Re: [Intel-gfx] [PATCH] drm/i915/display: Use dma_fence interfaces instead of i915_sw_fence

[Maarten Lankhorst <maarten.lankhorst@linux.intel.com>]

On 2023-10-18 17:38, Ville Syrjälä wrote:
> On Mon, Oct 16, 2023 at 11:08:03AM +0300, Jouni Högander wrote:
>> We are preparing for Xe driver. Xe driver doesn't have i915_sw_fence
>> implementation. Lets drop i915_sw_fence usage from display code and
>> use dma_fence interfaces directly.
>>
>> For this purpose stack dma fences from related objects into old and new
>> plane states using drm_gem_plane_helper_prepare_fb. Then wait for these
>> stacked fences during atomic commit.
>>
>> There is no be need for separate GPU reset handling in
>> intel_atomic_commit_fence_wait as the fences are signaled when GPU hang is
>> detected and GPU is being reset.
>>
>> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
>> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>> Cc: José Roberto de Souza <jose.souza@intel.com>
>>
>> Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
>> ---
>>   drivers/gpu/drm/i915/display/intel_atomic.c   |  3 -
>>   .../gpu/drm/i915/display/intel_atomic_plane.c | 49 +++---------
>>   drivers/gpu/drm/i915/display/intel_display.c  | 78 ++++++-------------
>>   .../drm/i915/display/intel_display_types.h    |  2 -
>>   4 files changed, 37 insertions(+), 95 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_atomic.c b/drivers/gpu/drm/i915/display/intel_atomic.c
>> index 5d18145da279..ec0d5168b503 100644
>> --- a/drivers/gpu/drm/i915/display/intel_atomic.c
>> +++ b/drivers/gpu/drm/i915/display/intel_atomic.c
>> @@ -331,9 +331,6 @@ void intel_atomic_state_free(struct drm_atomic_state *_state)
>>   
>>   	drm_atomic_state_default_release(&state->base);
>>   	kfree(state->global_objs);
>> -
>> -	i915_sw_fence_fini(&state->commit_ready);
>> -
>>   	kfree(state);
>>   }
>>   
>> diff --git a/drivers/gpu/drm/i915/display/intel_atomic_plane.c b/drivers/gpu/drm/i915/display/intel_atomic_plane.c
>> index b1074350616c..d4f9168ec42c 100644
>> --- a/drivers/gpu/drm/i915/display/intel_atomic_plane.c
>> +++ b/drivers/gpu/drm/i915/display/intel_atomic_plane.c
>> @@ -32,6 +32,7 @@
>>    */
>>   
>>   #include <drm/drm_atomic_helper.h>
>> +#include <drm/drm_gem_atomic_helper.h>
>>   #include <drm/drm_blend.h>
>>   #include <drm/drm_fourcc.h>
>>   
>> @@ -1035,7 +1036,7 @@ intel_prepare_plane_fb(struct drm_plane *_plane,
>>   	struct intel_atomic_state *state =
>>   		to_intel_atomic_state(new_plane_state->uapi.state);
>>   	struct drm_i915_private *dev_priv = to_i915(plane->base.dev);
>> -	const struct intel_plane_state *old_plane_state =
>> +	struct intel_plane_state *old_plane_state =
>>   		intel_atomic_get_old_plane_state(state, plane);
>>   	struct drm_i915_gem_object *obj = intel_fb_obj(new_plane_state->hw.fb);
>>   	struct drm_i915_gem_object *old_obj = intel_fb_obj(old_plane_state->hw.fb);
>> @@ -1057,56 +1058,30 @@ intel_prepare_plane_fb(struct drm_plane *_plane,
>>   		 * This should only fail upon a hung GPU, in which case we
>>   		 * can safely continue.
>>   		 */
>> -		if (new_crtc_state && intel_crtc_needs_modeset(new_crtc_state)) {
>> -			ret = i915_sw_fence_await_reservation(&state->commit_ready,
>> -							      old_obj->base.resv,
>> -							      false, 0,
>> -							      GFP_KERNEL);
>> +		if (new_crtc_state && intel_crtc_needs_modeset(new_crtc_state) &&
>> +		    !dma_resv_test_signaled(old_obj->base.resv,
>> +					    dma_resv_usage_rw(false))) {
>> +			ret = drm_gem_plane_helper_prepare_fb(_plane, &old_plane_state->uapi);
> 
> This I think is broken. The old plane state and its fence can still be
> in use by the previous commit, so we cannot mutate it here. Thus we
> really need to get the implicit fence from the old fb chained into the
> new plane state's fence.
Is it even needed though? If new_plane_state always calls prepare_fb.

Cheers,
~Maarten