Re: [RESEND PATCH v3 05/11] drm: add Atmel HLCDC Display Controller support

[Boris BREZILLON <boris.brezillon@free-electrons.com>]

On Sat, 12 Jul 2014 14:37:16 -0400
Rob Clark <robdclark@gmail.com> wrote:

> On Sat, Jul 12, 2014 at 2:16 PM, Boris BREZILLON
> <boris.brezillon@free-electrons.com> wrote:
> > Hello,
> >
> > On Mon,  7 Jul 2014 18:42:58 +0200
> > Boris BREZILLON <boris.brezillon@free-electrons.com> wrote:
> >
> >
> >> +int atmel_hlcdc_layer_disable(struct atmel_hlcdc_layer *layer)
> >> +{
> >> +     struct atmel_hlcdc_layer_dma_channel *dma = &layer->dma;
> >> +     unsigned long flags;
> >> +     int i;
> >> +
> >> +     spin_lock_irqsave(&dma->lock, flags);
> >> +     for (i = 0; i < layer->max_planes; i++) {
> >> +             if (!dma->cur[i])
> >> +                     break;
> >> +
> >> +             dma->cur[i]->ctrl = 0;
> >> +     }
> >> +     spin_unlock_irqrestore(&dma->lock, flags);
> >> +
> >> +     return 0;
> >> +}
> >
> >
> > I'm trying to simplify the hlcdc_layer code and in order to do that I
> > need to know what's expected when a user calls plane_disable (or more
> > exactly DRM_IOCTL_MODE_SETPLANE ioctl call with the frame buffer ID set
> > to 0).
> >
> > The HLCDC Display Controller support two types of disable:
> >
> > 1) The plane is disabled at the end of the current frame (the is the
> > solution I'm using)
> >
> > 2) The plane is disabled right away (I haven't tested it, but I think
> > this solution could generate some sort of artifacts for a short period
> > of time, because the framebuffer might be partially displayed)
> >
> > If solution 1 is chosen, should I wait for the plane to be actually
> > disabled before returning ?
> 
> for cursor in particular, if you block, it is going to be a massive
> slowdown for some apps.  I remember at least older gdm would rapidly
> flash a spinning cursor.  As a result, if you wait for vsync each
> time, it would take a couple minutes to login!

That makes sense.

> 
> if #2 works, I'd recommend it.  Otherwise you may have to do some of
> the same hijinks that I have to do in mdp4_crtc for the cursor.

I already have a working solution which does not block with #1, I was
just trying to simplify my code ;-).
I'll try #2 and if it works without any side effects I'll go for it.

Thanks,

Boris

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com