[Intel-gfx] [PATCH v3] drm/i915: Use trace_printk to provide a death rattle for GEM

[Chris Wilson]

Quoting Chris Wilson (2017-11-09 14:30:19)
> Trying to enable printk debugging for GEM is fraught with the issue of
> spam; interactions with HW are very frequent and often boring. However,
> one instance where they are not so boring is just before a BUG; here
> ftrace provides a facility to dump its ringbuffer on an oops. So for CI
> let's enable trace_printk() to capture the last exchanges with HW as a
> death rattle.

Something worth mentioning is that using trace_printk, generates

[    5.112689] **********************************************************
[    5.112693] **   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **
[    5.112698] **                                                      **
[    5.112701] ** trace_printk() being used. Allocating extra memory.  **
[    5.112705] **                                                      **
[    5.112709] ** This means that this is a DEBUG kernel and it is     **
[    5.112713] ** unsafe for production use.                           **
[    5.112716] **                                                      **
[    5.112720] ** If you see this message and you are not debugging    **
[    5.112724] ** the kernel, report this immediately to your vendor!  **
[    5.112728] **                                                      **
[    5.112732] **   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **
[    5.112735] **********************************************************

Hiding it behind a CI Kconfig option is essential.
-Chris