[PATCH v2 0/3] drm/vc4: Add a load tracker

[Paul Kocialkowski]

Hi,

On Thu, 2018-10-25 at 14:45 +0200, Boris Brezillon wrote:
> Hello,
> 
> This is the 2nd version of the VC4 load tracker patch.
> 
> Daniel, as you suggested, I've implemented a generic infrastructure to
> track and report underrun errors (patch 1). Not sure this is what you
> had in mind, but it seems to do the job for my use case, and should
> allow me to easily track regressions in the load tracking logic with a
> bunch of IGT tests. Let me know if you want it done differently.
> 
> Patch 2 is implementing the generic underrun interface in the VC4
> driver, and patch 3 is just adding the load tracking logic (hasn't
> changed since the RFC except for the unused 'ret' var removal).

For the whole series:
Tested-by: Paul Kocialkowski <paul.kocialkowski at bootlin.com>

I am currently integrating this with IGT testing and have a few general
remarks:

- I think it would make sense to have a driver-specific debugfs entry
for enabling/disabling the rejection of commits by the load tracker.
This would be useful for testing that there is no mismatch between the
load tracker's behavior and hardware-detected underruns.

- Underrun reporting with a generic debugfs entry is a good fit for IGT
(and userspace reporting in general), but it would be useful to have an
intermediary state reported between applying a commit and getting the
underrun status.

Something like returning '?' between setting a commit and the next
vblank. This way, there is no chance that userspace reads the underrun
status related to the previous configuration.

What do you think?

Cheers,

Paul

> Regards,
> 
> Boris
> 
> Boris Brezillon (3):
>   drm/atomic: Add a generic infrastructure to track underrun errors
>   drm/vc4: Report underrun errors
>   drm/vc4: Add a load tracker to prevent HVS underflow errors
> 
>  drivers/gpu/drm/drm_atomic.c        |  12 +++
>  drivers/gpu/drm/drm_atomic_helper.c |   4 +
>  drivers/gpu/drm/vc4/vc4_drv.c       |   1 +
>  drivers/gpu/drm/vc4/vc4_drv.h       |  14 ++++
>  drivers/gpu/drm/vc4/vc4_hvs.c       |  71 ++++++++++++++++++
>  drivers/gpu/drm/vc4/vc4_kms.c       | 110 +++++++++++++++++++++++++++-
>  drivers/gpu/drm/vc4/vc4_plane.c     |  60 +++++++++++++++
>  drivers/gpu/drm/vc4/vc4_regs.h      |  46 +++---------
>  include/drm/drm_atomic_helper.h     |  53 ++++++++++++++
>  include/drm/drm_device.h            |  15 ++++
>  include/drm/drm_mode_config.h       |  26 +++++++
>  11 files changed, 376 insertions(+), 36 deletions(-)
> 
-- 
Paul Kocialkowski, Bootlin (formerly Free Electrons)
Embedded Linux and kernel engineering
https://bootlin.com
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