Re: [Intel-gfx] [RFC 0/2] drm/connector: connector iterator with filtering

[Harry Wentland <harry.wentland@amd.com>]

On 10/5/22 06:51, Jani Nikula wrote:
> Currently i915 assumes all drm_connectors it encounters are embedded in
> intel_connectors that i915 allocated. The drm_writeback_connector forces
> a design where this is not the case; we can't provide our own connector,
> and writeback embeds the drm_connector it initializes itself.
> 
> To use drm writeback, none of the i915 connector iteration could assume
> the drm connector is embedded in intel_connector. Checking this is
> tedious, and would require an intermediate step with
> drm_connector. Here's an idea I came up with; filtering at the drm
> connector iterator level with a caller supplied function. Not too much
> code, and could be used for other things as well.
> 

We've been trying to hook up drm_writeback_connector in amdgpu and
this would be really helpful. I've had to do liberal sprinkling
of "!= DRM_MODE_CONNECTOR_WRITEBACK" all over the place.

> Mind you, we'd still much rather modify drm writeback to allow passing
> the connector i915 allocated, instead of the current midlayer design
> that forces drivers to a certain model. Working around this is a bunch
> of error prone and tedious code that we really could do without.
> 

I think this would be even better but also be much more work and impact
every driver that implements writeback. FWIW, there was no way for me
to add writeback connector handling without KASAN. Interpreting the
connector wrong in one place leads to memory corruption and
undefined behavior and is almost impossible to spot without KASAN.

This series is
Acked-by: Harry Wentland <harry.wentland@amd.com>

Harry

> 
> BR,
> Jani.
> 
> 
> Cc: Arun R Murthy <arun.r.murthy@intel.com>
> Cc: Dave Airlie <airlied@gmail.com>
> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Cc: Suraj Kandpal <suraj.kandpal@intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> Jani Nikula (2):
>   drm/connector: add connector list iteration with filtering
>   drm/i915: iterate intel_connectors only
> 
>  drivers/gpu/drm/drm_connector.c               | 57 +++++++++++++++----
>  drivers/gpu/drm/i915/display/intel_display.c  |  3 +-
>  .../drm/i915/display/intel_display_types.h    |  7 +++
>  drivers/gpu/drm/i915/display/intel_dp.c       |  6 +-
>  drivers/gpu/drm/i915/display/intel_dp_mst.c   |  3 +-
>  drivers/gpu/drm/i915/display/intel_hdcp.c     |  3 +-
>  drivers/gpu/drm/i915/display/intel_hotplug.c  | 12 ++--
>  .../drm/i915/display/intel_modeset_setup.c    |  6 +-
>  drivers/gpu/drm/i915/display/intel_opregion.c |  9 ++-
>  include/drm/drm_connector.h                   |  9 +++
>  10 files changed, 89 insertions(+), 26 deletions(-)
>