[PATCH 06/11] drm/i915: Add a relay backed debugfs interface for capturing GuC logs

akash.goel
2016-06-27T12:04:12Z

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

Added a new debugfs interface '/sys/kernel/debug/dri/guc_log' for the
User to capture GuC firmware logs. Availed relay framework to implement
the interface, where Driver will have to just use a relay API to store
snapshots of the GuC log buffer in the buffer managed by relay.
The snapshot will be taken when GuC firmware sends a log buffer flush
interrupt and up to four snaphots could be stored in the relay buffer.
The relay buffer will be operated in a mode where it will overwrite the
data not yet collected by User.
Besides mmap method, through which User can directly access the relay
buffer contents, relay also supports the 'poll' method. Through the 'poll'
call on log file, User can come to know whenever a new snapshot of the
log buffer is taken by Driver, so can run in tandem with the Driver and
capture the logs in a sustained/streaming manner, without any loss of data.

Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Sourab Gupta <sourab.gupta@intel.com>
Signed-off-by: Akash Goel <akash.goel@intel.com>
---
drivers/gpu/drm/i915/i915_guc_submission.c | 133 ++++++++++++++++++++++++++++-
drivers/gpu/drm/i915/intel_guc.h | 1 +
2 files changed, 133 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
index b95a510..45f3396 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"

@@ -821,7 +823,15 @@ err:

static void* guc_get_write_buffer(struct intel_guc *guc)
{
- return NULL;
+ if (!guc->log_relay_chan)
+ return NULL;
+
+ /* Get the pointer to relay sub buffer and copy data into it ourselves.
+ * Could have used the relay_write() to indirectly copy the data, but
+ * that would have been bit convoluted, as we also need to update the
+ * first page containing state data.
+ */
+ return relay_reserve(guc->log_relay_chan, guc->log_obj->base.size);
}

static void guc_read_update_log_buffer(struct drm_device *dev)
@@ -878,6 +888,125 @@ static void guc_read_update_log_buffer(struct drm_device *dev)
}
}

+/*
+ * 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)
+{
+ /*
+ * Not using the channel filename passed as an argument, since for each
+ * channel relay appends the corresponding CPU number to the filename
+ * passed in relay_open(). This should be fine as relay just needs a
+ * dentry of the file associated with the channel buffer and that file's
+ * name need not be same as the filename passed as an argument.
+ */
+ struct dentry *buf_file = debugfs_create_file("guc_log", 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;
+
+ if (guc->log_relay_chan)
+ return;
+
+ /* If /sys/kernel/debug/dri/0 location do not exist, then debugfs is
+ * not mounted and so can't create the relay file.
+ * The relay API seems to fit well with debugfs only.
+ */
+ if (!dev->primary->debugfs_root) {
+ /* logging will remain off */
+ i915.guc_log_level = -1;
+ return;
+ }
+
+ /* 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");
+ /* keep logging off as couldn't create the relay channel in
+ * in which the logs can be stored.
+ */
+ i915.guc_log_level = -1;
+ return;
+ }
+
+ guc->log_relay_chan = guc_log_relay_chan;
+}
+
+static void guc_logging_fini(struct intel_guc *guc)
+{
+ guc_remove_log_relay_file(guc);
+}
+
+static void guc_logging_init(struct intel_guc *guc)
+{
+ guc_create_log_relay_file(guc);
+}
+
static void guc_create_log(struct intel_guc *guc)
{
struct drm_i915_private *dev_priv = guc_to_i915(guc);
@@ -914,6 +1043,7 @@ 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)
@@ -1074,6 +1204,7 @@ void i915_guc_submission_fini(struct drm_i915_private *dev_priv)
gem_release_guc_obj(dev_priv->guc.ads_obj);
guc->ads_obj = NULL;

+ guc_logging_fini(guc);
gem_release_guc_obj(dev_priv->guc.log_obj);
guc->log_obj = NULL;

diff --git a/drivers/gpu/drm/i915/intel_guc.h b/drivers/gpu/drm/i915/intel_guc.h
index b20e167..c675856 100644
--- a/drivers/gpu/drm/i915/intel_guc.h
+++ b/drivers/gpu/drm/i915/intel_guc.h
@@ -126,6 +126,7 @@ 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