Re: [PATCH 1/2] drm/nouveau: Add DRM_IOCTL_NOUVEAU_GET_ZCULL_INFO

[Danilo Krummrich <dakr@kernel.org>]

On Fri, Mar 21, 2025 at 06:06:34PM -0400, M Henning wrote:
> On Thu, Mar 20, 2025 at 2:18 PM Danilo Krummrich <dakr@kernel.org> wrote:
> > On Wed, Mar 12, 2025 at 05:36:14PM -0400, Mel Henning wrote:
> > > +     __u32 width_align_pixels;
> > > +     __u32 height_align_pixels;
> > > +     __u32 pixel_squares_by_aliquots;
> > > +     __u32 aliquot_total;
> > > +     __u32 zcull_region_byte_multiplier;
> > > +     __u32 zcull_region_header_size;
> > > +     __u32 zcull_subregion_header_size;
> > > +     __u32 subregion_count;
> > > +     __u32 subregion_width_align_pixels;
> > > +     __u32 subregion_height_align_pixels;
> > > +
> > > +     __u32 ctxsw_size;
> > > +     __u32 ctxsw_align;
> > > +};
> >
> > What if this ever changes between hardware revisions or firmware versions?
> 
> There was some previous discussion of that here:
> https://gitlab.freedesktop.org/mesa/mesa/-/issues/12596#note_2796853
> 
> From what I can tell, this structure hasn't really changed since
> FERMI_C (circa 2011), so I'm not too worried about it changing on us
> too quickly. When it does change, we have the option of appending more
> members to this struct in the usual way, or if the change is more
> fundamental we can return an error from this ioctl and add a new
> interface. Userspace needs to handle an error from this ioctl
> gracefully anyway since whether it works or not depends on the gpu
> generation and what firmware is loaded right now.

We could also define it as

	struct drm_nouveau_get_zcull_info {
		__u32 version;
		__u32 _pad;

		union {
			struct drm_nouveau_get_zcull_info_v1 info;
		}
	}

just to be safe.