[Intel-gfx] [RFC 05/12] drm/i915: Add a relay backed debugfs interface for capturing GuC logs

[akash.goel at intel.com]

From: Akash Goel <akash.goel at intel.com>

Added a new debugfs interface '/sys/kernel/debug/dri/guc_log' for the
User to capture GuC ukernel logs. Availed relay framework to implement
the interface, so Driver will just use a relay API to copy the contents
of GuC log buffer into relay's buffer.

Suggested-by: Chris Wilson <chris at chris-wilson.co.uk>
Signed-off-by: Sourab Gupta <sourab.gupta at intel.com>
Signed-off-by: Akash Goel <akash.goel at intel.com>
---
 drivers/gpu/drm/i915/i915_guc_submission.c | 125 +++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_guc.h           |   1 +
 2 files changed, 126 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
index f7f29f6..379e2843 100644
--- a/drivers/gpu/drm/i915/i915_guc_submission.c
+++ b/drivers/gpu/drm/i915/i915_guc_submission.c
@@ -23,6 +23,8 @@
  */
 #include <linux/firmware.h>
 #include <linux/circ_buf.h>
+#include <linux/debugfs.h>
+#include <linux/relay.h>
 #include "i915_drv.h"
 #include "intel_guc.h"
 
@@ -837,6 +839,124 @@ static void guc_read_update_log_buffer(struct drm_device *dev)
 	guc_move_to_next_buf(guc);
 }
 
+#ifdef CONFIG_DEBUG_FS
+/*
+ * Sub buffer switch callback. If this callback is not implemented
+ * relay will operate in non-overwrite mode so will stop accepting
+ * new data if there are no empty sub buffers left.
+ */
+static int subbuf_start_callback(struct rchan_buf *buf,
+				 void *subbuf,
+				 void *prev_subbuf,
+				 size_t prev_padding)
+{
+	/* Always switch to next sub buffer as we don't mind overwriting of
+	 * old data/logs.
+	 */
+	return 1;
+}
+
+/*
+ * file_create() callback. Creates relay file in debugfs.
+ */
+static struct dentry *create_buf_file_callback(const char *filename,
+					       struct dentry *parent,
+					       umode_t mode,
+					       struct rchan_buf *buf,
+					       int *is_global)
+{
+	/* The relay API seems to fit well with debugfs only.
+	 * There are 3 requirements to associate a file with relay channel,
+	 * a) Need the associated dentry pointer of the file while opening
+	 *    the relay channel.
+	 * b) Should use 'relay_file_operations' fops for the file.
+	 * c) The private field of file's inode should be set to the pointer
+	 *    of relay channel buffer.
+	 * All the above 3 requirements can be met for a debugfs file in a
+	 * straightforward manner, but not for a file created inside the
+	 * sysfs or for a file created as a character device file.
+	 */
+	struct dentry *buf_file = debugfs_create_file(filename, mode,
+			parent, buf, &relay_file_operations);
+
+	/* This to enable the use of a single buffer for the relay channel and
+	 * correspondingly have a single file exposed to User, through which
+	 * it can pull the logs in order without any post-processing.
+	 */
+	*is_global = 1;
+
+	return buf_file;
+}
+
+/*
+ * file_remove() default callback. Removes relay file in debugfs.
+ */
+static int remove_buf_file_callback(struct dentry *dentry)
+{
+	debugfs_remove(dentry);
+	return 0;
+}
+
+/* relay channel callbacks */
+static struct rchan_callbacks relay_callbacks = {
+	.subbuf_start = subbuf_start_callback,
+	.create_buf_file = create_buf_file_callback,
+	.remove_buf_file = remove_buf_file_callback,
+};
+
+static void guc_remove_log_relay_file(struct intel_guc *guc)
+{
+	relay_close(guc->log_relay_chan);
+}
+
+static void guc_create_log_relay_file(struct intel_guc *guc)
+{
+	struct drm_i915_private *dev_priv = guc_to_i915(guc);
+	struct drm_device *dev = dev_priv->dev;
+	struct dentry *log_dir;
+	struct rchan *guc_log_relay_chan;
+	size_t n_subbufs, subbuf_size;
+
+	/* For now create the log file in /sys/kernel/debug/dri dir. */
+	log_dir = dev->primary->debugfs_root->d_parent;
+
+	/* Keep the size of sub buffers same as shared log buffer */
+	subbuf_size = guc->log_obj->base.size;
+	/* TODO: Decide based on the User's input */
+	n_subbufs = 4;
+
+	guc_log_relay_chan = relay_open("guc_log", log_dir,
+			subbuf_size, n_subbufs, &relay_callbacks, dev);
+
+	if (!guc_log_relay_chan) {
+		DRM_ERROR("Couldn't create relay chan for guc logs\n");
+		return;
+	}
+
+	guc->log_relay_chan = guc_log_relay_chan;
+
+	/* Enable interrupt to start capturing of the logs inside the
+	 * relay channel's buffer.
+	 */
+	if (i915.guc_log_level >= 0)
+		gen8_enable_guc_interrupts(dev);
+}
+#endif
+
+static void guc_logging_fini(struct intel_guc *guc)
+{
+#ifdef CONFIG_DEBUG_FS
+        guc_remove_log_relay_file(guc);
+#endif
+}
+
+static void guc_logging_init(struct intel_guc *guc)
+{
+#ifdef CONFIG_DEBUG_FS
+	guc_create_log_relay_file(guc);
+#endif
+}
+
 static void guc_create_log(struct intel_guc *guc)
 {
 	struct drm_i915_private *dev_priv = guc_to_i915(guc);
@@ -873,6 +993,7 @@ static void guc_create_log(struct intel_guc *guc)
 
 	offset = i915_gem_obj_ggtt_offset(obj) >> PAGE_SHIFT; /* in pages */
 	guc->log_flags = (offset << GUC_LOG_BUF_ADDR_SHIFT) | flags;
+	guc_logging_init(guc);
 }
 
 static void init_guc_policies(struct guc_policies *policies)
@@ -1037,6 +1158,7 @@ void i915_guc_submission_fini(struct drm_device *dev)
 
 	gem_release_guc_obj(dev_priv->guc.log_obj);
 	guc->log_obj = NULL;
+	guc_logging_fini(guc);
 
 	if (guc->ctx_pool_obj)
 		ida_destroy(&guc->ctx_ids);
@@ -1086,6 +1208,9 @@ int intel_guc_resume(struct drm_device *dev)
 	if (guc->guc_fw.guc_fw_load_status != GUC_FIRMWARE_SUCCESS)
 		return 0;
 
+	if (i915.guc_log_level >= 0 && guc->log_relay_chan)
+		gen8_enable_guc_interrupts(dev);
+
 	ctx = dev_priv->kernel_context;
 
 	data[0] = HOST2GUC_ACTION_EXIT_S_STATE;
diff --git a/drivers/gpu/drm/i915/intel_guc.h b/drivers/gpu/drm/i915/intel_guc.h
index 92d70d8..bf61925 100644
--- a/drivers/gpu/drm/i915/intel_guc.h
+++ b/drivers/gpu/drm/i915/intel_guc.h
@@ -125,6 +125,7 @@ struct intel_guc {
 	struct intel_guc_fw guc_fw;
 	uint32_t log_flags;
 	struct drm_i915_gem_object *log_obj;
+	struct rchan *log_relay_chan;
 	/*
 	 * work, interrupts_enabled are protected by dev_priv->irq_lock
 	 */
-- 
1.9.2