may be called in interrupt context. Dropping the framebuffer
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+ * reference can sleep, and so the cleanup is deferred to a workqueue.
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+ */
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+static void cleanup_work(struct work_struct *work)
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+{
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+ struct drm_writeback_job *job = container_of(work,
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+ struct drm_writeback_job,
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+ cleanup_work);
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+ drm_framebuffer_put(job->fb);
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+ kfree(job);
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+}
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+
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+
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+/**
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+ * drm_writeback_signal_completion - Signal the completion of a writeback job
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+ * @wb_connector: The writeback connector whose job is complete
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+ *
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+ * Drivers should call this to signal the completion of a previously queued
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+ * writeback job. It should be called as soon as possible after the hardware
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+ * has finished writing, and may be called from interrupt context.
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+ * It is the driver's responsibility to ensure that for a given connector, the
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+ * hardware completes writeback jobs in the same order as they are queued.
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+ *
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+ * Unless the driver is holding its own reference to the framebuffer, it must
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+ * not be accessed after calling this function.
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+ *
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+ * See also: drm_writeback_queue_job()
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+ */
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+void
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+drm_writeback_signal_completion(struct drm_writeback_connector *wb_connector)
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+{
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+ unsigned long flags;
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+ struct drm_writeback_job *job;
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+
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+ spin_lock_irqsave(&wb_connector->job_lock, flags);
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+ job = list_first_entry_or_null(&wb_connector->job_queue,
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+ struct drm_writeback_job,
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+ list_entry);
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+ if (job)
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+ list_del(&job->list_entry);
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+ spin_unlock_irqrestore(&wb_connector->job_lock, flags);
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+
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+ if (WARN_ON(!job))
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+ return;
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+
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+ INIT_WORK(&job->cleanup_work, cleanup_work);
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+ queue_work(system_long_wq, &job->cleanup_work);
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+}
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+EXPORT_SYMBOL(drm_writeback_signal_completion);
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Brian Starkey