Re: [PATCH 20/20] drm/i915: Early creation of relay channel for capturing boot time logs

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 12/08/16 17:31, Goel, Akash wrote:
> On 8/12/2016 9:52 PM, Tvrtko Ursulin wrote:
>> On 12/08/16 07:25, akash.goel@intel.com wrote:
>>> From: Akash Goel <akash.goel@intel.com>
>>>
>>> As per the current i915 Driver load sequence, debugfs registration is
>>> done
>>> at the end and so the relay channel debugfs file is also created after
>>> that
>>> but the GuC firmware is loaded much earlier in the sequence.
>>> As a result Driver could miss capturing the boot-time logs of GuC
>>> firmware
>>> if there are flush interrupts from the GuC side.
>>> Relay has a provision to support early logging where initially only
>>> relay
>>> channel can be created, to have buffers for storing logs, and later on
>>> channel can be associated with a debugfs file at appropriate time.
>>> Have availed that, which allows Driver to capture boot time logs also,
>>> which can be collected once Userspace comes up.
>>>
>>> Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
>>> Signed-off-by: Akash Goel <akash.goel@intel.com>
>>> ---
>>>   drivers/gpu/drm/i915/i915_guc_submission.c | 61
>>> +++++++++++++++++++++---------
>>>   1 file changed, 44 insertions(+), 17 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c
>>> b/drivers/gpu/drm/i915/i915_guc_submission.c
>>> index af48f62..1c287d7 100644
>>> --- a/drivers/gpu/drm/i915/i915_guc_submission.c
>>> +++ b/drivers/gpu/drm/i915/i915_guc_submission.c
>>> @@ -1099,25 +1099,12 @@ static void guc_remove_log_relay_file(struct
>>> intel_guc *guc)
>>>       relay_close(guc->log.relay_chan);
>>>   }
>>>
>>> -static int guc_create_log_relay_file(struct intel_guc *guc)
>>> +static int guc_create_relay_channel(struct intel_guc *guc)
>>>   {
>>>       struct drm_i915_private *dev_priv = guc_to_i915(guc);
>>>       struct rchan *guc_log_relay_chan;
>>> -    struct dentry *log_dir;
>>>       size_t n_subbufs, subbuf_size;
>>>
>>> -    /* For now create the log file in /sys/kernel/debug/dri/0 dir */
>>> -    log_dir = dev_priv->drm.primary->debugfs_root;
>>> -
>>> -    /* 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.
>>
>> It only needs a dentry, I don't see that it has to be a debugfs one.
>>
> Besides dentry, there are other requirements for using relay, which can
> be met only for a debugfs file.
> debugfs wasn't the preferred choice to place the log file, but had no
> other option, as relay API is compatible with debugfs only.

What are those and should they be mentioned in the comment above?

Regards,

Tvrtko
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