Re: [RFC PATCH 1/1] drm/meson: Support drm_panic

[Neil Armstrong]

Hi,

On 02/10/2024 13:02, Maxime Ripard wrote:
> + Jocelyn
>
> On Wed, Oct 02, 2024 at 09:59:57AM GMT, Neil Armstrong wrote:
> > > diff --git a/drivers/gpu/drm/meson/meson_plane.c b/drivers/gpu/drm/meson/meson_plane.c
> > > index b43ac61201f3..b2def784c00d 100644
> > > --- a/drivers/gpu/drm/meson/meson_plane.c
> > > +++ b/drivers/gpu/drm/meson/meson_plane.c
> > > @@ -20,6 +20,8 @@
> > >    #include <drm/drm_framebuffer.h>
> > >    #include <drm/drm_gem_atomic_helper.h>
> > >    #include <drm/drm_gem_dma_helper.h>
> > > +#include <drm/drm_gem_framebuffer_helper.h>
> > > +#include <drm/drm_panic.h>
> > >    #include "meson_plane.h"
> > >    #include "meson_registers.h"
> > > @@ -419,10 +421,49 @@ static void meson_plane_atomic_disable(struct drm_plane *plane,
> > >    	priv->viu.osd1_enabled = false;
> > >    }
> > > +static int meson_plane_get_scanout_buffer(struct drm_plane *plane,
> > > +					  struct drm_scanout_buffer *sb)
> > > +{
> > > +	struct meson_plane *meson_plane = to_meson_plane(plane);
> > > +	struct meson_drm *priv = meson_plane->priv;
> > > +	struct drm_framebuffer *fb;
> > > +
> > > +	if (!meson_plane->enabled)
> > > +		return -ENODEV;
> > > +
> > > +	if (priv->viu.osd1_afbcd) {
> > > +		if (meson_vpu_is_compatible(priv, VPU_COMPATIBLE_GXM)) {
> >
> > This should be meson_vpu_is_compatible(priv, VPU_COMPATIBLE_G12A)
> >
> > You should call:
> >
> > 			if (priv->afbcd.ops) {
> > 				priv->afbcd.ops->reset(priv);
> > 				priv->afbcd.ops->disable(priv);
> > 			}
>
> I'm not sure it's a good idea. This code is run in the panic path, and
> it comes with strict requirements that these functions don't have.
>
> It'll be incredibly easy to add a sleeping call or a lock in there.
>
> On a more fundamental level, I'm not sure we should be disableing AFBC
> at all. Do we even have the guarantee that the buffer is large enough to
> hold XRGB8888 pixels?

Yes it does, "compressed" is in he way pixels are ordered in memory, meaning
it will be faster to scanout when the image is simple, but with a fully random
image the buffer will be larger.

But per my comment, AFBC is really only used on Android producst since it requires
DRM_FORMAT_XBGR8888, so the best is to bail out when AFBC is enabled.

Neil

> Maxime