Re: [PATCH 07/17] drm/i915: Add a relay backed debugfs interface for capturing GuC logs

["Goel, Akash" <akash.goel@intel.com>]

On 7/19/2016 5:01 PM, Tvrtko Ursulin wrote:
>
> On 10/07/16 14:41, akash.goel@intel.com wrote:
>> 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.
>>
>> v2: Defer the creation of relay channel & associated debugfs file, as
>>      debugfs setup is now done at the end of i915 Driver load. (Chris)
>>
>> v3:
>> - Switch to no-overwrite mode for relay.
>> - Fix the relay sub buffer switching sequence.
>>
>> 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_drv.c            |   2 +
>>   drivers/gpu/drm/i915/i915_guc_submission.c | 197
>> ++++++++++++++++++++++++++++-
>>   drivers/gpu/drm/i915/intel_guc.h           |   3 +
>>   3 files changed, 199 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_drv.c
>> b/drivers/gpu/drm/i915/i915_drv.c
>> index 25c6b9b..43c9900 100644
>> --- a/drivers/gpu/drm/i915/i915_drv.c
>> +++ b/drivers/gpu/drm/i915/i915_drv.c
>> @@ -1177,6 +1177,7 @@ static void i915_driver_register(struct
>> drm_i915_private *dev_priv)
>>       /* Reveal our presence to userspace */
>>       if (drm_dev_register(dev, 0) == 0) {
>>           i915_debugfs_register(dev_priv);
>> +        i915_guc_register(dev);
>>           i915_setup_sysfs(dev);
>>       } else
>>           DRM_ERROR("Failed to register driver for userspace access!\n");
>> @@ -1215,6 +1216,7 @@ static void i915_driver_unregister(struct
>> drm_i915_private *dev_priv)
>>       intel_opregion_unregister(dev_priv);
>>
>>       i915_teardown_sysfs(&dev_priv->drm);
>> +    i915_guc_unregister(&dev_priv->drm);
>>       i915_debugfs_unregister(dev_priv);
>>       drm_dev_unregister(&dev_priv->drm);
>>
>> diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c
>> b/drivers/gpu/drm/i915/i915_guc_submission.c
>> index d3dbb8e..9b436fa 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"
>>
>> @@ -836,12 +838,33 @@ err:
>>
>>   static void guc_move_to_next_buf(struct intel_guc *guc)
>>   {
>> -    return;
>> +    /* Make sure our updates are in the sub buffer are visible when
>> +     * Consumer sees a newly produced sub buffer.
>> +     */
>> +    smp_wmb();
>> +
>> +    /* All data has been written, so now move the offset of sub
>> buffer. */
>> +    relay_reserve(guc->log.relay_chan, guc->log.obj->base.size);
>> +
>> +    /* Switch to the next sub buffer */
>> +    relay_flush(guc->log.relay_chan);
>>   }
>>
>>   static void* guc_get_write_buffer(struct intel_guc *guc)
>>   {
>> -    return NULL;
>> +    /* FIXME: Cover the check under a lock ? */
>> +    if (!guc->log.relay_chan)
>> +        return NULL;
>> +
>> +    /* Just get the base address of a new sub buffer and copy data
>> into it
>> +     * ourselves. NULL will be returned in no-overwrite mode, if all sub
>> +     * buffers are full. Could have used the relay_write() to indirectly
>> +     * copy the data, but that would have been bit convoluted, as we
>> need to
>> +     * write to only certain locations inside a sub buffer which
>> cannot be
>> +     * done without using relay_reserve() along with relay_write().
>> So its
>> +     * better to use relay_reserve() alone.
>> +     */
>> +    return relay_reserve(guc->log.relay_chan, 0);
>>   }
>>
>>   static void guc_read_update_log_buffer(struct drm_device *dev)
>> @@ -906,6 +929,119 @@ static void guc_read_update_log_buffer(struct
>> drm_device *dev)
>>           guc_move_to_next_buf(guc);
>>   }
>>
>> +/*
>> + * Sub buffer switch callback. Called whenever relay has to switch to
>> a new
>> + * sub buffer, relay stays on the same sub buffer if 0 is returned.
>> + */
>> +static int subbuf_start_callback(struct rchan_buf *buf,
>> +                 void *subbuf,
>> +                 void *prev_subbuf,
>> +                 size_t prev_padding)
>> +{
>> +    /* Use no-overwrite mode by default, where relay will stop accepting
>> +     * new data if there are no empty sub buffers left.
>> +     * There is no strict synchronization enforced by relay between
>> Consumer
>> +     * and Producer. In overwrite mode, there is a possibility of
>> getting
>> +     * inconsistent/garbled data, the producer could be writing on to
>> the
>> +     * same sub buffer from which Consumer is reading. This can't be
>> avoided
>> +     * unless Consumer is fast enough and can always run in tandem with
>> +     * Producer.
>> +     */
>> +    if (relay_buf_full(buf))
>> +        return 0;
>> +
>> +    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 collect the logs inorder 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)
>> +{
>> +    if (guc->log.relay_chan)
>> +        relay_close(guc->log.relay_chan);
>> +}
>> +
>> +static int 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->drm;
>> +    struct dentry *log_dir;
>> +    struct rchan *guc_log_relay_chan;
>> +    size_t n_subbufs, subbuf_size;
>> +
>> +    if (guc->log.relay_chan)
>> +        return 0;
>> +
>> +    /* 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)
>> +        return -ENODEV;
>> +
>> +    /* For now create the log file in /sys/kernel/debug/dri/0 dir */
>> +    log_dir = dev->primary->debugfs_root;
>> +
>> +    /* 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_DEBUG_DRIVER("Couldn't create relay chan for guc logs\n");
>> +        return -ENOMEM;
>> +    }
>> +
>> +    /* FIXME: Cover the update under a lock ? */
>> +    guc->log.relay_chan = guc_log_relay_chan;
>> +    return 0;
>> +}
>> +
>>   static void guc_log_cleanup(struct drm_i915_private *dev_priv)
>>   {
>>       struct intel_guc *guc = &dev_priv->guc;
>> @@ -918,6 +1054,9 @@ static void guc_log_cleanup(struct
>> drm_i915_private *dev_priv)
>>       /* First disable the flush interrupt */
>>       gen9_disable_guc_interrupts(dev_priv);
>>
>> +    guc_remove_log_relay_file(guc);
>> +    guc->log.relay_chan = NULL;
>> +
>>       if (guc->log.buf_addr)
>>           i915_gem_object_unpin_map(guc->log.obj);
>>
>> @@ -996,6 +1135,39 @@ static void guc_create_log(struct intel_guc *guc)
>>       guc->log.flags = (offset << GUC_LOG_BUF_ADDR_SHIFT) | flags;
>>   }
>>
>> +static int guc_log_late_setup(struct drm_device *dev)
>> +{
>> +    struct drm_i915_private *dev_priv = dev->dev_private;
>> +    struct intel_guc *guc = &dev_priv->guc;
>> +    int ret;
>> +
>> +    lockdep_assert_held(&dev->struct_mutex);
>> +
>> +    if (i915.guc_log_level < 0)
>> +        return -EINVAL;
>> +
>> +    if (WARN_ON(guc->log.relay_chan))
>> +        return -EINVAL;
>> +
>> +    /* If log_level was set as -1 at boot time, then vmalloc mapping
>> would
>> +     * not have been created for the log buffer, so create one now.
>> +     */
>> +    ret = guc_create_log_extras(guc);
>> +    if (ret)
>> +        goto err;
>> +
>> +    ret = guc_create_log_relay_file(guc);
>> +    if (ret)
>> +        goto err;
>> +
>> +    return 0;
>> +err:
>> +    guc_log_cleanup(dev_priv);
>> +    /* logging will remain off */
>> +    i915.guc_log_level = -1;
>> +    return ret;
>> +}
>> +
>>   static void init_guc_policies(struct guc_policies *policies)
>>   {
>>       struct guc_policy *policy;
>> @@ -1154,7 +1326,6 @@ 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_log_cleanup(dev_priv);
>>       gem_release_guc_obj(dev_priv->guc.log.obj);
>>       guc->log.obj = NULL;
>>
>> @@ -1232,3 +1403,23 @@ void i915_guc_capture_logs(struct drm_device *dev)
>>       host2guc_logbuffer_flush_complete(&dev_priv->guc);
>>       intel_runtime_pm_put(dev_priv);
>>   }
>> +
>> +void i915_guc_unregister(struct drm_device *dev)
>> +{
>> +    if (!i915.enable_guc_submission)
>> +        return;
>> +
>> +    mutex_lock(&dev->struct_mutex);
>> +    guc_log_cleanup(dev->dev_private);
>> +    mutex_unlock(&dev->struct_mutex);
>> +}
>> +
>> +void i915_guc_register(struct drm_device *dev)
>> +{
>> +    if (!i915.enable_guc_submission)
>> +        return;
>> +
>> +    mutex_lock(&dev->struct_mutex);
>> +    guc_log_late_setup(dev);
>> +    mutex_unlock(&dev->struct_mutex);
>> +}
>> diff --git a/drivers/gpu/drm/i915/intel_guc.h
>> b/drivers/gpu/drm/i915/intel_guc.h
>> index d4f0fae..a784cf8 100644
>> --- a/drivers/gpu/drm/i915/intel_guc.h
>> +++ b/drivers/gpu/drm/i915/intel_guc.h
>> @@ -127,6 +127,7 @@ struct intel_guc_log {
>>       struct drm_i915_gem_object *obj;
>>       struct workqueue_struct *wq;
>>       void *buf_addr;
>> +    struct rchan *relay_chan;
>>   };
>>
>>   struct intel_guc {
>> @@ -174,5 +175,7 @@ int i915_guc_submit(struct drm_i915_gem_request *rq);
>>   void i915_guc_submission_disable(struct drm_i915_private *dev_priv);
>>   void i915_guc_submission_fini(struct drm_i915_private *dev_priv);
>>   void i915_guc_capture_logs(struct drm_device *dev);
>> +void i915_guc_register(struct drm_device *dev);
>> +void i915_guc_unregister(struct drm_device *dev);
>>
>>   #endif
>>
>
> I am clueless about relayfs - do we have someone in house who could
> provide a better review of that?
>
Probably a skim through 
https://www.kernel.org/doc/Documentation/filesystems/relay.txt & a bit 
of code walk-through would help, that's what I also had to do.

> In the mean time, you got TODO and FIXME's in the code so that needs to
> be resolved before a full review anyway. :)
>
TODO is already taken care in a subsequent patch.
About FIXME, I am not really sure and need suggestion/inputs on it.

Best regards
Akash

> Regards,
>
> Tvrtko
>
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