Re: [Intel-gfx] [PATCH] drm/i915/tgl: Put HDC flush pipe_control bit in the right dword

[Kenneth Graunke <kenneth@whitecape.org>]

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On Monday, May 4, 2020 5:01:46 PM PDT D Scott Phillips wrote:
> Previously we set HDC_PIPELINE_FLUSH in dword 1 of gen12
> pipe_control commands. HDC Pipeline flush actually resides in
> dword 0, and the bit we were setting in dword 1 was Indirect State
> Pointers Disable, which invalidates indirect state in the render
> context. This causes failures for userspace, as things like push
> constant state gets invalidated.
> 
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Signed-off-by: D Scott Phillips <d.scott.phillips@intel.com>
> ---
>  drivers/gpu/drm/i915/gt/intel_engine.h | 23 +++++++++++++++++------
>  drivers/gpu/drm/i915/gt/intel_lrc.c    | 11 ++++++-----
>  2 files changed, 23 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine.h b/drivers/gpu/drm/i915/gt/intel_engine.h
> index 19d0b8830905..8338be338ec8 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine.h
> +++ b/drivers/gpu/drm/i915/gt/intel_engine.h
> @@ -241,19 +241,24 @@ void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine);
>  void intel_engine_print_breadcrumbs(struct intel_engine_cs *engine,
>  				    struct drm_printer *p);
>  
> -static inline u32 *gen8_emit_pipe_control(u32 *batch, u32 flags, u32 offset)
> +static inline u32 *gen12_emit_pipe_control(u32 *batch, u32 flags0, u32 flags1, u32 offset)

Great find!  It looks like HDC_PIPELINE_FLUSH moved from bit 41 to bit 9
even on Icelake / Gen11 - so it might make sense to call this
gen11_emit_pipe_control() and use it on the Icelake functions.

That said, i915 never sets HDC_PIPELINE_FLUSH until Gen12, so we don't
actually have a bug to fix on Icelake today.  But if someone started
trying to set it on Gen11, we would have a bug - hence the suggestion.

With or without any changes,

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

and thanks so much for tracking this down!

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