Re: [PATCH v3 1/6] drm/komeda: Add side by side assembling

["james qian wang (Arm Technology China)" <james.qian.wang@arm.com>]

On Fri, Nov 15, 2019 at 12:02:00AM +0000, Mihail Atanassov wrote:
> Hi James,
> 
> On Thursday, 14 November 2019 08:37:24 GMT james qian wang (Arm Technology China) wrote:
> > Komeda HW can support side by side, which splits the internal display
> > processing to two single halves (LEFT/RIGHT) and handle them by two
> > pipelines separately.
> > komeda "side by side" is enabled by DT property: "side_by_side_master",
> > once DT configured side by side, komeda need to verify it with HW's
> > configuration, and assemble it for the further usage.
> 
> A few problems I see with this approach:
>  - This property doesn't scale to >2 pipes;
>  - Our HW is capable of dynamically switching between SBS and non-SBS
> modes, with this DT property you're effectively denying the opportunity
> to use the second pipe when the first one can be satisfied with
> 4 planes and 1px/clk.
> 
> If we only want to fix the first problem, then at least we need this
> to be a property of the pipeline node with a phandle linking slave to
> master (or bidirectional).

I had consider this way before, but consider we have no product (now
and in next 2/3 years) can support >2 pipes. So for DT I decide to
focus on current, but you may see I add two side_by_side flags.

  - mdev->side_by_side.
  - crtc->side_by_side.

And beside the DT parse we use mdev->side_by_side, the real SBS
operation actually based on crtc->side_by_side, then once the HW
changed, we only need to update the SBS assemble/decision code, but no
need to update the real sbs logic.

thanks
James

> For the second, why not do the SBS decision at modeset time?
> If the first CRTC has dual-link output and the commit:
>  - only drives one CRTC
>  - uses up to 4 planes
>  - doesn't meet clk requirements without SBS but does with SBS
> then we can switch SBS on dynamically.
> And we can tweak that decision with power use in mind later on since
> there's no user-visible knob.

Yes, you're right, current implementation just use simplest way to
show the feature, and for dynamic enable/disable sbs will be added
when we have the real usage case.

> We can still keep a DT property if we have a use case for it (e.g.
> forcing SBS on for some reason), but we might want to name it slightly
> more conservatively then, so it doesn't imply that we never do SBS
> when it's not there.
> 
> Lastly, maintaining that property in combination with the dynamic
> modeset-time SBS decision tree means extra code for more or less the
> same functionality. <2c>I'm not 100% sure it's worth it.</2c>

I think we'd add such support when we have the real use case. :)

> > 
> > v3: Correct a typo.
> > 
> > Signed-off-by: James Qian Wang (Arm Technology China) <james.qian.wang@arm.com>
> > ---
> >  .../gpu/drm/arm/display/komeda/komeda_crtc.c  | 13 ++++-
> >  .../gpu/drm/arm/display/komeda/komeda_dev.c   |  3 ++
> >  .../gpu/drm/arm/display/komeda/komeda_dev.h   |  9 ++++
> >  .../gpu/drm/arm/display/komeda/komeda_kms.h   |  3 ++
> >  .../drm/arm/display/komeda/komeda_pipeline.c  | 50 +++++++++++++++++--
> >  .../drm/arm/display/komeda/komeda_pipeline.h  |  1 +
> >  6 files changed, 73 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c b/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
> > index 1c452ea75999..cee9a1692e71 100644
> > --- a/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
> > +++ b/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
> > @@ -561,21 +561,30 @@ int komeda_kms_setup_crtcs(struct komeda_kms_dev *kms,
> >  	kms->n_crtcs = 0;
> >  
> >  	for (i = 0; i < mdev->n_pipelines; i++) {
> > +		/* if sbs, one komeda_dev only can represent one CRTC */
> > +		if (mdev->side_by_side && i != mdev->side_by_side_master)
> > +			continue;
> > +
> >  		crtc = &kms->crtcs[kms->n_crtcs];
> >  		master = mdev->pipelines[i];
> >  
> >  		crtc->master = master;
> >  		crtc->slave  = komeda_pipeline_get_slave(master);
> > +		crtc->side_by_side = mdev->side_by_side;
> >  
> >  		if (crtc->slave)
> >  			sprintf(str, "pipe-%d", crtc->slave->id);
> >  		else
> >  			sprintf(str, "None");
> >  
> > -		DRM_INFO("CRTC-%d: master(pipe-%d) slave(%s).\n",
> > -			 kms->n_crtcs, master->id, str);
> > +		DRM_INFO("CRTC-%d: master(pipe-%d) slave(%s) sbs(%s).\n",
> > +			 kms->n_crtcs, master->id, str,
> > +			 crtc->side_by_side ? "On" : "Off");
> >  
> >  		kms->n_crtcs++;
> > +
> > +		if (mdev->side_by_side)
> > +			break;
> >  	}
> >  
> >  	return 0;
> > diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_dev.c b/drivers/gpu/drm/arm/display/komeda/komeda_dev.c
> > index 4e46f650fddf..c3fa4835cb8d 100644
> > --- a/drivers/gpu/drm/arm/display/komeda/komeda_dev.c
> > +++ b/drivers/gpu/drm/arm/display/komeda/komeda_dev.c
> > @@ -178,6 +178,9 @@ static int komeda_parse_dt(struct device *dev, struct komeda_dev *mdev)
> >  		}
> >  	}
> >  
> > +	mdev->side_by_side = !of_property_read_u32(np, "side_by_side_master",
> > +						   &mdev->side_by_side_master);
> > +
> >  	return ret;
> >  }
> >  
> > diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_dev.h b/drivers/gpu/drm/arm/display/komeda/komeda_dev.h
> > index d406a4d83352..471604b42431 100644
> > --- a/drivers/gpu/drm/arm/display/komeda/komeda_dev.h
> > +++ b/drivers/gpu/drm/arm/display/komeda/komeda_dev.h
> > @@ -183,6 +183,15 @@ struct komeda_dev {
> >  
> >  	/** @irq: irq number */
> >  	int irq;
> > +	/**
> > +	 * @side_by_side:
> > +	 *
> > +	 * on sbs the whole display frame will be split to two halves (1:2),
> > +	 * master pipeline handles the left part, slave for the right part
> > +	 */
> > +	bool side_by_side;
> 
> That's a duplicate of the one in komeda_crtc. You don't need both.
> 
> > +	/** @side_by_side_master: master pipe id for side by side */
> > +	int side_by_side_master;
> 
> As I detailed above, this should be on the crtc, otherwise we can't
> scale to >2 pipes.
> 
> >  
> >  	/** @lock: used to protect dpmode */
> >  	struct mutex lock;
> > diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_kms.h b/drivers/gpu/drm/arm/display/komeda/komeda_kms.h
> > index 456f3c435719..ae6654fe95e2 100644
> > --- a/drivers/gpu/drm/arm/display/komeda/komeda_kms.h
> > +++ b/drivers/gpu/drm/arm/display/komeda/komeda_kms.h
> > @@ -76,6 +76,9 @@ struct komeda_crtc {
> >  	 */
> >  	struct komeda_pipeline *slave;
> >  
> > +	/** @side_by_side: if the master and slave works on side by side mode */
> > +	bool side_by_side;
> > +
> >  	/** @slave_planes: komeda slave planes mask */
> >  	u32 slave_planes;
> >  
> > diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_pipeline.c b/drivers/gpu/drm/arm/display/komeda/komeda_pipeline.c
> > index 452e505a1fd3..104e27cc1dc3 100644
> > --- a/drivers/gpu/drm/arm/display/komeda/komeda_pipeline.c
> > +++ b/drivers/gpu/drm/arm/display/komeda/komeda_pipeline.c
> > @@ -326,14 +326,56 @@ static void komeda_pipeline_assemble(struct komeda_pipeline *pipe)
> >  struct komeda_pipeline *
> >  komeda_pipeline_get_slave(struct komeda_pipeline *master)
> >  {
> > -	struct komeda_component *slave;
> > +	struct komeda_dev *mdev = master->mdev;
> > +	struct komeda_component *comp, *slave;
> > +	u32 avail_inputs;
> > +
> > +	/* on SBS, slave pipeline merge to master via image processor */
> > +	if (mdev->side_by_side) {
> > +		comp = &master->improc->base;
> > +		avail_inputs = KOMEDA_PIPELINE_IMPROCS;
> > +	} else {
> > +		comp = &master->compiz->base;
> > +		avail_inputs = KOMEDA_PIPELINE_COMPIZS;
> > +	}
> >  
> > -	slave = komeda_component_pickup_input(&master->compiz->base,
> > -					      KOMEDA_PIPELINE_COMPIZS);
> > +	slave = komeda_component_pickup_input(comp, avail_inputs);
> >  
> >  	return slave ? slave->pipeline : NULL;
> >  }
> >  
> > +static int komeda_assemble_side_by_side(struct komeda_dev *mdev)
> > +{
> > +	struct komeda_pipeline *master, *slave;
> > +	int i;
> > +
> > +	if (!mdev->side_by_side)
> > +		return 0;
> > +
> > +	if (mdev->side_by_side_master >= mdev->n_pipelines) {
> > +		DRM_ERROR("DT configured side by side master-%d is invalid.\n",
> > +			  mdev->side_by_side_master);
> > +		return -EINVAL;
> > +	}
> > +
> > +	master = mdev->pipelines[mdev->side_by_side_master];
> > +	slave = komeda_pipeline_get_slave(master);
> > +	if (!slave || slave->n_layers != master->n_layers) {
> > +		DRM_ERROR("Current HW doesn't support side by side.\n");
> > +		return -EINVAL;
> > +	}
> > +
> > +	if (!master->dual_link) {
> > +		DRM_DEBUG_ATOMIC("SBS can not work without dual link.\n");
> > +		return -EINVAL;
> > +	}
> > +
> > +	for (i = 0; i < master->n_layers; i++)
> > +		master->layers[i]->sbs_slave = slave->layers[i];
> > +
> > +	return 0;
> > +}
> > +
> >  int komeda_assemble_pipelines(struct komeda_dev *mdev)
> >  {
> >  	struct komeda_pipeline *pipe;
> > @@ -346,7 +388,7 @@ int komeda_assemble_pipelines(struct komeda_dev *mdev)
> >  		komeda_pipeline_dump(pipe);
> >  	}
> >  
> > -	return 0;
> > +	return komeda_assemble_side_by_side(mdev);
> >  }
> >  
> >  void komeda_pipeline_dump_register(struct komeda_pipeline *pipe,
> > diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_pipeline.h b/drivers/gpu/drm/arm/display/komeda/komeda_pipeline.h
> > index ac8725e24853..20a076cce635 100644
> > --- a/drivers/gpu/drm/arm/display/komeda/komeda_pipeline.h
> > +++ b/drivers/gpu/drm/arm/display/komeda/komeda_pipeline.h
> > @@ -237,6 +237,7 @@ struct komeda_layer {
> >  	 * not the source buffer.
> >  	 */
> >  	struct komeda_layer *right;
> > +	struct komeda_layer *sbs_slave;
> >  };
> >  
> >  struct komeda_layer_state {
> > 
> 
> 
> -- 
> Mihail
> 
>